<PAGE>

                                                                     Exhibit 4.2

THIS DOCUMENT IS IMPORTANT AND REQUIRES YOUR IMMEDIATE ATTENTION. IF YOU ARE IN
ANY DOUBT AS TO THE ACTION YOU SHOULD TAKE, AND IF YOU ARE IN THE UK, YOU ARE
RECOMMENDED TO SEEK YOUR OWN PERSONAL FINANCIAL ADVICE IMMEDIATELY FROM YOUR
STOCKBROKER, BANK MANAGER, SOLICITOR, ACCOUNTANT OR OTHER INDEPENDENT FINANCIAL
ADVISER DULY AUTHORISED UNDER THE FINANCIAL SERVICES AND MARKETS ACT 2000. IF
YOU ARE OUTSIDE THE UK YOU SHOULD IMMEDIATELY CONSULT ANOTHER APPROPRIATELY
AUTHORISED INDEPENDENT FINANCIAL ADVISER.

The distribution of this document in jurisdictions other than the UK may be
restricted by law and therefore persons into whose possession this document
comes should inform themselves about and observe any of those restrictions. Any
failure to comply with any of those restrictions may constitute a violation of
the securities laws of any such jurisdiction.


The contents of this document and the Form of Acceptance, which have been
prepared by and are the sole responsibility of British Biotech plc, have been
approved by J.P. Morgan plc of 125 London Wall, London EC2Y 5AJ (regulated in
the UK by the Financial Services Authority) solely for the purposes of section
21 of the Financial Services and Markets Act 2000. J.P. Morgan plc is acting for
British Biotech plc and no one else in connection with the Offer and will not be
responsible to any other person for providing the protections afforded to
clients by J.P. Morgan plc or for providing advice in relation to the Offer.

                          -----------------------------

                                      OFFER

                                       BY

                               BRITISH BIOTECH PLC

                                       FOR

                            RIBOTARGETS HOLDINGS PLC


--------------------------------------------------------------------------------

TO ACCEPT THE OFFER, THE ACCOMPANYING FORM OF ACCEPTANCE SHOULD BE COMPLETED AND
RETURNED AS SOON AS POSSIBLE, AND IN ANY EVENT NOT LATER THAN 3.00P.M. ON 20TH
APRIL, 2003. THE PROCEDURE FOR ACCEPTANCE OF THE OFFER IS SET OUT ON PAGE 5 OF
THIS DOCUMENT AND IN THE ACCOMPANYING FORM OF ACCEPTANCE.





                                       1
<PAGE>



                                    CONTENTS



Letter from the Chairman of British Biotech plc

Appendix I - Conditions and further terms of the Offer

Appendix II - Definitions









                                       2
<PAGE>




                 LETTER FROM THE CHAIRMAN OF BRITISH BIOTECH PLC

                               BRITISH BIOTECH PLC

     (Incorporated in England and Wales under the Companies Acts 1985 with
                             Registered No.2304992)




                                                              Registered office:
                                                                    Thames Court
                                                                 Watlington Road
                                                                          Oxford
                                                             Oxfordshire OX4 6LY

                                                                21st March, 2003

To Ribotargets Shareholders and, for information only, to holders of Ribotargets
options

Dear Shareholder

            OFFER BY BRITISH BIOTECH PLC FOR RIBOTARGETS HOLDINGS PLC

1.       INTRODUCTION

1.1      British Biotech has today announced the terms of an offer to be made by
         British Biotech for the whole of the issued and to be issued share
         capital of Ribotargets.

1.2      This document contains the Offer. A Form of Acceptance for completion
         by you, if you wish to accept the Offer, is enclosed with this
         document. You are, however, also referred to the compulsory transfer
         provisions described in section 8 below.

2.       THE OFFER

2.1      British Biotech hereby offers to acquire all the Ribotargets Shares, on
         the terms and subject to the conditions set out in Appendix I of this
         document and in the Form of Acceptance.

2.2      The Ribotargets Shares will be acquired fully paid and free from all
         liens, charges and Encumbrances and together with all rights attaching
         to them as at the date of Completion including, without limitation, the
         right to receive all dividends and other distributions declared, made
         or paid by Ribotargets on or after Completion.

2.3      The Offer is conditional upon satisfaction or, where permitted, waiver
         of each of the Conditions set out in Part A of Appendix I and is
         subject to the further terms set out in Part B of Appendix I.

3.       UNDERTAKINGS

         British Biotech has received undertakings to accept the Offer in
         respect of:

         7,028,679 B ORDINARY SHARES, REPRESENTING 100 PER CENT. OF THE B
         ORDINARY SHARES IN ISSUE AS AT THE DATE OF THIS DOCUMENT;

         7,717,732 A ORDINARY SHARES, REPRESENTING 99.9 PER CENT. OF THE A
         ORDINARY SHARES IN ISSUE AS AT THE DATE OF THIS DOCUMENT; AND


                                       3
<PAGE>

         526,533 ORDINARY SHARES, REPRESENTING 100 PER CENT. OF THE ORDINARY
         SHARES IN ISSUE AS AT THE DATE OF THIS DOCUMENT.

         British Biotech has also received undertakings to accept the Offer in
         respect of any further B Ordinary Shares which are issued at or prior
         to Completion.

4.       CONSIDERATION

4.1      The consideration for the sale of the B Ordinary Shares will be
         satisfied by the issue and allotment by British Biotech at Completion
         to the B Ordinary Shareholders of:

         2.7883114505 BRITISH BIOTECH ORDINARY SHARES FOR EVERY B ORDINARY SHARE

4.2      The consideration for the sale of the A Ordinary Shares will be
         satisfied by the issue and allotment by British Biotech at Completion
         to the A Ordinary Shareholders of:

         0.8545918288 BRITISH BIOTECH ORDINARY SHARES FOR EVERY A ORDINARY SHARE

4.3      The consideration for the sale of the Ordinary Shares will be satisfied
         by the issue and allotment by British Biotech to the Ordinary
         Shareholders of a total of:

         396,198 BRITISH BIOTECH ORDINARY SHARES

         to be allocated amongst holders of Ordinary Shares pro rata to their
         holdings of Ordinary Shares immediately prior to Completion.

4.4      British Biotech Ordinary Shares issued in respect of fractional
         entitlements will not be allotted to Ribotargets Shareholders on
         Completion but will be aggregated and sold into the market and the
         gross proceeds will be retained for the benefit of British Biotech.

5.       CONSIDERATION SHARES

5.1      The Consideration Shares will be allotted, credited as fully paid, and
         will rank pari passu in all respects with the British Biotech Ordinary
         Shares in issue at the date of their allotment.

5.2      British Biotech will use all reasonable endeavours to ensure that all
         the Consideration Shares are admitted to the Official List by the UK
         Listing Authority and to trading on the market for listed securities of
         the London Stock Exchange on or as soon as reasonably practicable after
         their allotment. A copy of the Circular and Listing Particulars, which
         have today been issued to the shareholders of British Biotech,
         accompanies this document.

6.       PAYMENT OF CONSIDERATION

6.1      Any share certificates in respect of Consideration Shares to be issued
         by British Biotech to Ribotargets Shareholders who validly accept the
         Offer, and whose acceptances are complete in all respects, will be
         delivered as soon as practicable following Completion (and, in any
         event, within 10 days of Completion) to Ribotargets's Solicitors.
         Ribotargets's Solicitors will be responsible for distributing such
         documents to the Ribotargets Shareholders in accordance with the
         completed instructions in the Form of Acceptance.

6.2      All documents and remittances sent by or to the Ribotargets
         Shareholders will be sent at their risk and no acknowledgement of
         receipt will be given by British Biotech. If the Offer is withdrawn or
         terminates in accordance with its terms, the Form of Acceptance, share
         certificate(s) and/or other document(s) of title will be sent by post
         within 7 days of the Offer being withdrawn or terminating to the
         address set out in the Form of Acceptance or, if none is


                                       4
<PAGE>

         set out, to Ribotargets's Solicitors (who will be responsible for
         distributing such documents to the relevant Ribotargets Shareholders).

7.       PROCEDURE FOR ACCEPTANCE

7.1      To accept the Offer, you must complete and sign the accompanying Form
         of Acceptance in accordance with the instructions contained in it which
         form part of the terms of the Offer.

7.2      The Form of Acceptance, duly completed in all respects, should be
         returned, together with the relevant share certificate(s) and/or other
         document(s) of title, to the Company Secretary of British Biotech (at
         Thames Court, Watlington Road, Oxford, Oxfordshire OX4 6LY) so as to
         arrive as soon as possible, but in any event not later than 3.00 p.m.
         on 20th April, 2003.

7.3      Even if your share certificate(s) and/or other document(s) of title
         is/are not readily available or is/are lost, you should nevertheless
         complete, sign and return the Form of Acceptance as indicated above.
         The share certificate(s) and/or other document(s) of title should be
         forwarded as soon as possible thereafter, or, if you have lost your
         share certificate(s), a form of lost share certificate indemnity (a
         SHARE INDEMNITY) should be requested from the Company Secretary of
         British Biotech (Thames Court, Watlington Road, Oxford, Oxfordshire OX4
         6LY) and completed and signed as indicated. Although no Consideration
         Shares will be issued or allotted to you until such document(s), or a
         duly completed Share Indemnity in lieu thereof, is/are received,
         British Biotech reserves the right to treat acceptances of the Offer as
         valid, even though not complete in all respects or not accompanied by
         the relative share certificate(s) and/or other document(s) of title.

8.       COMPULSORY TRANSFER PROVISIONS

8.1      The Ribotargets Articles provide that if the holder(s) of at least 65%
         by nominal value of the B Ordinary Shares and the A Ordinary Shares (an
         INVESTOR MAJORITY) intend to sell all of their holdings of shares in
         Ribotargets to a purchaser who has made a bona fide offer on arm's
         length terms for the entire issued share capital of Ribotargets, such
         Investor Majority may issue a Selling Notice to Ribotargets stating the
         place, date and time of completion of the proposed sale and setting out
         the terms and conditions of such offer to be extended to the other
         Ribotargets Shareholders. The date of completion must be at least 14
         days from the date of the Selling Notice.

8.2      As noted in section 3 of this letter, more than 65% by nominal value of
         the B Ordinary Shareholders and the A Ordinary Shareholders have
         entered into undertakings to accept the Offer. In accordance with the
         Articles, such shareholders (the SELLERS) have today issued a Selling
         Notice to Ribotargets. The date of completion (which will be at least
         14 days from the date of the Selling Notice) is the date upon which the
         Offer becomes unconditional, save only as to the Escrow Condition.

8.3      Upon receipt of the Selling Notice referred to above, the Ribotargets
         Articles oblige Ribotargets to send a Compulsory Sale Notice to each of
         the Ribotargets Shareholders (other than the Sellers), giving the
         details of the terms of offer as set out in the Selling Notice and
         requiring each of them to sell all of their Ribotargets shares to
         British Biotech on such terms. A Compulsory Sale Notice has been, or if
         the Offeror requires, will be sent to those Ribotargets Shareholders
         who are not Sellers with this Offer.

8.4      The Articles provide that if a Ribotargets Shareholder fails to comply
         with the Compulsory Sale Notice given to him (a DEFAULTING MEMBER),
         Ribotargets is constituted as the agent of any such Defaulting Member
         for the sale of its shares in Ribotargets in accordance with the
         Compulsory Sale Notice and the directors of Ribotargets are entitled to
         authorise any person


                                       5
<PAGE>

         to execute and deliver the necessary transfer(s) on behalf of a
         Defaulting Member and cause the purchaser (in this case British
         Biotech) to be registered as the holder of such shares.

8.5      Accordingly, if you do not accept the Offer by completing and returning
         the Form of Acceptance in accordance with the procedure set out in
         section 7 of this letter, the Articles authorise the directors of
         Ribotargets to transfer your shares in Ribotargets to British Biotech
         in consideration for the issue and allotment of the appropriate number
         of Consideration Shares, calculated in accordance with section 4 of
         this letter. However, if you do not accept the Offer by completing and
         returning the Form of Acceptance in accordance with section 7 of this
         letter, the Consideration Shares to be issued and allotted to you in
         respect of the transfer of your shares in Ribotargets will be issued to
         Ribotargets who will hold such Consideration Shares on trust for you in
         accordance with the Ribotargets Articles. The Consideration Shares to
         which you are entitled under the Offer will only be transferred from
         Ribotargets to you (or to your nominee) once you have delivered the
         relevant share certificates in respect of your shares in Ribotargets
         (or a Share Indemnity) to the Company Secretary of British Biotech.

9.       FURTHER INFORMATION

9.1      Your attention is drawn to the Form of Acceptance and to the following
         Appendices which form part of this document:

<TABLE>
<CAPTION>

<S>                                    <C>
         Appendix I                    Conditions and further terms of the Offer
         Appendix II                   Definitions

</TABLE>

10.      ACTION TO BE TAKEN

10.1     To accept the Offer, the Form of Acceptance must be completed and
         returned. Forms of Acceptance should be completed and returned as soon
         as possible and, in any event so as to be received by the Company
         Secretary of British Biotech at Thames Court, Watlington Road, Oxford,
         Oxfordshire OX4 6LY not later than 3.00 p.m. on 20th April, 2003.



Yours faithfully
Peter Fellner

Chairman
British Biotech plc




                                       6
<PAGE>




                                   APPENDIX I

                CONDITIONS AND CERTAIN FURTHER TERMS OF THE OFFER

PART A: CONDITIONS OF THE OFFER

1.       The Offer is subject to the following conditions being fulfilled or,
         where appropriate, waived:

         (a) valid acceptances being received (and not, where permitted,
             withdrawn) in respect of not less than 100 per cent. in nominal
             value (or such lesser percentage as the Offeror may decide) of the
             Ribotargets Shares in issue at the date of this document and issued
             in accordance with the Contribution Deed;

         (b) resolutions to approve the Capital Reorganisation (as defined in
             the Circular and Listing Particulars) and the purchase of the
             Ribotargets Shares (as set out in Resolutions 1 and 2 of the notice
             of Extraordinary General Meeting contained in the Circular and
             Listing Particulars) being passed at an extraordinary general
             meeting of British Biotech and becoming unconditional;

         (c) a resolution approving the waiver of any obligation on the
             Ribotargets Shareholders and directors of British Biotech to make a
             general offer for British Biotech under Rule 9 of the Code (as set
             out in Resolution 3 of the notice of Extraordinary General Meeting
             contained in the Circular and Listing Particulars) being passed at
             an extraordinary general meeting of the independent shareholders
             (for the purposes of the Code) of British Biotech;

         (d) the admission to the Official List and to trading on the London
             Stock Exchange of the Consideration Shares becoming effective (in
             accordance with the Listing Rules of the UK Listing Authority and
             the rules of the London Stock Exchange);

         (e) no material breach of the Warranties coming to the notice of
             British Biotech;

         (f) no Executive being in breach of any obligation on his part, under
             clause 2.4 of the Undertaking, to deliver to British Biotech, not
             later than 5 Business Days after 31st March, 2003, the Ribotargets
             Balance Sheet satisfactory to British Biotech, together with such
             supporting information as British Biotech may reasonably require,
             demonstrating that the Ribotargets Net Working Capital was not less
             than Pound Sterling 8,200,000;

         (g) no Ribotargets Shareholder or director of Ribotargets who has
             entered into the Undertaking being in material breach of any
             obligation (other than the Completion Delivery Obligations) on its
             part under the Undertaking and, where that breach is capable of
             remedy, it is not remedied to British Biotech's reasonable
             satisfaction;

         (h) the issue of the Compulsory Sale Notice by Ribotargets to each
             Ribotargets Shareholder who is a Ribotargets Shareholder at the
             date of this document and has not entered into the Undertaking as
             soon as reasonably practicable and in any event not later than 2
             Business Days after the date of this document or such other date as
             British Biotech may specify;

         (i) the issue of the Compulsory Sale Notice by Ribotargets to each
             person who becomes a Ribotargets Shareholder between the date of
             this document and Completion as soon as reasonably practicable and
             in any event not later than 2 Business Days following


                                       7
<PAGE>

             the date that such person becomes a Ribotargets Shareholder or
             such other date as British Biotech may specify; and

         (j) the subscription by the Relevant Investors for additional B
             Ordinary Shares in accordance with the terms of the Contribution
             Deed.

2.       British Biotech may waive all or any of Conditions (a) to (c) and (e)
         to (j) above (either in whole or in part) at any time by notice in
         writing to Ribotargets's Solicitors.

PART B: FURTHER TERMS OF THE OFFER

The following further terms apply to the Offer:

1.       If:

         (a) any material breach of the Warranties comes to the notice of
             British Biotech; or

         (b) any Executive breaches any obligation on his part, under clause 2.4
             of the Undertaking, to deliver to British Biotech, not later than 5
             Business Days after 31st March, 2003, the Ribotargets Balance Sheet
             satisfactory to British Biotech, together with such supporting
             information as British Biotech may reasonably require,
             demonstrating that the Ribotargets Net Working Capital was not less
             than Pound Sterling 8,200,000; or

         (c) any Ribotargets Shareholder or director of Ribotargets who has
             entered into the Undertaking is in material breach of any
             obligation (other than the Completion Delivery Obligations) on its
             part under the Undertaking and, where that breach is capable of
             remedy, it is not remedied to British Biotech's reasonable
             satisfaction,

         then, but without prejudice to any other rights or remedies available
         to British Biotech, British Biotech may without any liability to the
         Ribotargets Shareholders elect to withdraw the Offer by giving notice
         in writing to Ribotargets's Solicitors.

2.       Subject to paragraph 1, the Offer is open for acceptance by every
         recipient until the date upon which the Offer becomes wholly
         unconditional, save as to the Escrow Condition. If the Offer becomes
         unconditional, it will remain open for acceptance for not less than 14
         days from the date on which the Offer became wholly unconditional.

3.       Acceptances of the Offer will be deemed to be withdrawn if the Offeror

         (a) does not deliver to Ribotargets's Solicitors, not later than 5
             Business Days after 31st March, 2003, the British Biotech Balance
             Sheet satisfactory to an Investor Majority, together with such
             supporting information as an Investor Majority may reasonably
             require, demonstrating that the British Biotech Net Working Capital
             was not less than Pound Sterling 23,500,000;

         (b) is in material breach of any obligation on its part under the
             Covenant Deed and, where that breach is capable of remedy, it is
             not remedied to the reasonable satisfaction of an Investor
             Majority.

         Acceptances are otherwise irrevocable.

4.       The Offer will lapse and entirely terminate if all the Conditions have
         not been fulfilled or waived by midnight on 30th April, 2003 or such
         later date as British Biotech and Ribotargets may agree.


                                       8
<PAGE>


5.       The Ribotargets Shares will be acquired free from all liens, charges,
         and Encumbrances and together with all rights attached to them as at
         the date of Completion.

6.       Any Consideration Shares allotted to a Ribotargets Shareholder located
         in the United States or that is a US Person will be issued in
         certificated form and each share certificate issued to a US Person
         shall bear a legend to the following effect:

         "THE SHARES REPRESENTED BY THIS CERTIFICATE WERE ORIGINALLY ISSUED IN A
         TRANSACTION EXEMPT FROM REGISTRATION UNDER THE UNITED STATES SECURITIES
         ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND MAY NOT BE OFFERED,
         SOLD, PLEDGED, TRANSFERRED OR OTHERWISE DISPOSED OF IN THE ABSENCE OF
         SUCH REGISTRATION OR ANY APPLICABLE EXEMPTION THEREFROM. EACH HOLDER OF
         THIS CERTIFICATE AGREES FOR THE BENEFIT OF THE ISSUER THAT IT WILL NOT
         (ON ITS OWN BEHALF OR ON BEHALF OF ANYONE ELSE) OFFER, SELL, TRANSFER,
         PLEDGE OR OTHERWISE DISPOSE OF THE SHARES REPRESENTED HEREBY, EXCEPT:
         (1) TO THE ISSUER; (2) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT
         FILED WITH THE SEC; (3) IN AN OFFSHORE TRANSACTION MEETING THE
         REQUIREMENTS OF RULE 903 OR 904 OF REGULATION S UNDER THE SECURITIES
         ACT; (4) IN A TRANSACTION EXEMPT FROM REGISTRATION UNDER THE SECURITIES
         ACT UNDER RULE 144 (IF AVAILABLE); OR (5) IN ANOTHER TRANSACTION EXEMPT
         FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT TO A
         TRANSFEREE WHO HAS FURNISHED SUCH CERTIFICATES AND OPINIONS OF COUNSEL
         AS THE ISSUER MAY REQUEST, AND IN THE CASE OF CLAUSES (4) THROUGH (5)
         ABOVE IN ACCORDANCE WITH ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF
         THE UNITED STATES. NOTWITHSTANDING ANYTHING TO THE CONTRARY IN THE
         FOREGOING, THE SHARES REPRESENTED HEREBY MAY NOT BE DEPOSITED INTO ANY
         UNRESTRICTED DEPOSITARY RECEIPT FACILITY IN RESPECT OF SHARES OF THE
         ISSUER ESTABLISHED OR MAINTAINED BY A DEPOSITARY BANK. THE HOLDER WILL,
         AND EACH SUBSEQUENT US PERSON IS REQUIRED TO, NOTIFY ANY SUBSEQUENT
         PURCHASER OF SHARES FROM IT OF THE FOREGOING RESTRICTIONS."

7.       This document has been prepared for the purpose of compliance with
         English law. It may not contain all the information required to be
         contained in disclosure documents under Australian law. British Biotech
         is not subject to the continuous disclosure requirements of the
         Corporations Act 2001 (Cth) (the CORPORATIONS ACT) that apply in
         Australia.

8.       The Offer is being made on the basis of Australian Securities &
         Investments Commission Class Order 00/214. Accordingly, the Offer is
         made without a disclosure document for the purposes of the Corporations
         Act.

9.       A Ribotargets Shareholder may not sell any Consideration Shares it
         receives under the Offer in Australia within 12 months after the issue
         of such Consideration Shares, except in circumstances where disclosure
         to investors under Part 6D.2 of the Corporations Act would not be
         required.

10.      Disclosure to investors would not generally be required under Chapter
         6D of the Corporations Act where any Consideration Shares are offered
         for sale:

         (a) on the London Stock Exchange;

         (b) to categories of "professional investors" described in section
             708(11) of the Corporations Act; or


                                       9
<PAGE>

         (c) to persons who are "sophisticated investors" and meet the criteria
             set out in section 708(8) or 708(10) of the Corporations Act.

         However, Chapter 6D of the Corporations Act is complex and you should
         consult your professional advisors if in any doubt regarding your
         position.

11.      The Consideration Shares will not be offered, directly or indirectly,
         in Belgium in a public transaction (as defined in article 2 of the
         Belgian Royal Decree of 7th July, 1999 on the public nature of the
         financial transactions). The issue of the Consideration Shares has not
         been notified to, and this document and the Form of Acceptance have not
         been approved by, the Belgian Banking and Finance Commission
         ("Commission bancaire et financiere" / "Commissie voor het Bank- en
         Financiewezen"). The Consideration Shares may only be sold in Belgium
         to investors in accordance with the provisions of article 3 of the
         Belgian Royal Decree of 7th July, 1999 on the public nature of the
         financial transactions (PROFESSIONAL INVESTORS), and this document and
         the Form of Acceptance may not be delivered or passed on to any
         investors other than professional investors.

12.      The instructions and authorities contained in, and the terms of, the
         Form of Acceptance constitute part of the terms of the Offer.

13.      The Offer and all acceptances thereof and the Form of Acceptance shall
         be governed by and construed in accordance with English law.

14.      The accidental omission to despatch this document to, or any failure to
         receive the same by, any person to whom the Offer is made, or should be
         made, shall not invalidate the Offer in any way. All communications,
         notices, certificates, documents of title and remittances to be
         delivered by or sent to or from Ribotargets Shareholders will be
         delivered by or sent to or from them (or their designated agents) at
         their own risk. No acknowledgement of receipt of any Form of
         Acceptance, share certificate(s) or other documents of title will be
         given. British Biotech reserves the right to treat acceptances of the
         Offer as valid although not accompanied by the relative share
         certificate(s) and/or other documents of title or otherwise not in
         order.

15.      All powers of attorney and authorities on the terms conferred by or
         referred to in this Appendix I or in the Form of Acceptance are given
         by way of security for the performance of the obligations of the
         Ribotargets Shareholder concerned and are irrevocable in accordance
         with section 4 of the Powers of Attorney Act 1971.

16.      Each Ribotargets Shareholder by whom, or on whose behalf, the Form of
         Acceptance is executed irrevocably undertakes, warrants and agrees to
         and with British Biotech (so as to bind him, his personal
         representatives, heirs, successors and assigns) to the following
         effect:

         (a) that the execution of the Form of Acceptance by it constitutes (i)
             an acceptance of the Offer in respect of the number of Ribotargets
             Shares inserted or deemed to be inserted in the Form of Acceptance,
             subject to the terms and conditions set out or referred to in this
             document and the Form of Acceptance and (ii) a waiver of any rights
             of pre-emption under the Ribotargets Articles or otherwise in
             respect of the transfer of any of the Ribotargets Shares;

         (b) that the Ribotargets Shares in respect of which the Offer is
             accepted or deemed to be accepted by it are sold free from all
             liens, charges or Encumbrances and together with all rights
             attaching thereto as at the date of Completion;

         (c) that British Biotech shall be entitled, once the Offer becomes
             unconditional, to direct the exercise of any votes attaching to any
             Ribotargets Shares in respect of which the


                                       10
<PAGE>

             Offer has been accepted or is deemed to have been accepted by it,
             and that the execution of the Form of Acceptance by it constitutes
             an authority to Ribotargets from such Ribotargets Shareholder to
             send any notice which may be required to be sent to him as a member
             of Ribotargets to British Biotech at its registered office, and an
             authority to any director of British Biotech to act as his attorney
             with the power to sign any consent to short notice of a general
             meeting on his behalf and/or to execute a form of proxy in respect
             of such Ribotargets Shares appointing any person determined by
             British Biotech to attend general meetings of Ribotargets and to
             exercise the votes attaching to such Ribotargets Shares on its
             behalf, where relevant, such votes to be cast as British Biotech
             may determine and prior to the Offer becoming unconditional, such
             Ribotargets Shareholder shall exercise his votes in relation to
             such resolutions as may be reasonably necessary to enable the Offer
             to be implemented provided that, in the case of a Ribotargets
             Shareholder executing a Form of Acceptance in the capacity of
             trustee, the appointment of the attorney is made in accordance with
             section 25 of the Trustee Act 1925 and shall be effective for the
             period of 12 months from the date of the Form of Acceptance;

         (d) that the execution of the Form of Acceptance constitutes, subject
             to the Offer becoming unconditional, in accordance with its terms:

             (i)    the irrevocable appointment by it of any director of British
                    Biotech as such Ribotargets Shareholder's attorney, and an
                    irrevocable instruction to the attorney, on behalf of such
                    Ribotargets Shareholder and in his name:


                    (A) to execute and complete all or any form(s) of transfer
                        and/or other document(s) at the attorney's discretion in
                        relation to the Ribotargets Shares referred to in
                        paragraph 1 of the Form of Acceptance in favour of
                        British Biotech or of such other person as
                        British Biotech may direct;


                    (B) to deliver such form(s) of transfer and/or other
                        document(s) at the attorney's discretion together with
                        the certificate(s) and/or other document(s) relating to
                        such Ribotargets Shares for registration; and



                    (C) to do all such other acts and things as may, in the
                        opinion of such attorney, be necessary or expedient for
                        the purpose of, or in connection with, the acceptance of
                        the Offer and to vest in British Biotech or such persons
                        as it may direct such Ribotargets Shares,

                    provided that, in the case of a Ribotargets Shareholder
                    executing a Form of Acceptance in the capacity of trustee,
                    the appointment of the attorney is made in accordance with
                    section 25 of the Trustee Act 1925 and shall be effective
                    for the period of 12 months from the date of the Form of
                    Acceptance


             (ii)   an irrevocable authority and request from it to Ribotargets
                    to register the transfer of its Ribotargets Shares pursuant
                    to the Offer and to deliver any share certificate(s) in
                    respect thereof (or a Share Indemnity in lieu thereof) to
                    British Biotech or as it may direct at the risk of such
                    Ribotargets Shareholder;


         (e) that he will deliver to British Biotech at its registered office
             his share certificate(s) and/or other document(s) of title in
             respect of his Ribotargets Shares, or a Share Indemnity in lieu
             thereof, as soon as possible and in any event prior to the Offer
             becoming unconditional;



                                       11
<PAGE>

         (f) that the terms of this paragraph shall be deemed to be incorporated
             in and form part of the Form of Acceptance, which shall be read and
             construed accordingly;

         (g) that, if he accepts the Offer, he shall do all such acts and things
             as shall be necessary or expedient to vest in British Biotech or
             its nominees the Ribotargets Shares held by him at Completion and
             in respect of which the Offer is accepted, including discharging
             any liens, charges or Encumbrances over such Ribotargets Shares;

         (h) that he agrees to ratify each and every lawful act or thing which
             may be done or effected by any director of British Biotech in the
             exercise of any of his powers and/or authorities hereunder; and

         (i) that, in the event of the Offer being withdrawn or terminating,
             such Form of Acceptance shall constitute his irrevocable authority
             and request to British Biotech to return his Form of Acceptance and
             the relevant share certificate(s) and or the document(s) of title
             in respect of the Ribotargets Shares held by him (or the Share
             Indemnity in lieu thereof) for which he has accepted the Offer by
             ordinary post at his risk to Ribotargets's Solicitors.

         References in this paragraph to Ribotargets Shareholders shall include
         references to the person or persons executing a Form of Acceptance and,
         in the event of more than one person executing a Form of Acceptance,
         the provisions of this paragraph shall apply to them jointly and to
         each of them.

Dated: 21st March, 2003



                                       12
<PAGE>



                                   APPENDIX II

                                   DEFINITIONS

In this document the following definitions apply unless the context requires
otherwise:

A ORDINARY SHARES means the A ordinary shares of Pound Sterling 0.10 each in the
capital of Ribotargets and A ORDINARY SHAREHOLDER means a holder of any of them;

B ORDINARY SHARES means the B ordinary shares of Pound Sterling 0.10 each in the
capital of Ribotargets and B ORDINARY SHAREHOLDER means a holder of any of them;

BRITISH BIOTECH means British Biotech plc (registered number 2304992) whose
registered address is Thames Court, Watlington Road, Oxford, Oxfordshire OX4
6LY;

BRITISH BIOTECH BALANCE SHEET means the consolidated balance sheet of British
Biotech and its subsidiaries as at 31st March, 2003 prepared in the form and
including the items shown in the schedule to the Undertaking headed "British
Biotech Balance Sheet", including, without limitation, full accruals for all
costs incurred in connection with the Offer, and prepared in accordance with the
accounting policies, principles, practices, evaluation rules and procedures,
methods and bases adopted by British Biotech in the preparation of the British
Biotech Management Accounts;

BRITISH BIOTECH MANAGEMENT ACCOUNTS means the unaudited management accounts of
British Biotech for the period of ten months ended 28th February, 2003 in the
Agreed Form;

BRITISH BIOTECH NET WORKING CAPITAL means the net working capital of British
Biotech as at 31st March, 2003 as indicated on line 14 of the British Biotech
Balance Sheet;

BRITISH BIOTECH ORDINARY SHARES means ordinary shares of 5 pence each in the
capital of British Biotech;

BUSINESS DAY means a day (other than a Saturday or Sunday) on which banks are
generally open in London for normal business;

CIRCULAR AND LISTING PARTICULARS means the document dated on or about the date
of this document comprising the combined circular to shareholders and listing
particulars of British Biotech in connection with the Offer;

CODE means The City Code on Takeovers and Mergers;

COMPLETION means completion of the acquisition of the Ribotargets Shares by
British Biotech, in respect of which the Offer has been accepted, and the
admission to listing and trading of the Consideration Shares;

COMPLETION DELIVERY OBLIGATIONS means the obligations specified in clauses
4.4(d)(i) and (iii), 4.4(e)(i), (ii) and (iv) and 4.4(f) of the Undertaking;

COMPULSORY SALE NOTICE means the notice issued or to be issued by Ribotargets
(in accordance with article 7.5.2 of the Ribotargets Articles) to any
Ribotargets Shareholders who have not entered into the Undertaking, giving the
details contained in the Selling Notice and requiring the Ribotargets
Shareholders to sell their holdings of shares in Ribotargets to British Biotech
on the terms contained in the Selling Notice;

CONDITIONS means the conditions set out in paragraph 1 of Part A of Appendix I
to this document;

                                       13
<PAGE>

CONSIDERATION SHARES means the 33,375,889 British Biotech Ordinary Shares to be
allotted and issued credited as fully paid to the Ribotargets Shareholders in
accordance with the terms of the Offer;

CONTRIBUTION DEED means the deed entered into among the Ribotargets Shareholders
and Ribotargets on or before the date of this document pursuant to which, inter
alia, the Relevant Investors will subscribe for further B Ordinary Shares at or
prior to Completion;

COVENANT DEED means the deed poll entered into by British Biotech prior to the
date of this document giving covenants with respect to the conduct of British
Biotech's business pending Completion;

DEFAULTING MEMBER means any member of Ribotargets who fails to comply with the
terms of the Compulsory Sale Notice;

ENCUMBRANCE means any mortgage, charge (fixed or floating), pledge, lien,
option, right to acquire, assignment by way of security, trust arrangement for
the purpose of providing security or any other security interest of any kind,
including retention arrangements and any agreement to create any of the
foregoing;

ESCROW CONDITION means the Condition set out in paragraph 1(d) of Part A of
Appendix I to this document having been satisfied and the Offer not having been
withdrawn before satisfaction of such Condition;

EXECUTIVE has the meaning given to it in the Undertaking;

FORM OF ACCEPTANCE means the form of acceptance and authority accompanying this
document;

INVESTOR MAJORITY means the holders of at least 65 per cent. by nominal value of
the B Ordinary Shares and the A Ordinary Shares;

LONDON STOCK EXCHANGE means London Stock Exchange plc;

NEW RIBOTARGETS SHARES means the B Ordinary Shares which are subscribed for by
the Relevant Investors at or prior to Completion in accordance with the terms of
the Contribution Deed;

OFFER means the offer by British Biotech to acquire all the Ribotargets Shares
on the terms and subject to the conditions set out in this document and in the
Form of Acceptance;

OFFICIAL LIST means the official list of the UK Listing Authority;

ORDINARY SHARES means the ordinary shares of Pound Sterling 0.10 each in the
capital of Ribotargets and ORDINARY SHAREHOLDER means a holder of any of them;

RELEVANT INVESTORS means the Ribotargets Shareholders named in column (1) of
schedule 4 to the Contribution Deed;

RIBOTARGETS means Ribotargets Holdings plc (registered number 3339154) whose
registered office is at Granta Park, Abington, Cambridge CB1 6GB;

RIBOTARGETS ARTICLES means the articles of association of Ribotargets in force
as at the date of this document;

RIBOTARGETS BALANCE SHEET means the consolidated balance sheet of the
Ribotargets and its subsidiary as at 31st March, 2003 prepared in the form and
including the items shown in the schedule to the Undertaking headed "Ribotargets
Balance Sheet", including, without limitation, full accruals for all costs
incurred in connection with the Offer, and prepared in accordance with the
accounting


                                       14
<PAGE>

policies, principles, practices, evaluation rules and procedures, methods and
bases adopted by Ribotargets in the preparation of the Ribotargets Management
Accounts;

RIBOTARGETS MANAGEMENT ACCOUNTS means the unaudited management accounts of
Ribotargets for the period ended 2nd March, 2003 in the Agreed Form;

RIBOTARGETS NET WORKING CAPITAL means the net working capital of Ribotargets as
at 31st March, 2003 as indicated on line 13 of the Ribotargets Balance Sheet;

RIBOTARGETS SHARES means all the existing issued Ordinary Shares, A Ordinary
Shares or B Ordinary Shares and any further such shares which are allotted or
issued before the date upon which the Offer becomes wholly unconditional (save
only as to the Escrow Condition), including any New Ribotargets Shares which are
issued pursuant to the Contribution Deed, and RIBOTARGETS SHAREHOLDER means a
holder of any of them;

RIBOTARGETS'S SOLICITORS means CMS Cameron McKenna of Mitre House, 160
Aldersgate Street, London EC1A 4DD (ref: MGD);

SECURITIES ACT means the United States Securities Act of 1933, as amended;

SELLING NOTICE means the notice issued or to be issued to Ribotargets by those
Ribotargets Shareholders named in schedule 1 to the Undertaking in accordance
with article 7.5.1 of the Articles;

SUBSIDIARY means a subsidiary for the purposes of the Companies Act 1985;

UK LISTING AUTHORITY means the Financial Services Authority acting in its
capacity as the competent authority for the purposes of Part VI of the Financial
Services and Markets Act 2000;

UNDERTAKING means the undertakings between those Ribotargets Shareholders named
in schedule 1 to that agreement, the Executives and British Biotech dated on or
prior to the date of this document;

UNITED STATES and US PERSON have the meanings given in Rule 902 of Regulation S
under the Securities Act; and

WARRANTIES has the meaning given to it in the Undertaking.


                                       15











<PAGE>








                                DEED OF COVENANT


                              DATED 17th MARCH , 2003


                               BRITISH BIOTECH PLC







                                 ALLEN & OVERY
                                     London


<PAGE>








THIS DEED is executed as a deed poll on 17th March, 2003 by BRITISH BIOTECH PLC
(registered number 2304992) whose registered office is at Thames Court,
Watlington Road, Oxford, Oxfordshire OX4 6LY (the COMPANY).

WHEREAS the Company has agreed with Ribotargets Holdings plc to conduct its
business in accordance with the terms and subject to the conditions set out in
this deed poll.

NOW THIS DEED POLL WITNESSES AND IT IS DECLARED as follows:

1.       INTERPRETATION

1.1      In this deed poll:

         BRITISH BIOTECH GROUP COMPANIES means the Company each of its
         subsidiaries and subsidiary undertakings and BRITISH BIOTECH GROUP
         COMPANY means any of them;

         BUDGET means the 2003 budget for the Company set out in schedule 1;

         CIRCULAR AND LISTING PARTICULARS means the document comprising the
         combined circular to shareholders and listing particulars of the
         Company which is required in connection with the Offer;

         COMPLETION means completion of the acquisition by the Company of the
         entire issued and to be issued share capital of Ribotargets;

         EMPLOYEE includes a director and any officer of the Company whether or
         not he has entered into or works under (or, where the employment has
         ceased, worked under) a contract of employment;

         EXTERNAL COST means any category of expenditure other than an Internal
         Cost;

         INTELLECTUAL PROPERTY RIGHTS means rights in trade marks, rights in
         designs, patents, copyright, moral rights, database rights, rights in
         know-how and all other intellectual property rights in each case
         whether registered or unregistered, together with applications for the
         grant of any of these rights, and together also with all rights or
         forms of protection having equivalent or similar effect to any of the
         foregoing which may subsist anywhere in the world;

         INTERNAL COST means any category of expenditure which falls (on the
         basis of preparation consistent with the Company's prior financial
         year) to be treated as an internal cost for the purposes of preparing
         the Budget;

         OFFER means an offer to acquire the entire issued and to be issued
         share capital of Ribotargets on the terms and subject to the conditions
         to be set out in an offer document to be issued in final form by the
         Company;

         RETIREMENT/DEATH/DISABILITY BENEFIT means any pension, lump sum,
         gratuity or other like benefit given or to be given on retirement or on
         death, or in anticipation of retirement, or, in connection with past
         service, after retirement or death, or to be given on or in
         anticipation of or in connection with any change in the nature of the
         service of the employee in question or given or to be given on or in
         connection with the illness, injury or disability of, or suffering of
         any accident by, an employee;



                                       1
<PAGE>

         RIBOTARGETS means Ribotargets Holdings plc (registered number 3339154)
         whose registered office is at Granta Park, Abington, Cambridge CB1 6GB;

         SCHEMES means the Standard Life Occupational Contracted-in Money
         Purchase Scheme and the Scottish Mutual Group Person Pension Scheme of
         the Company;

         SUBSIDIARY means a subsidiary for the purposes of the Companies Act
         1985; and

         SUBSIDIARY UNDERTAKING has the meaning given in section 258 of the
         Companies Act 1985.

1.2      References to THIS DEED POLL are to this deed poll and the schedule.

1.3      The headings in this deed poll do not affect its interpretation.

2.       CONDUCT OF BUSINESS

2.1      Subject to subclause 2.2 and clause 4, the Company covenants to
         Ribotargets that, pending Completion and except with the prior written
         consent of either:

         (a) Simon Sturge of Granta Park, Abington, Cambridge CB1 6GB; or

         (b) the holders of more than 65 per cent. by nominal value of the
             issued B Ordinary Shares and A Ordinary Shares of Ribotargets,

         such consent not to be unreasonably withheld or delayed, the Company
         shall not (and shall procure that each British Biotech Group Company
         shall not), save for the purposes of Completion or as envisaged in the
         Circular and Listing Particulars:

         (a) incur any expenditure in respect of:

             (i)    any Internal Cost in excess of Pound Sterling 20,000 per
                    item or Pound Sterling 100,000 in aggregate (other than
                    expenditure expressly specified in the Budget in respect of
                    any Internal Cost); and

             (ii)   any External Cost in excess of Pound Sterling 50,000 per
                    item; or

         (b) dispose of or grant any option or right of pre-emption in respect
             of any part of its assets; or

         (c) dispose of or grant any licence in respect of any interest in its
             Intellectual Property Rights other than pursuant to an agreement
             relating to the transfer of materials or a confidentiality
             agreement entered into in the ordinary course of its business; or

         (d) borrow any money; or

         (e) enter into any unusual or abnormal contract or commitment or:

             (i)    grant any lease or third party right in respect of any real
                    estate or transfer or otherwise dispose of any real estate;

             (ii)   make any loan;

             (iii)  enter into any leasing, hire purchase or other agreement or
                    arrangements for payment on deferred terms; or


                                       2
<PAGE>

         (f) declare, make or pay any dividend or other distribution; or

         (g) grant, issue or redeem any mortgage, charge, debenture or other
             security or give any guarantee or indemnity; or

         (h) make any change in the terms and conditions of employment of any of
             its directors or employees or employ or terminate the employment of
             any person save for cause; or

         (i) make, or announce to any person any proposal to make, any change
             or addition to any retirement/death/disability benefit in respect
             of any of its directors or employees or former directors or former
             employees (or any dependant of any such person) or to the Schemes
             or grant or create any additional retirement/death/disability
             benefit or, without limiting the foregoing, take any action or
             allow any action to be taken in relation to the Schemes other than
             in the ordinary course of administering the Schemes or omit to
             take any action reasonably required for the ordinary operation of
             the Schemes; or

         (j) permit any of its insurances to lapse; or

         (k) create, issue, purchase or redeem any class of share or loan
             capital, or grant any option or right to subscribe any share or
             loan capital; or

         (l) pass any resolution of its shareholders or any class of
             shareholders, whether in general meeting or otherwise; or

         (m) agree, conditionally or unconditionally, to do any of the
             foregoing; or

         (n) in any other way depart from the ordinary course of its day-to-day
             trading.

2.2      Clause 2.1 shall not operate so as to restrict or prevent:

         (a) any matter reasonably undertaken in response to events beyond the
             control of the Company with the intention of minimising any adverse
             effect of such events provided that a director of the Company will
             inform Ribotargets of such matters as soon as reasonably
             practicable;

         (b) completion or performance of any obligations undertaken pursuant to
             any contract or arrangement entered into and disclosed to
             Ribotargets prior to the date of this deed poll;

         (c) any other matter undertaken at the written request of Ribotargets;
             or

         (d) any action or omission which the Company is required to take or
             omit to take by any applicable law or regulation.

2.3      British Biotech shall immediately notify Ribotargets (for the attention
         of Simon Sturge) in writing of any matter or thing which arises or
         becomes known to it before Completion which constitutes (or would after
         the lapse of time constitute) a breach of its undertakings under this
         deed poll.

3.       EGM

         If the Company makes the Offer to the shareholders of Ribotargets, the
         Company covenants to Ribotargets that it will use reasonable endeavours
         to convene an extraordinary general



                                       3
<PAGE>

         meeting of its shareholders, for the purpose of, inter alia, approving
         the purchase of the shares in Ribotargets, as soon as reasonably
         practicable after the date the Offer is made.

4.       TERMINATION

         If the Company does not make the Offer on or before the date which is
         10 days from the date of this deed poll all the provisions of this deed
         poll and all rights and obligations under it (except for this clause
         and clause 5) shall lapse and cease to have effect, including, but
         without limitation, any right to bring or cause to be brought any
         claim, action or proceeding under this deed poll and the Company shall
         have no liability to any person in respect of any rights or obligations
         to or in respect of any person in connection with or pursuant to this
         deed poll, whether present or future, actual or contingent, accrued or
         otherwise.

5.       GENERAL

5.1      The Company shall comply with the terms of this deed poll and shall
         observe and perform the provisions of this deed poll which shall be
         binding on the Company and Ribotargets and all persons claiming through
         or under them respectively.

5.2      This deed poll is governed by and shall be construed in accordance with
         English law.

5.3      The Courts of England shall have exclusive jurisdiction to hear and
         decide any suit, action or proceeding and to settle any disputes which
         may arise in connection with this deed poll.

IN WITNESS of which this deed poll has been executed and has been delivered on
the date which appears first above.


                                       4
<PAGE>



                                   SCHEDULE 1

                                   THE BUDGET


<TABLE>
<CAPTION>
                                                          ACTUAL
                                                         JAN YTD    FEBRUARY    MARCH     APRIL      TOTAL
                                                         -------    --------    -----     -----      -----

<S>                                                     <C>          <C>       <C>       <C>      <C>
Internal Costs
Corporate                                                  3,516        402       419       645      4,983
Directorate                                                3,229        410     2,788       279      6,706  (Additional Pound
Research                                                   1,398        162       177       239      1,976  Sterling 2mil of
Business Development                                         353         25        30        68        476  costs relating to Offer)
Development                                                2,018        253       274       558      3,103
                                                          ------      -----     -----     -----     ------
Total Internal Costs                                      10,514      1,252     3,688     1,790     17,244
                                                          ------      -----     -----     -----     ------


Research Projects                  Actual                     69        51       297        416
Business Development Projects      Projects put together   4,804         21        21        19      4,865
Development Projects                                                    475     2,007     1,224      3,706
Genesoft Costshare                                                        0         0     (295)      (295)
                                                          ------      -----     -----     -----     ------
External Costs research projects                           4,804        565     2,079     1,245      8,692
                                                          ------      -----     -----     -----     ------

                                                          ======      =====     =====     =====     ======
Total Operating Expenditure                               15,318      1,817     5,767     3,035     25,936
                                                          ======      =====     =====     =====     ======
</TABLE>




                                       5
<PAGE>

                                   SIGNATORIES



EXECUTED as a deed by                        )        /s/   Timothy Edwards
BRITISH BIOTECH PLC                          )        Director
acting by                                    )
and                                          )        /s/   A J Weir
                                                      Director/Secretary



                                       6









<PAGE>

                                  UNDERTAKINGS
                  RELATING TO THE OFFER BY BRITISH BIOTECH PLC
                          FOR RIBOTARGETS HOLDINGS PLC


                              DATED 21st MARCH , 2003


                                  THE OFFEREES
                               NAMED IN SCHEDULE 1

                                 THE EXECUTIVES

                                       AND

                               BRITISH BIOTECH PLC




                                 ALLEN & OVERY

                                     London




<PAGE>



                                    CONTENTS

<TABLE>
<CAPTION>
CLAUSE                                                                       PAGE
------                                                                       ----
<S>                                                                         <C>
1.       Interpretation.......................................................1
2.       Undertakings and undertaking to accept the Offer.....................2
3.       Undertaking to make the Offer; Option Holders........................4
4.       Completion...........................................................4
5.       Loans and Guarantees.................................................6
6.       Warranties and Undertakings..........................................6
7.       Lock-up of Consideration Shares......................................7
8.       Confidentiality......................................................7
9.       Notices..............................................................8
10.      Further Assurances...................................................8
11.      Assignments..........................................................8
12.      General..............................................................9
13.      Whole Agreement......................................................9
14.      Governing Law.......................................................10

SCHEDULE

1.       The Offerees........................................................11
2.       The Company.........................................................18
3.       The Subsidiary......................................................19
4.       Warranties..........................................................20
5.       Lock-up of Consideration Shares.....................................23
6.       Pre-Completion......................................................25
7.       British Biotech Balance Sheet.......................................28
8.       Ribotargets Balance Sheet...........................................29
9.       Interpretation......................................................30


Signatories..................................................................35
</TABLE>



<PAGE>


THIS UNDERTAKING is executed as a deed on 21st March, 2003 BETWEEN:

(1)      THE PERSONS whose names and addresses are set out in column A of the
         schedule headed "The Offerees" (each an OFFEREE and together the
         OFFEREES);

(2)      Simon Sturge (MR STURGE) and Susan Lowther (each an EXECUTIVE and
         together the EXECUTIVES), both of Granta Park, Abington, Cambridge, CB1
         6GB; and

(3)      BRITISH BIOTECH PLC (registered number 2304992) whose registered office
         is at Thames Court, Watlington Road, Oxford, Oxfordshire OX4 6LY (the
         OFFEROR).

         BACKGROUND:

(A)      Ribotargets Holdings plc (the COMPANY) is a public company limited by
         shares short particulars of which are set out in the schedule headed
         "The Company".

(B)      The Offerees are legally and beneficially or are beneficially entitled
         to sell the Existing Ribotargets Shares which, together with the Apax
         Shares, comprise all the issued share capital of the Company.

(C)      Pursuant to the Contribution Deed, the Relevant Investors have agreed
         to subscribe for New Ribotargets Shares at or prior to Completion.

(D)      The Offeror intends to make an offer (the OFFER) to acquire the whole
         of the issued and to be issued share capital of the Company on the
         terms and subject to the conditions set out in the drafts of the offer
         document (the OFFER DOCUMENT) and the form of acceptance (the FORM OF
         ACCEPTANCE), each in the Agreed Form.

(E)      The Offerees have entered into a form of waiver on or before the date
         of this document, pursuant to which each Offeree has consented to the
         application to the Panel on Takeovers and Mergers for a waiver of the
         Code in connection with the Offer.

IT IS AGREED as follows:

1.       INTERPRETATION

1.1      In addition to terms defined elsewhere in this undertaking, the
         definitions and other provisions in the schedule headed
         "Interpretation" apply throughout this undertaking unless the contrary
         intention appears.

1.2      In this undertaking, unless the contrary intention appears, a reference
         to a clause, subclause or schedule is a reference to a clause,
         subclause or schedule of this undertaking. The schedules and the
         recitals form part of this undertaking.

1.3      The headings in this undertaking do not affect its interpretation.

1.4      All warranties, representations, covenants, indemnities, agreements and
         obligations given or to be entered into by more than one person in this
         undertaking shall be given or entered into severally (and not jointly).

                                       1
<PAGE>

2.       UNDERTAKINGS AND UNDERTAKING TO ACCEPT THE OFFER

2.1      In consideration of the Offeror agreeing (subject to the conditions set
         out in this undertaking) to make the Offer, each of the Offerees
         undertakes, agrees, warrants and covenants to and with the Offeror on
         the terms set out below in this undertaking.

2.2      Each of the Offerees undertakes, agrees, warrants and covenants to and
         with the Offeror in the following terms:

         (a) it is the beneficial owner of those of the Ribotargets Shares set
             out opposite its name in columns (B), (C) and (D) of the schedule
             headed "The Offerees", and in the case of Apax Europe V-A, L.P.,the
             Apax Shares;

         (b) in the case of the Relevant Investors only, it will at Completion
             be the beneficial owner of the New Ribotargets Shares set out
             opposite its name in column (E) of the schedule headed "The
             Offerees";

         (c) it has all necessary authority to accept (or procure the acceptance
             of) the Offer in respect of all the Ribotargets Shares beneficially
             owned by it and to transfer (or procure the transfer of) all the
             Ribotargets Shares beneficially owned by it free from all liens,
             charges and Encumbrances and together with all rights attaching to
             them;

         (d) subject to clause 2.5, it will accept (or procure the acceptance
             of) the Offer in respect of all the Existing Ribotargets Shares and
             New Ribotargets Shares beneficially owned or to be beneficially
             owned by it and deliver (or procure the delivery of) duly completed
             Form(s) of Acceptance, together with the share certificate(s)
             and/or other document(s) of title and/or evidence of authority in
             accordance with the terms of the Offer, not later than 3.00 p.m. on
             the fifth Business Day after despatch of the Offer Document in
             respect of Existing Ribotargets Shares, and not later than Escrow
             Completion in the case of New Ribotargets Shares;

         (e) unless and until the Offer is withdrawn or terminated, it will not
             (or will procure that the registered holder will not) without the
             prior written consent of the Offeror:

             (i)    sell, transfer, charge, pledge or grant any option over or
                    otherwise dispose of any of the Existing Ribotargets Shares
                    and New Ribotargets Shares beneficially owned or to be
                    beneficially owned by it or any interest in any of the
                    Existing Ribotargets Shares and New Ribotargets Shares
                    beneficially owned or to be beneficially owned by it except
                    to the Offeror under the Offer; or

             (ii)   accept any other offer in respect of any of the Existing
                    Ribotargets Shares and New Ribotargets Shares beneficially
                    owned or to be beneficially owned by it (whether it is
                    conditional or unconditional and irrespective of the means
                    by which it is to be implemented); or

             (iii)  subject to subclause 2.5, withdraw or procure or permit the
                    withdrawal of the acceptances referred to in subclause
                    2.2(d) above in respect of any of the Ribotargets Shares
                    beneficially owned by it;

         (f) it has not dealt, nor has any person on its behalf dealt, in
             British Biotech Ordinary Shares during the period of 12 months
             prior to the date of this undertaking, except as disclosed in Part
             VIII of the Circular and Listing Particulars;



                                       2
<PAGE>

         (g) pending Completion, it will not nor will any person on its behalf
             deal in existing British Biotech Ordinary Shares after the date of
             this undertaking without the prior written consent of the Offeror;

         (h) it will, at its own cost and expense, execute and do (or procure to
             be executed and done by any other necessary party (other than the
             Offeror)) all such deeds, documents, acts and things as the Offeror
             may reasonably require in order to vest any of the Existing
             Ribotargets Shares and New Ribotargets Shares beneficially owned by
             it in the Offeror or its assignee. Notwithstanding the obligations
             of the Offerees under this sub-paragraph, the Offeror shall pay any
             stamp duty in connection with the vesting of the Existing
             Ribotargets Shares and New Ribotargets Shares in the Offeror or its
             assignee; and

         (i) each Offeree acknowledges and agrees for the benefit of the Company
             as well as the Offeror that the issue and allotment to it or its
             nominee of the Consideration Shares in accordance with the Offer
             Document will represent the total consideration payable by the
             Offeror to it in respect of the transfer of the Ribotargets Shares
             beneficially owned by such Offeree under the Offer and,
             notwithstanding the rights attaching to the Ribotargets Shares, the
             allocation of the Consideration Shares among the Offerees as
             specified in the Offer Document is a matter for the Offerees alone
             and the Offeror shall not be responsible for determining the
             allocation of the Consideration Shares among the Offerees or the
             registered holders of the Ribotargets Shares.

2.3      Each Offeree waives and will procure the waiver of all rights of
         pre-emption which it or its nominee may have (whether under a Group
         Company's constitutional documents or otherwise) in respect of the
         proposed transfer to the Offeror of the Ribotargets Shares or any of
         them.

2.4      Each of the Executives shall procure the delivery to the Offeror, not
         later than 5 Business Days after 31st March, 2003, of the Ribotargets
         Balance Sheet satisfactory to the Offeror, together with such
         supporting information as the Offeror may reasonably require,
         demonstrating that the Ribotargets Net Working Capital was not less
         than Pound Sterling8,200,000.

2.5      Acceptances of the Offer will be deemed to be withdrawn if the Offeror:

         (a) does not deliver to the Company's Solicitors, not later than 5
             Business Days after 31st March, 2003, the British Biotech Balance
             Sheet satisfactory to an Investor Majority, together with such
             supporting information as an Investor Majority may reasonably
             require, demonstrating that the British Biotech Net Working Capital
             was not less than Pound Sterling23,500,000;

         (b) is in material breach of any obligation on its part under the
             Covenant Deed and, where that breach is capable of remedy, it is
             not remedied to the reasonable satisfaction of an Investor
             Majority.

         If any acceptances of the Offer are withdrawn or deemed withdrawn in
         accordance with this subclause, all the other clauses of this
         undertaking, except for this subclause, the clause headed
         "Confidentiality" and the clauses after it, together with the
         provisions of the clause and schedule headed "Interpretation", shall
         lapse and cease to have effect.

                                       3
<PAGE>

3.       UNDERTAKING TO MAKE THE OFFER; OPTION HOLDERS

3.1      The Offeror undertakes to each Offeree to make the Offer on the terms
         and conditions set out in the Offer Document immediately upon the
         conditions set out in subclause 3.2 having been satisfied.

3.2      The making of the Offer is conditional on:

         (a) the delivery to the Offeror of:

             (i)    a copy of the duly executed Contribution Deed (certified by
                    the Company Secretary of the Company); and

             (ii)   the Termination Deed duly executed by the Company; and

         (b) the delivery by the Offerees to the Company of the Selling Notice
             duly executed by each of the Offerees and the registered holders of
             the Existing Ribotargets Shares.

3.3      The Executives shall procure that the Letter to Option Holders is
         delivered by the Company to all members of the Ribotargets Option
         Schemes as soon as reasonably practicable after the Offer has been
         made.

3.4      Each of the Executives shall use reasonable endeavours to procure (so
         far as it is lawfully able to procure) that the Conditions specified in
         subparagraphs (h) and (i) of Part A of Appendix I to the Offer Document
         are satisfied on or before 30th April, 2003 (the LONG STOP DATE). If
         all the Conditions are not fulfilled or, where permitted, waived on or
         before the Long Stop Date, or such other date as the parties may agree,
         except for this subclause, the clause headed "Confidentiality" and the
         clauses after it, together with the provisions of the clause and
         schedule headed "Interpretation", all the other clauses of this
         undertaking shall lapse and cease to have effect.

4.       COMPLETION

4.1      Provided that the Conditions have been satisfied or, where permitted,
         waived (other than the Escrow Condition and the Conditions in
         paragraphs 1(e), (f) and (g) of Part A of Appendix I to the Offer
         Document), the Offerees agree that Completion will take place in two
         stages as follows:

         (a) Escrow Completion will take place at the offices of the Offeror's
             Solicitors (or at such other place as the parties may agree) on the
             Business Day prior to that on which the Escrow Condition is
             expected to be satisfied. At Escrow Completion, all matters and
             things required to be done under subclause 4.4 below will be duly
             performed but all actions and documents will be held in escrow so
             that their terms do not come into force and effect until Completion
             and subject as set out in subclause 4.3; and

         (b) subject to Escrow Completion having taken place in accordance with
             the terms set out above, Completion shall only be conditional upon
             satisfaction of the Escrow Condition and satisfaction or waiver of
             the Conditions in paragraphs 1(e), (f) and (g) of Part A of
             Appendix I to the Offer Document and shall take place immediately
             upon their satisfaction or, where permitted, waiver. Forthwith upon
             Completion taking place all actions, deeds, agreements and
             documents delivered at Escrow Completion shall be released
             therefrom and dated such that their terms shall come into immediate
             full force and effect.



                                       4
<PAGE>

4.2      Pending Completion (and whether or not the Conditions are satisfied or,
         where permitted, waived) the provisions of the schedule headed
         "Pre-Completion" shall apply.

4.3      If Completion does not occur as a result of the Offeror exercising its
         right to withdraw the Offer in any of the circumstances mentioned in
         paragraph 1 of Part B of Appendix I to the Offer Document or otherwise,
         or if this Offer otherwise lapses in accordance with its terms, any
         agreements or documents executed (including transfers of Ribotargets
         Shares or allotments of Consideration Shares) shall be deemed to be of
         no effect and all documents, agreements, papers and other things
         delivered pursuant to this clause or in anticipation of Completion
         shall forthwith be returned to the relevant person.

4.4      At Completion:

         (a) the Relevant Investors shall subscribe for additional B Ordinary
             Shares in accordance with the terms of the Contribution Deed;

         (b) the Executives shall procure that a board meeting of the Company is
             held at which, in accordance with article 7.5.4 of the Articles,
             the directors of the Company shall authorise a person to execute
             and deliver on behalf of each Defaulting Member (if any) the
             necessary transfer(s) as the Offeror may decide to the Offeror of
             any Ribotargets Shares;

         (c) each Offeree shall procure the delivery by it to the Offeror of:

             (i)    a duly executed transfer in favour of the Offeror or its
                    nominee(s) of all the Ribotargets Shares beneficially owned
                    by it other than the Apax Shares; and

             (ii)   the share certificates representing all the Ribotargets
                    Shares other than the Apax Shares (or an express indemnity
                    satisfactory to the Offeror in the case of any found to be
                    missing);

         (d) the Executives shall procure the delivery to the Offeror of:

             (i)    the certificate of incorporation, common seal (if any),
                    minute books, statutory registers and share certificate
                    books of each Group Company;

             (ii)   the resignations of the directors (except Mr Sturge) and the
                    secretary of each Group Company in the Agreed Form; and

             (iii)  copies (certified by the Company Secretary of the relevant
                    Group Company) of the minutes of the meetings referred to in
                    paragraphs (e) and (f) below;

         (e) the Executives shall procure that a board meeting of each Group
             Company is held at which it is resolved that (subject only to the
             satisfaction of the Escrow Condition):

             (i)    such persons as the Offeror nominates are appointed as
                    additional directors and the secretary of that Group
                    Company;

             (ii)   its registered office is changed to such address as the
                    Offeror may require ;

             (iii)  the transfers referred to in subclause 4.4(c)(i) above
                    (subject only to their being duly stamped, which shall be at
                    the cost of the Offeror) are approved for registration; and



                                       5
<PAGE>

             (iv)   its bank mandates are revised in such manner as the Offeror
                    may require.

5.       LOANS AND GUARANTEES

5.1      Each Offeree shall procure that on or before Completion all
         indebtedness due from it or any of its subsidiaries or subsidiary
         undertakings to any Group Company is satisfied in full without payment
         of interest.

5.2      Each Offeree shall procure that on Completion each Group Company is
         released from all guarantees and indemnities given by any Group Company
         in respect of the liabilities of such Offeree or any of its
         subsidiaries or subsidiary undertakings.

6.       WARRANTIES AND UNDERTAKINGS

6.1      On the basis that in making the Offer the Offeror shall not, and shall
         not be entitled to, rely on any representation, warranty, collateral
         contract or other assurance except those set out in this undertaking,
         the Offer Document and Form of Acceptance:

         (a) each Offeree warrants to the Offeror in the terms of the Offerees'
             Warranties in relation to itself only;

         (b) each US Offeree warrants to the Offeror in the terms of the US
             Offerees' Warranties in relation to itself only; and

         (c) Mr Sturge warrants to the Offeror in the terms of the Executive's
             Warranties,

         in each case as at the date of this undertaking and as at Completion.

6.2      The Offerees and Mr Sturge acknowledge that the Offeror has agreed to
         make the Offer in reliance on the warranties and undertakings on their
         part set out in this undertaking.

6.3      Each of the Warranties set out in the several paragraphs of the
         schedule headed "Warranties" is separate and independent and none of
         the Warranties shall be treated as qualified by any actual or
         constructive knowledge on the part of the Offeror.

6.4      Each US Offeree agrees that so long as the Consideration Shares remain
         "restricted securities" (as defined in Rule 144(a)(3) under the
         Securities Act), it will not (on its own behalf or on behalf of anyone
         else) offer, sell, transfer, pledge or otherwise dispose of the
         Consideration Shares except:

         (a) to the Offeror;

         (b) pursuant to an effective registration statement filed with the US
             Securities and Exchange Commission (it being acknowledged that the
             Offeror is under no obligation to file such a registration
             statement);

         (c) in an offshore transaction meeting the requirements of Rule 903 or
             Rule 904 of Regulation S under the Securities Act;

         (d) in a transaction exempt from registration under the Securities Act
             under Rule 144 (if available); or



                                       6
<PAGE>

         (e) in another transaction that is exempt from the registration
             requirements of the Securities Act to a transferee who has
             furnished such certificates and opinions of counsel as the Offeror
             may request,

         and in the case of subclauses 6.4(d) through (e) above, in compliance
         with any applicable securities laws of any state of the United States.
         Each US Offeree acknowledges that any Consideration Shares issued to it
         will be issued in certificated form bearing a legend to the effect of
         the foregoing restrictions in this clause 6.4.

6.5      Each US Offeree acknowledges that the Offeror will rely on the truth
         and accuracy of the certificates and opinions referred to in clause
         6.4(e) and agrees that if it becomes aware (without any obligation to
         make any enquiry in the case of the representations and warranties
         given by a purchaser of its Consideration Shares) that any of the
         representations and warranties made by it or by a purchaser in
         connection with the sale by it of any Consideration Shares are no
         longer accurate, the relevant US Offeree shall promptly notify the
         Offeror.

6.6      Each US Offeree agrees that in the event it transfers the Consideration
         Shares such US Offeree will notify any purchaser of the Consideration
         Shares from it of the resale restrictions relating to the Consideration
         Shares set out in clause 6.4.

6.7      Each US Offeree understands that in connection with any transfer of the
         Consideration Shares by it the Offeror may request, and if so requested
         such US Offeree will furnish, such certificates or other information as
         it may reasonably require to confirm that any such transfer complies
         with the restrictions set out in clause 6.4.

6.8      Each US Offeree agrees that so long as any of the Consideration Shares
         are "restricted securities" within the meaning of Rule 144(a)(3) under
         the Securities Act, it will not deposit such Consideration Shares into
         any unrestricted depositary receipt facility established or maintained
         by a depositary bank.

7.       LOCK-UP OF CONSIDERATION SHARES

         Subject to Completion, the Offerees shall observe and perform those
         provisions of the schedule headed "Lock-up of Consideration Shares" as
         are expressed to be observed and performed by each of them.

8.       CONFIDENTIALITY

8.1      Subject to clause 8.2 and the issue of the Press Release, no Offeree
         shall make, or permit any person connected with it to make, or permit
         any other member of its Offeree's Group to make any announcement or
         disclose any confidential information concerning the Offer, this
         undertaking or any ancillary matter before, on or after Completion.

8.2      Nothing in this clause prevents any announcement being made or any
         confidential information being disclosed:

         (a) with the written approval of the Offeror which in the case of any
             announcement shall not be unreasonably withheld or delayed; or

         (b) to the extent required by law or any competent tax or regulatory
             body to which a party is or may become subject, but a party
             required to disclose any confidential information shall promptly
             notify the Offeror to whom the information relates (where
             practicable and lawful to do so), before disclosure occurs and
             co-operate with those other parties regarding the timing and
             content of such disclosure or any action which


                                       7
<PAGE>


                  those other parties may reasonably elect to take to challenge
                  the validity of such requirement.

8.3      Nothing in this clause prevents disclosure of confidential information
         by any party:

         (a) to the extent that the information is in or comes into the public
             domain other than as a result of a breach of any undertaking or
             duty of confidentiality by any person; or

         (b) to that party's professional advisers, auditors or bankers, but
             before any disclosure to any such person the relevant party shall
             procure that he is made aware of the terms of this clause and shall
             use its reasonable endeavours to procure that each such person
             adheres to those terms as if he were bound by the provisions of
             this clause.

9.       NOTICES

9.1      Any notice or other formal communication given under this undertaking
         must be in writing and may be delivered, or sent by post to the party
         to be served at its address appearing in this undertaking or at such
         other address as it may notify to the other parties under this clause.
         Any notice or other document sent by post shall be sent by prepaid
         first class recorded delivery post (if within the United Kingdom) or by
         prepaid airmail (if its destination is elsewhere).

9.2      Any notice or other communication shall be deemed to have been given:

         (a) if delivered, at the time of delivery; or

         (b) if sent by post, at 10.00 a.m. on the second Business Day after it
             was put into the post.

9.3      In proving the giving of a notice or other formal communication it
         shall be sufficient to prove that delivery was made or that the
         envelope containing the communication was properly addressed and
         posted, either by prepaid first class recorded delivery post or by
         prepaid airmail as the case may be.

10.      FURTHER ASSURANCES

         On or after Completion each Offeree shall, at its own cost and expense,
         execute and do (or procure to be executed and done by any other
         necessary person) all such deeds, documents, acts and things as the
         Offeror may from time to time require in order to vest any of the
         Ribotargets Shares beneficially owned by it, in respect of which the
         Offer is accepted, in the Offeror or its assignee or as otherwise may
         be necessary to give full effect to this undertaking. Notwithstanding
         this clause, the Offerees shall not be liable to pay stamp duty in
         connection with the vesting of their Ribotargets Shares in respect of
         which the Offer is accepted, in the Offeror or its assignee.


11.      ASSIGNMENTS

         None of the rights or obligations of the Offerees under this
         undertaking may be assigned or transferred without the consent of all
         the parties.



                                       8
<PAGE>

12.      GENERAL

12.1     The receipt of the Company's Solicitors for any document to be
         delivered to an Offeree or Executive shall discharge the Offeror's
         obligation to deliver it to that Offeree or Executive.

12.2     Each of the obligations, Warranties and undertakings set out in this
         undertaking (excluding any obligation which is fully performed at
         Completion) shall continue in force after Completion and shall not be
         affected by the waiver of any Condition or notice given by the Offeror
         in respect of any Condition.

12.3     The Offeror may release or compromise in whole or in part the liability
         of any of the Offerees or Executives under this undertaking or grant
         any time or indulgence without affecting the liability of any other
         Offeree or Executive.

12.4     In accordance with article 4.1(a) and 9 of the Articles, each Offeree
         hereby consents to the transfer of the Ribotargets Shares pursuant to
         the terms of the Offer.

12.5     In accordance with clause 10.1 of the Ribotargets Shareholders'
         Agreement, the Investor Majority hereby consent to the transfer of the
         Ribotargets Shares pursuant to the terms of the Offer.

12.6     Time is not of the essence in relation to any obligation under this
         undertaking unless:

         (a) time is expressly stated to be of the essence in relation to that
             obligation; or

         (b) one party fails to perform an obligation by the time specified in
             this undertaking and another party serves a notice on the
             defaulting party requiring it to perform the obligation by a
             specified time and stating that time is of the essence in relation
             to that obligation.

12.7     This undertaking may be executed in any number of counterparts. This
         has the same effect as if the signatures on the counterparts were on a
         single copy of this undertaking.

12.8     The rights of each party under this undertaking:

         (a) may be exercised as often as necessary;

         (b) are cumulative and not exclusive of rights and remedies provided by
             law; and

         (c) may be waived only in writing and specifically.

         Delay in exercising or non-exercise of any such right is not a waiver
         of that right.

12.9     A person who is not a party to this undertaking may not enforce any of
         its terms under the Contracts (Rights of Third Parties) Act 1999 except
         where a term in this undertaking is expressed to be for the benefit of
         such person.

13.      WHOLE AGREEMENT

13.1     This undertaking, and the documents referred to in it and in the Offer
         Document, and the Covenant Deed contain the whole agreement between the
         parties relating to the Offer and the transactions contemplated by this
         undertaking and supersede all previous agreements, whether oral or in
         writing, between the parties relating to these transactions.

                                       9
<PAGE>

13.2     Each Offeree acknowledges that in accepting the Offer, and agreeing to
         enter into this undertaking it has not relied or will not rely on any
         representation, warranty, collateral contract or other assurance
         (except, if any, those set out in this undertaking and the documents
         referred to in it) made by or on behalf of any other party before the
         signature of this undertaking. Each Offeree waives all rights and
         remedies which, but for this subclause, might otherwise be available to
         it in respect of any such representation, warranty, collateral contract
         or other assurance.

13.3     Nothing in the preceding subclause limits or excludes any liability for
         fraud.

14.      GOVERNING LAW

14.1     This undertaking is governed by English law.

14.2     The English courts have exclusive jurisdiction to settle any dispute
         arising out of or in connection with this undertaking and the parties
         submit to the exclusive jurisdiction of the English courts.

14.3     Each Offeree whose registered office or principal private residence is
         not in England and Wales irrevocably appoints Mitre Secretaries Limited
         of Mitre House, 160 Aldersgate Street, London EC1A 4DD as its agent in
         England for service of process, other than those Offerees in the
         schedule headed "The Offerees" numbered 13-24 (who shall appoint Apax
         Partners Ltd of 1 Portland Place, London W1B 1PT) and the Offeree
         numbered 26 (who shall appoint JP Morgan Partners Europe Limited, 14th
         Floor, 125 London Wall, London, EC2Y 5AJ).

14.4     Each Offeree waives any right it may have to a jury trial of any claim
         or cause of action in connection with this undertaking. This
         undertaking may be filed as a written consent to trial by court.

AS WITNESS this undertaking has been executed by the parties (or their duly
authorised representatives) as a deed and has been delivered on the date stated
at the beginning of this undertaking.




                                       10
<PAGE>





                                   SCHEDULE 1

                                  THE OFFEREES





<TABLE>
<CAPTION>
               (A)                                 (B)                (C)                   (D)                  (E)

                                                 NUMBER OF         NUMBER OF A         NUMBER OF B           NUMBER OF NEW
     NAME AND ADDRESS OF OFFEREE              ORDINARY SHARES    ORDINARY SHARES     ORDINARY SHARES      RIBOTARGETS SHARES
                                                                                                           TO BE SUBSCRIBED
     ---------------------------              ---------------    ---------------     ---------------    ------------------------
<S>                                              <C>               <C>                 <C>                    <C>
1.   3i Group plc                                       --           1,472,779            683,761                257,255
     91 Waterloo Road
     London SE1 8XP

2.   3i Bioscience Investment Trust plc                 --                  --            170,940                 64,250
     91 Waterloo Road
     London SE1 8XP

3.   Advent VCT plc                                     --             841,590            166,667                     --
     25 Buckingham Gate
     London SW1E 6LD

4.   Advent Private Equity Fund III 'A'                 --                  --            486,573                183,046
     25 Buckingham Gate
     London SW1E 6LD
</TABLE>

                                       11
<PAGE>

<TABLE>
<CAPTION>
               (A)                                 (B)                (C)                   (D)                  (E)

                                                 NUMBER OF         NUMBER OF A         NUMBER OF B           NUMBER OF NEW
     NAME AND ADDRESS OF OFFEREE              ORDINARY SHARES    ORDINARY SHARES     ORDINARY SHARES      RIBOTARGETS SHARES
                                                                                                           TO BE SUBSCRIBED
     ---------------------------              ---------------    ---------------     ---------------    ------------------------
<S>                                              <C>               <C>                 <C>                    <C>
5.   Advent Private Equity Fund III 'B'                 --                  --            238,423                 89,694
     25 Buckingham Gate
     London SW1E 6LD

6.   Advent Private Equity Fund III 'C'                 --                  --             66,508                 25,020
     25 Buckingham Gate
     London SW1E 6LD

7.   Advent Private Equity Fund III 'D'                 --                  --            130,819                 49,213
     25 Buckingham Gate
     London SW1E 6LD

8.   Advent Private Equity Fund III                     --                  --             18,823                  7,081
     GmbH & Co KG
     25 Buckingham Gate
     London SW1E 6LD

9.   Advent Private Equity Fund III                     --                  --             15,686                  5,901
     Affiliates
     c/o 25 Buckingham Gate
     London  SW1E 6LD

10.  Advent Management III Limited                      --                  --              4,706                  1,770
     Partnership
     25 Buckingham Gate
     London  SW1E 6LD
</TABLE>



                                       12
<PAGE>

<TABLE>
<CAPTION>
               (A)                                 (B)                (C)                   (D)                  (E)

                                                 NUMBER OF         NUMBER OF A         NUMBER OF B           NUMBER OF NEW
     NAME AND ADDRESS OF OFFEREE              ORDINARY SHARES    ORDINARY SHARES     ORDINARY SHARES       RIBOTARGETS SHARES
                                                                                                            TO BE SUBSCRIBED
     ---------------------------              ---------------    ---------------     ---------------    ------------------------
<S>                                              <C>               <C>                 <C>                    <C>
11.  Alan Driver                                     5,700                  --                 --                     --
     5 Kohat Road
     London
     SW19 8LD

12.  Alpinvest Holding NV                               --             625,000            420,438                158,190
     c/o NIB Capital Private Equity NV
     Jachthavenweg 118, 1081 KJ
     The Netherlands

13.  Apax UK V-A, L.P.                                  --           1,854,368                 --                     --
     1 Portland Place
     London W1B 1PT

14.  Apax UK V-B, L.P.                                  --           1,923,995                 --                     --
     1 Portland Place
     London W1B 1PT

15.  Apax Europe V-A, L.P.                              --                  --          1,452,264                546,370
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D

16.  Apax Europe V-B, L.P.                              --                  --            261,337                 98,320
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D
</TABLE>



                                       13
<PAGE>

<TABLE>
<CAPTION>
               (A)                                 (B)                (C)                   (D)                  (E)

                                                 NUMBER OF         NUMBER OF A         NUMBER OF B           NUMBER OF NEW
     NAME AND ADDRESS OF OFFEREE              ORDINARY SHARES    ORDINARY SHARES     ORDINARY SHARES      RIBOTARGETS SHARES
                                                                                                           TO BE SUBSCRIBED
     ---------------------------              ---------------    ---------------     ---------------    ------------------------
<S>                                              <C>               <C>                 <C>                    <C>
17.  Apax Europe V-C GmbH & Co. KG                      --                  --            148,743                 55,960
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D

18.  Apax Europe V-D, L.P.                              --                  --            195,365                 73,500
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D

19.  Apax Europe V-E, L.P.                              --                  --            194,688                 73,245
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D

20.  Apax Europe V-F, C.V.                              --                  --             34,235                 12,880
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D

21.  Apax Europe V-G, C.V.                              --                  --             34,235                 12,880
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D
</TABLE>


                                       14
<PAGE>

<TABLE>
<CAPTION>
               (A)                                 (B)                (C)                   (D)                  (E)

                                                 NUMBER OF         NUMBER OF A         NUMBER OF B           NUMBER OF NEW
     NAME AND ADDRESS OF OFFEREE              ORDINARY SHARES    ORDINARY SHARES     ORDINARY SHARES      RIBOTARGETS SHARES
                                                                                                           TO BE SUBSCRIBED
     ---------------------------              ---------------    ---------------     ---------------    ------------------------
<S>                                              <C>               <C>                 <C>                    <C>
22.  Apax Europe V-1 L.P.                               --                  --              1,090                    410
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D

23.  Apax Europe V-2 L.P.                               --                  --              1,090                    410
     13-15 Victoria Road
     St Peter Port
     Guernsey GY1 32D

24.  AP V GmbH & Co KG                                  --                  --            258,117                 97,105
     Nussbaumstrasse 8
     80336 Munich
     Germany

25.  Caduceus Private Investment LLP                    --                  --            246,941                 92,970
     c/o Orbimed Advisors
     767 3rd Avenue
     New York NY 10017

26.  J.P. Morgan Partners (BHCA) Limited                --                  --          1,282,052                482,340
     1221 Avenue of the Americas
     New York 10020
     USA

27.  Medical Research Council                      412,500                  --                 --                     --
     20 Park Crescent
     London W1N 4AL
</TABLE>

                                       15
<PAGE>

<TABLE>
<CAPTION>
               (A)                                 (B)                (C)                   (D)                  (E)

                                                 NUMBER OF         NUMBER OF A         NUMBER OF B           NUMBER OF NEW
     NAME AND ADDRESS OF OFFEREE              ORDINARY SHARES    ORDINARY SHARES     ORDINARY SHARES       RIBOTARGETS SHARES
                                                                                                            TO BE SUBSCRIBED
     ---------------------------              ---------------    ---------------     ---------------    ------------------------
<S>                                              <C>               <C>                 <C>                    <C>
28.  Orbimed Associates LLC                             --                  --              5,140                  1,950
     c/o Orbimed Advisors
     767 3rd Avenue
     New York NY 10017

29.  PW Juniper Crossover Fund LLC                      --                  --            116,508                 43,830
     c/o Orbimed Advisors
     767 3rd Avenue
     New York NY 10017

30.  Quester VCT 2 Plc                                  --             187,500            196,765                     --
     29 Queen Anne's Gate
     London  SW7H 9BY

31.  Quester VCT 3 Plc                                  --             187,500            196,765                     --
     29 Queen Anne's Gate
     London  SW7H 9BY

32.  Rendex N.V                                         --             625,000                 --                     --
     Straalstraat 2
     B-2170 Antwerpen
     Belgium

33.  Simon Sturge                                   75,000                  --                 --                     --
     Granta Park
     Abington
     Cambridge CB1 6GB
</TABLE>


                                       16
<PAGE>

<TABLE>
<CAPTION>
               (A)                                 (B)                (C)                   (D)                  (E)

                                                 NUMBER OF         NUMBER OF A         NUMBER OF B           NUMBER OF NEW
     NAME AND ADDRESS OF OFFEREE              ORDINARY SHARES    ORDINARY SHARES     ORDINARY SHARES      RIBOTARGETS SHARES
                                                                                                            TO BE SUBSCRIBED
     ---------------------------              ---------------    ---------------     ---------------    ------------------------
<S>                                              <C>               <C>                 <C>                    <C>
34.  Professor Colin S Goodchild                    20,583                  --                 --                     --
     38 Somers Avenue
     Malvern
     Victoria 3144
     Australia

35.  Monash Commercial Proprietary Limited           7,917                  --                 --                     --
     Administration Building 3B
     Monash University
     Monash
     Victoria 3800
     Australia

36.  Dr Ray Nadeson                                  3,167                  --                 --                     --
     PO Box 2297,
     Prahran
     Victoria 3181
     Australia

37.  Biocomm Services Proprietary Limited            1,666                  --                 --                     --
     Level 6
     350 Collins Street
     Melbourne
     Victoria 3000
     Australia
</TABLE>




                                       17
<PAGE>


                                   SCHEDULE 2

                                   THE COMPANY



<TABLE>
<S>                                  <C>
Name:                                 Ribotargets Holdings plc

Registered number:                    3339154

Registered office:                    Granta Park
                                      Abington
                                      Cambridge
                                      CB1 6GB

Date and place of incorporation:      6th June, 1997 at Companies House, London

Directors:                            Mr J C Benjamin
                                      Mr I F Kent (Chairman)
                                      Dr D J C Knowles
                                      Mrs S D Lowther
                                      Mr P Rattle
                                      Dr J Reffin
                                      Mr S J Sturge
                                      Dr D U'Prichard
                                      Mr C H Samler
                                      Dr B C Ross
                                      Dr H Finch

Secretary:                            Mitre Securities Limited
                                      Mitre House
                                      160 Aldersgate Street
                                      London
                                      EC1A 4DD

Accounting reference date:            31st December

Auditors:                             PricewaterhouseCoopers

Authorised capital:                   3,620,500 Ordinary Shares of 10p each
                                      7,928,630 A Ordinary Shares of 10p each
                                      11,000,007 B Ordinary Shares of 10p each
                                      6,220,057 Unclassified Shares of Pound Sterling1 each

Issued capital:                       526,533 Ordinary Shares of 10p each
                                      7,718,233 A Ordinary Shares of 10p each
                                      3,923,808 B Ordinary Shares of 10p each

</TABLE>


                                       18
<PAGE>

                                   SCHEDULE 3

                                 THE SUBSIDIARY



<TABLE>
<S>                                  <C>
Name:                                 Ribotargets Limited

Registered number:                    3219804

Registered office:                    Granta Park
                                      Abington
                                      Cambridge
                                      CB1 6GB

Date and place of incorporation:      4th September, 1996 at Companies House, Cardiff

Directors:                            Dr D J C Knowles
                                      Mrs S D Lowther
                                      Mr S J Sturge

Secretary:                            Mitre Securities Limited
                                      Mitre House
                                      160 Aldersgate Street
                                      London
                                      EC1A 4DD

Accounting reference date:            31st December

Auditors:                             PricewaterhouseCoopers

Authorised capital:                   100 ordinary shares of Pound Sterling1 each

Issued capital:                       2 ordinary shares of Pound Sterling1 each
</TABLE>



                                       19
<PAGE>

                                   SCHEDULE 4

                                   WARRANTIES

                                     PART 1

                              OFFEREES' WARRANTIES

1.       CAPACITY

(a)      Each Offeree has the requisite power and authority to enter into and
         perform, and has taken all necessary action to authorise the execution
         and performance of, its obligations under this undertaking.

(b)      All consents, approvals, authorisations, orders, registrations,
         clearances and qualifications of or with any court or government agency
         or body having jurisdiction over each Offeree or any stock exchange
         authorities required for the execution and delivery by each Offeree of
         this undertaking to be duly and validly authorised, and required for
         Completion, have been obtained or made by each Offeree and insofar as
         they relate to each Offeree, are in full force and effect.

2.       VALID OBLIGATIONS

         This undertaking constitutes valid and binding obligations of each
         Offeree.

3.       OWNERSHIP OF RIBOTARGETS SHARES

(a)      Each Offeree has not given any option, right to acquire, mortgage,
         charge, pledge, lien or other form of security or encumbrance on, over
         or affecting any of the Ribotargets Shares beneficially owned by it
         (save for the grant of floating charges which have not crystallised)
         and there is no agreement or commitment entered into by it to give or
         create any of the foregoing.

(b)      Each Offeree is entitled to transfer or procure the transfer of the
         full legal and beneficial ownership in the Existing Ribotargets Shares
         beneficially owned by it to the Offeror on the terms set out in the
         Offer.

(c)      On Completion, each Relevant Investor shall be entitled to transfer or
         procure the transfer of the full legal and beneficial ownership in the
         New Ribotargets Shares beneficially owned by it to the Offeror on the
         terms set out in the Offer.

4.       NON-US PERSONS

         Other than the US Offerees, each Offeree is not a US Person and was not
         or will not be in the United States (a) at the time the Offer is made,
         (b) on the date of the execution and delivery of this undertaking, and
         (c) on the date of Completion.

5.       ACCURACY OF INFORMATION

         All statements relating to each Offeree in Part VIII of the Circular
         and Listing Particulars are true and accurate and are not misleading by
         omission or by misstatement in the context in which they are made.



                                       20
<PAGE>

                                     PART 2

                             US OFFEREES' WARRANTIES

Each US Offeree hereby represents, warrants and agrees as follows:

1.       Each US Offeree understands that the Consideration Shares (i) have not
         been and will not be registered under the Securities Act, (ii) are
         being sold to the US Offerees in a transaction exempt from the
         registration requirements of the Securities Act and (iii) are
         "restricted securities" as defined by Rule 144(a)(3) under the
         Securities Act.

2.       Each US Offeree is an institutional "accredited investor" as defined in
         Rule 501(a)(1), (2), (3), (7) or (8) of Regulation D under the
         Securities Act.

3.       Each US Offeree is acquiring the Consideration Shares for its own
         account, for investment purposes only and not with a view to any resale
         or distribution of the Consideration Shares.

4.       Each US Offeree has such knowledge, sophistication and experience in
         financial and business matters as to be capable of evaluating the
         merits and risks of its investment in the Consideration Shares. At the
         present time, each US Offeree is able to bear the economic risk of an
         investment in the Consideration Shares, has adequate means to provide
         for its current and contingent needs, has no need for liquidity with
         respect to an investment in the Ribotargets Shares, and can afford a
         complete loss of such investment.

5.       Each US Offeree has access to such financial and other information
         concerning the Offeror and the Consideration Shares as each US Offeree
         has deemed necessary or desirable in connection with the sale of the
         Consideration Shares, has had adequate time to consider whether to
         accept the Offer and has had the opportunity to ask questions of
         representatives of the Offeror concerning the Offer, the Offeror and
         the Consideration Shares.

6.       Each US Offeree has made its own financial decision in respect of the
         Offer and the Consideration Shares on the basis of its independent
         investigation and appraisal of the business, financial condition,
         prospects, creditworthiness, status and affairs of the Offeror and of
         the Consideration Shares. Each US Offeree has informed itself, to the
         extent that each US Offeree deems appropriate, as to the potential tax
         consequences, legal and regulatory requirements and foreign exchange
         restrictions that may be relevant to the sale of the Consideration
         Shares.


                                     PART 3

                             EXECUTIVE'S WARRANTIES

1.       The Existing Ribotargets Shares, the New Ribotargets Shares and the
         Apax Shares will at Completion constitute the whole of the issued and
         allotted share capital of the Company (other than any shares that may
         be allotted and issued under the Ribotargets Option Schemes).

2.       Other than pursuant to the Ribotargets Option Schemes or the
         Contribution Deed, there is no option or right to subscribe any shares
         in the capital of Ribotargets, and there is no agreement or commitment
         to give or create any of the foregoing.

3.       All consents, approvals, authorisations, orders, registrations,
         clearances and qualifications of or with any court or government agency
         or body having jurisdiction over the Group


                                       21
<PAGE>


         Companies required for Completion have been obtained or made and are in
         full force and effect.

                                       22
<PAGE>




                                   SCHEDULE 5

                         LOCK-UP OF CONSIDERATION SHARES

1.       For the purposes of this schedule:

         (a) DISPOSE shall include any dealings in derivatives referenced to
             British Biotech Ordinary Shares (whether or not involving the
             possibility of delivery of British Biotech Ordinary Shares) and
             which in any case indirectly amounts to a disposal;

         (b) INTEREST shall have the meaning given to it in section 208 of the
             Companies Act 1985 excluding section 209 thereof; and

         (c) QUALIFYING OFFEREE means an Offeree whose beneficial holding of
             Lock-up Shares immediately following Completion amounts to less
             than one per cent. of the aggregate issued ordinary share capital
             of the Offeror immediately following Completion.

2.       Subject to paragraph 8 of this schedule, each Offeree covenants to the
         Offeror that it shall not, and its nominees shall not, save with the
         prior written consent of the Offeror, sell, transfer, mortgage, charge,
         pledge, grant options over or otherwise dispose of or enter into any
         agreement or arrangement (whether or not legally binding) to sell,
         transfer, mortgage, charge, pledge, grant options over or otherwise
         dispose of any of the Consideration Shares allotted to it or its
         nominees (LOCK-UP SHARES) or any direct or indirect interest in any
         such Lock-up Shares, or any rights arising from or attached to any such
         Lock-up Shares, or enter into any contract for differences, swap,
         evidence of indebtedness or other derivatives transaction that changes
         in value or determines value by reference to British Biotech Ordinary
         Shares, or enter into any transaction having the same economic effect
         as any of the foregoing at any time during the period of six calendar
         months following Completion (the INITIAL LOCK-UP PERIOD). British
         Biotech agrees and acknowledges that in determining whether to provide
         its written consent to an Offeree's request to release all or any of
         such Offeree's Lock-up Shares in accordance with this paragraph 2 the
         provisions of paragraph 3 of this schedule shall not be taken into
         consideration.

3.       The board of directors of the Offeror may, at its discretion following
         completion by the Offeror of a corporate transaction other than the
         Offer, release the Offerees from the restriction contained in paragraph
         2 above in respect of up to a maximum aggregate number of Lock-up
         Shares equal to 25% of each Offeree's total Lock-up Shares (RELEASED
         SHARES), provided that any disposal of such Released Shares in the
         Initial Lock-up Period shall be made through the Offeror's nominated
         broker (currently Cazenove & Co. Limited).

4.       Subject to paragraphs 5 and 8 of this schedule, each Offeree covenants
         to the Offeror that during the period of eight calendar months after
         the Initial Lock-up Period has expired (the INTERIM LOCK-UP PERIOD) it
         will:

         (a) notify the Offeror or its nominated broker in writing prior to the
             disposal of any Lock-up Shares; and

         (b) not (and will procure that its nominees do not) dispose of any
             Lock-up Shares other than through the Offeror's nominated broker
             (provided that if an Offeree receives an unsolicited offer to
             acquire Lock-up Shares then the preceding provision of this
             subparagraph (b) shall not apply to a disposal to the person who
             made such offer but


                                       23
<PAGE>


             such Offeree shall be obliged to notify the Offeror's nominated
             broker in writing prior to such disposal).

5.       During the Interim Lock-up Period the Qualifying Offerees shall
         together be entitled to dispose of Lock-up Shares up to a maximum
         aggregate of Lock-up Shares equal to three per cent. of the issued
         ordinary share capital of the Offeror immediately following Completion
         without using the Offeror's nominated broker to effect such disposal.

6.       An Offeree wishing to dispose of any Lock-up Shares during the period
         of six months after the Interim Lock-up Period has expired must consult
         with the Offeror's nominated broker about such disposal for a
         reasonable period of time prior to the proposed disposal, including,
         without limitation, with respect to the method and timing of the
         disposal.

7.       Each Offeree undertakes that prior to the end of the Initial Lock-up
         Period it will not acquire or offer to acquire, or cause another person
         to acquire or offer to acquire any direct or indirect interest in any
         British Biotech Ordinary Shares or enter into any agreement or
         arrangement (whether or not legally binding) or do or omit to do any
         act as a result of which it or any person may acquire any direct or
         indirect interest in any British Biotech Ordinary Shares if the effect
         of such act or omission would be to oblige any person to make a
         mandatory offer for the Offeror under Rule 9 of the Code.

8.       Nothing in this schedule shall prevent:

         (a) a disposal pursuant to a court order;

         (b) a renunciation of a right to subscribe for shares where such right
             is derived from the Lock-up Shares or a failure to take up any such
             right;

         (c) if the Offeror makes an offer to its shareholders to purchase its
             own shares or proposes a scheme of arrangement, a disposal or
             agreement to dispose of any Lock-up Shares to the Offeror pursuant
             to that offer or scheme; or

         (d) an Offeree or its nominee from accepting a general offer made for
             all the issued share capital of the Offeror provided such offer is
             recommended by the board of directors of the Offeror.

9.       The provisions of this schedule shall also apply to any other
         securities for the time being representing or derived from the Lock-up
         Shares (whether by way of consolidation, sub-division, capitalisation
         or rights issue or otherwise), other than any such securities as may be
         acquired for cash by way of rights or other issue, and references in
         this clause to the Lock-up Shares shall be construed accordingly.


                                       24
<PAGE>

                                   SCHEDULE 6

                                 PRE-COMPLETION

1.       ACCESS

         Pending Completion the Executives shall:

         (a) procure that the Offeror, its agents and representatives are given
             full access to the properties and to the books and records of the
             Group Companies during normal business hours on any Business Day
             and on reasonable notice to the Executives; and

         (b) provide such information regarding the businesses and affairs of
             the Group Companies as the Offeror may reasonably request,

         in each case insofar as such access and the provision of such
         information is compatible with competition law and, in particular, does
         not involve access to or the provision of business secrets of any of
         the Group Companies.

2.       CONVERSION OF SHARES

         Pending Completion, each Offeree who is a beneficial owner of A
         Ordinary Shares or B Ordinary Shares undertakes that it and its
         nominees shall not exercise its rights, pursuant to articles
         2.2(d)(i)(A) and 2.2(d)(i)(C) of the Articles, to convert any A
         Ordinary Shares or B Ordinary Shares beneficially owned by such Offeree
         into Ordinary Shares.

3.       CONDUCT OF BUSINESS

         Pending Completion each Executive shall exercise all rights and powers
         available to it so as to procure that, except with the written consent
         of the Offeror, such consent not to be unreasonably withheld or
         delayed, no Group Company shall:

         (a) incur any expenditure in respect of:

             (i)    any Internal Cost in excess of Pound Sterling20,000 per item
                    or Pound Sterling100,000 in aggregate (other than
                    expenditure expressly specified in the Ribotargets Budget in
                    respect of any Internal Cost); and

             (ii)   any External Cost in excess of Pound Sterling50,000 per
                    item; or

         (b) dispose of or grant any option or right of pre-emption in respect
             of any part of its assets; or

         (c) dispose of or grant any licence in respect of any interest in its
             Intellectual Property Rights other than pursuant to an agreement
             relating to the transfer of materials or a confidentiality
             agreement entered into in the ordinary course of its business; or

         (d) borrow any money; or

         (e) enter into any unusual or abnormal contract or commitment or:

             (i)    grant any lease or third party right in respect of any real
                    estate or transfer or otherwise dispose of any real estate;

                                       25
<PAGE>

             (ii)   make any loan;

             (iii)  enter into any leasing, hire purchase or other agreement or
                    arrangements for payment on deferred terms; or

         (f) declare, make or pay any dividend or other distribution; or

         (g) grant, issue or redeem any mortgage, charge, debenture or other
             security or give any guarantee or indemnity; or

         (h) make any change in the terms and conditions of employment of any of
             its directors or employees or employ or terminate the employment of
             any person save for cause; or

         (i) make, or announce to any person any proposal to make, any change or
             addition to any retirement/death/disability benefit in respect of
             any of its directors or employees or former directors or former
             employees (or any dependant of any such person) or to the Scheme or
             grant or create any additional retirement/death/disability benefit
             or, without limiting the foregoing, take any action or allow any
             action to be taken in relation to the Scheme other than in the
             ordinary course of administering the Scheme or omit to take any
             action reasonably required for the ordinary operation of the
             Scheme; or

         (j) permit any of its insurances to lapse; or

         (k) save as envisaged by this undertaking, create, issue, purchase or
             redeem any class of share or loan capital, or grant any option or
             right to subscribe any share or loan capital other than pursuant to
             the Contribution Deed; or

         (l) save as required by this undertaking, pass any resolution of its
             shareholders or any class of shareholders, whether in general
             meeting or otherwise other than pursuant to the Contribution Deed;
             or

         (m) agree, conditionally or unconditionally, to do any of the
             foregoing; or

         (n) in any other way depart from the ordinary course of its day-to-day
             trading.

                  Each Offeree shall not give any instruction to the Executives
         or to the Group Companies to effect any of the matters referred to in
         this paragraph 3 and shall, on the written request of the Offeror,
         assist (in so far as it is lawfully able) the Executives and the Group
         Companies in complying with their obligations in this paragraph 3.

4.       QUALIFICATIONS

         Paragraph 3 of this schedule shall not operate so as to restrict or
         prevent:

         (a) any matter reasonably undertaken in response to events beyond the
             control of any Offeree or any Group Company, with the intention of
             minimising any adverse effect of such events provided that an
             Executive will inform the Offeror of such matters as soon as
             reasonably practicable;

         (b) completion or performance of any obligations undertaken pursuant to
             any contract or arrangement entered into and disclosed to the
             Offeror prior to the date of this undertaking;

                                       26
<PAGE>

         (c) any other matter undertaken at the written request of the Offeror;
             or

         (d) any action or omission which any member of the Group is required to
             take or omit to take by any applicable law or regulation.

5.       NOTICE OF ANY CHANGE

5.1      Each Offeree shall immediately notify the Offeror in writing of any
         matter or thing which arises or becomes known to it before Completion
         which:

         (a) constitutes (or would after the lapse of time constitute) a breach
             of its Warranties or the undertakings or other obligations on its
             part under this undertaking; or

         (b) indicates that any statement in Part VIII the Circular and Listing
             Particulars relating to it is or might be untrue or misleading.

5.2      Each Executive shall immediately notify the Offeror in writing of any
         matter or thing which arises or becomes known to him before Completion
         which:

         (a) constitutes (or would after the lapse of time constitute) a breach
             of, in the case of Mr Sturge only, his Warranties or, in the case
             of the Executives, the undertakings or other obligations on his
             part under this undertaking; or

         (b) indicates that any statement in the Circular and Listing
             Particulars relating to the Group Companies is or might be untrue
             or misleading; or

         (c) is or might be material in the context of any assumption or other
             matter relevant to any forecast or statement about the Group
             Companies in the Circular and Listing Particulars.

5.3      Each Offeree and Executive shall take all reasonable steps promptly to
         provide the Offeror with any further information which the Offeror
         reasonably requests of it if:

         (a) the Offeror is notified or otherwise becomes aware of anything such
             as is referred to in the above provision of this paragraph 5; or

         (b) the Offeror becomes aware of a significant change or new matter
             which may require the Offeror to prepare supplementary listing
             particulars.


                                       27
<PAGE>

                                   SCHEDULE 7

                          BRITISH BIOTECH BALANCE SHEET




<TABLE>

<S>                                                     <C>           <C>            <C>
1   FIXED ASSETS                                                                       O

    CURRENT ASSETS

2            Interest receivable                            O

3            Tax receivable                                 O

4            Other debtors                                  O

5            Cash & short terms investments                 O            O

    CURRENT LIABILITIES

6            Trade creditors                                O

7            Accruals & other creditors                     O

8            Lease creditors                                O

9            Mortgage                                       O

10           Tax and social security                        O

11           Offer costs                                    O

12           Deferred income                                O           (o)

13  LONG TERM LIABILITIES                                               (o)

14  NET WORKING CAPITAL                                                                O

15  NET ASSETS                                                                         O
</TABLE>


                                       28
<PAGE>

                                   SCHEDULE 8

                            RIBOTARGETS BALANCE SHEET




<TABLE>

<S>                                                     <C>           <C>            <C>
1   FIXED ASSETS                                                                       O

    CURRENT ASSETS

2         Other debtors                                     O

3         Corporation tax receivable                        O

4         Prepayments and accrued income                    O

5         Cash & short terms investments                    O            O

    CURRENT LIABILITIES

6         Trade creditors                                   O

7         Finance lease and hire purchase obligations       O

8         Taxation and social security                      O

9         Other creditors                                   O

10        Accruals and deferred income                      O

11        Offer costs                                       O           (o)

12  LONG TERM LIABILITIES                                               (o)

13  NET WORKING CAPITAL                                                                O

14  NET ASSETS                                                                         O
</TABLE>



                                       29
<PAGE>


                                   SCHEDULE 9

                                 INTERPRETATION

1.       In this undertaking:

         AGREED FORM means, in relation to any document, the form of that
         document which has been initialled for the purpose of identification by
         or on behalf of the Company's Solicitors and the Offeror's Solicitors;

         APAX SHARES means an additional 500 A Ordinary Shares beneficially
         owned by Apax Europe V-A, L.P.;

         A ORDINARY SHARES means the A ordinary shares of Pound Sterling0.10
         each in the capital of the Company;

         ARTICLES means the articles of association of the Company as at the
         date of this undertaking;

         B ORDINARY SHARES means the B ordinary shares of Pound Sterling0.10
         each in the capital of the Company and B ORDINARY SHAREHOLDER means a
         holder of any of them;

         BRITISH BIOTECH BALANCE SHEET means the consolidated balance sheet of
         the Offeror's Group as at 31st March, 2003 prepared in the form and
         including the items shown in the schedule headed "British Biotech
         Balance Sheet", including, without limitation, full accruals for all
         costs incurred in connection with the Offer, and prepared in accordance
         with the accounting policies, principles, practices, evaluation rules
         and procedures, methods and bases adopted by the Offeror in the
         preparation of the British Biotech Management Accounts;

         BRITISH BIOTECH MANAGEMENT ACCOUNTS means the unaudited management
         accounts of the Offeror for the period of ten months ended 28th
         February, 2003 in the Agreed Form;

         BRITISH BIOTECH NET WORKING CAPITAL means the net working capital of
         British Biotech as at 31st March, 2003 as indicated on line 14 of the
         British Biotech Balance Sheet;

         BRITISH BIOTECH ORDINARY SHARES means ordinary shares of 5 pence each
         in the capital of the Offeror;

         BUSINESS DAY means a day (other than a Saturday or Sunday) on which
         banks are generally open in London for normal business;

         CIRCULAR AND LISTING PARTICULARS means the document to be dated on or
         about the date of this undertaking comprising the combined circular to
         shareholders of the Offeror and listing particulars of the Offeror in
         connection with the Offer;

         CODE means The City Code on Takeovers and Mergers;

         COMPANY has the meaning given to it in recital (A);

         COMPANY'S SOLICITORS means CMS Cameron McKenna of Mitre House, 160
         Aldersgate Street, London EC1A 4DD (ref: MGD);

                                       30
<PAGE>

         COMPLETION means completion of the acquisition of the Ribotargets
         Shares, in respect of which the Offer has been accepted, by the Offeror
         and the admission to listing and trading of the Consideration Shares;

         COMPULSORY SALE NOTICE means the notice to be issued by the Company (in
         accordance with article 7.5.2 of the Articles) to each Ribotargets
         Shareholder who has not entered into this undertaking, giving the
         details contained in the Selling Notice and requiring the Ribotargets
         Shareholders to sell their holdings of shares in Ribotargets to the
         Offeror on the terms contained in the Selling Notice;

         CONDITIONS means the conditions set out in paragraph 1 of Part A of
         Appendix I to the Offer Document;

         CONFIDENTIALITY AGREEMENT means the confidentiality agreement between
         the Company and the Offeror dated 6th December, 2002;

         CONSIDERATION SHARES means the 33,375,889 British Biotech Ordinary
         Shares to be allotted and issued to the Ribotargets Shareholders or
         their nominees credited as fully paid in accordance with the terms of
         the Offer Document;

         CONTRIBUTION DEED means the contribution and termination deed in the
         Agreed Form entered into among the existing Ribotargets Shareholders
         and the Company on or before the date of this undertaking pursuant to
         which, inter alia, the Relevant Investors will subscribe for further B
         Ordinary Shares at or prior to Completion;

         COVENANT DEED means the deed poll entered into by British Biotech prior
         to the date of this document giving covenants with respect to the
         conduct of British Biotech's business pending Completion;

         DEFAULTING MEMBER means any member of the Company who fails to comply
         with the terms of the Compulsory Sale Notice;

         EMPLOYEE includes a director and any officer of the Company whether or
         not he has entered into or works under (or, where the employment has
         ceased, worked under) a contract of employment;

         ENCUMBRANCE means any mortgage, charge (fixed or floating), pledge,
         lien, option, right to acquire, assignment by way of security, trust
         arrangement for the purpose of providing security or any other security
         interest of any kind, including retention arrangements and any
         agreement to create any of the foregoing;

         ESCROW COMPLETION means the completion in escrow of the acquisition by
         the Offeror of the Ribotargets Shares, in respect of which the Offer
         has been accepted, save for satisfaction of the Escrow Condition, in
         accordance with the clause headed "Completion";

         ESCROW CONDITION means the Condition in paragraph 1(d) of Part A of
         Appendix I to the Offer Document having been satisfied and the Offer
         not having been withdrawn before satisfaction of such Condition;

         EXECUTIVE'S WARRANTIES means each of the statements set out in Part 3
         of the schedule headed "Warranties";

                                       31
<PAGE>

         EXISTING RIBOTARGETS SHARES means the existing Ordinary Shares, A
         Ordinary Shares and B Ordinary Shares set out opposite each Offeree's
         name in columns (B), (C) and (D) of the schedule headed "The Offerees";

         EXTERNAL COST means any category of expenditure other than an Internal
         Cost;

         FORM OF ACCEPTANCE has the meaning given to it in recital (D);

         GROUP COMPANIES means the Company and the Subsidiary and GROUP COMPANY
         means either of them;

         INTELLECTUAL PROPERTY RIGHTS means rights in trade marks, rights in
         designs, patents, copyright, moral rights, database rights, rights in
         know-how and all other intellectual property rights in each case
         whether registered or unregistered, together with applications for the
         grant of any of these rights, and together also with all rights or
         forms of protection having equivalent or similar effect to any of the
         foregoing which may subsist anywhere in the world;

         INTERNAL COST means any category of expenditure which falls (on the
         basis of preparation consistent with Ribotargets's prior financial
         year) to be treated as an internal cost for the purposes of preparing
         the Ribotargets Budget;

         INVESTOR MAJORITY means the holders of at least 65 per cent. by nominal
         value of the B Ordinary Shares and the A Ordinary Shares;

         LETTER TO OPTION HOLDERS means the letter in the Agreed Form to be sent
         to members of the Ribotargets Option Schemes;

         LONG STOP DATE has the meaning given to it in clause 3.4;

         NEW RIBOTARGETS SHARES means the B Ordinary Shares which are subscribed
         by the Relevant Investors at or prior to Completion in accordance with
         the terms of the Contribution Deed and Clause 4.4;

         OFFER has the meaning given to it in recital (D);

         OFFER DOCUMENT has the meaning given to it in recital (D);

         ORDINARY SHARES means the ordinary shares of Pound Sterling0.10 each in
         the capital of the Company;

         OFFEREE'S GROUP means each Offeree and all its subsidiary undertakings
         and parent undertakings (other than the Group Companies) from time to
         time;

         OFFEREES' WARRANTIES means each of the statements set out in Part 1 of
         the schedule headed "Warranties";

         OFFEROR'S GROUP means the Offeror and all its subsidiary undertakings
         (other than the Group Companies) from time to time;

         OFFEROR'S SOLICITORS means Allen & Overy of One New Change, London EC4M
         9QQ;

         PRESS RELEASE means the press release in the Agreed Form announcing the
         execution of this undertaking, the making of the Offer and the
         publication of the Circular and Listing Particulars;

                                       32
<PAGE>

         RELEVANT INVESTORS means the Ribotargets Shareholders named in column
         (1) of schedule 4 to the Contribution Deed;

         RETIREMENT/DEATH/DISABILITY BENEFIT means any pension, lump sum,
         gratuity or other like benefit given or to be given on retirement or on
         death, or in anticipation of retirement, or, in connection with past
         service, after retirement or death, or to be given on or in
         anticipation of or in connection with any change in the nature of the
         service of the employee in question or given or to be given on or in
         connection with the illness, injury or disability of, or suffering of
         any accident by, an employee;

         RIBOTARGETS BALANCE SHEET means the consolidated balance sheet of the
         Group Companies as at 31st March, 2003 prepared in the form and
         including the items shown in the schedule headed "Ribotargets Balance
         Sheet", including, without limitation, full accruals for all costs
         incurred in connection with the Offer, and prepared in accordance with
         the accounting policies, principles, practices, evaluation rules and
         procedures, methods and bases adopted by the Company in the preparation
         of the Ribotargets Management Accounts;

         RIBOTARGETS BUDGET means the 2003 budget for Ribotargets in the Agreed
         Form;

         RIBOTARGETS MANAGEMENT ACCOUNTS means the unaudited management accounts
         of the Company for the period ended 2nd March, 2003 in the Agreed Form;

         RIBOTARGETS NET WORKING CAPITAL means the net working capital of
         Ribotargets as at 31st March, 2003 as indicated on line 13 of the
         Ribotargets Balance Sheet;

         RIBOTARGETS OPTION SCHEMES means the approved share option plan, the
         unapproved share option plan, the savings-related share option scheme
         and the enterprise management incentive scheme operated by the Company;

         RIBOTARGETS SHAREHOLDERS' AGREEMENT means the Subscription and
         Shareholders' Agreement dated 25th September, 2001 among, inter alia,
         the Company, the Medical Research Council, the New Investors (as
         defined therein) and the Existing Investors (as defined therein);

         RIBOTARGETS SHARES means all the existing issued Ordinary Shares, A
         Ordinary Shares or B Ordinary Shares and any further such shares which
         are allotted or issued before the date upon which the Offer becomes
         wholly unconditional (save only as to the Escrow Condition), including
         any New Ribotargets Shares which are issued pursuant to the
         Contribution Deed, and RIBOTARGETS SHAREHOLDER means a holder of any of
         them;

         SCHEME means the Ribotargets Group Personal Pension Scheme;

         SECURITIES ACT means the United States Securities Act of 1933, as
         amended;

         SELLING NOTICE means the notice in the Agreed Form to be issued by the
         Offerees to the Company in accordance with article 7.5.1 of the
         Articles;

         SUBSIDIARY means the company mentioned in the schedule headed "The
         Subsidiary";

         SUBSIDIARY means a subsidiary for the purposes of the Companies Act
         1985;

         SUBSIDIARY UNDERTAKING and PARENT UNDERTAKING have the meanings given
         in section 258 of the Companies Act 1985;

                                       33
<PAGE>

         TERMINATION DEED means the deed in the Agreed Form between the Company
         and the Offeror pursuant to which paragraph 9 of the Confidentiality
         Agreement is terminated;

         UK LISTING AUTHORITY means the Financial Services Authority acting in
         its capacity as the competent authority for the purposes of Part VI of
         the Financial Services and Markets Act 2000;

         UNITED STATES and US PERSON have the meanings given in Rule 902 of
         Regulation S under the Securities Act;

         US OFFEREE means each of Caduceus Private Investment LLP, Orbimed
         Associates LLC, PW Juniper Crossover Fund LLC (each c/o Orbimed
         Advisors, 767 3rd Avenue, New York NY 10017), J.P. Morgan Partners
         (BHCA) Limited (1221 Avenue of the Americas, New York 10020, USA), Apax
         UK V-A, L.P. (1 Portland Place, London W1B 1PT) and Apax Europe V-A,
         L.P. (13-15 Victoria Road, St. Peter Port, Guernsey GY1 32D) (together,
         the US OFFEREES);

         US OFFEREES' WARRANTIES means each of the statements set out in Part 2
         of the schedule headed "Warranties";

         WARRANTIES means the warranties contained in the clause headed
         "Warranties"; and a person shall be deemed to be CONNECTED with another
         if that person is connected with another within the meaning of section
         839 of the Taxes Act 1988.

2.       Any express or implied reference to an enactment (which includes any
         legislation in any jurisdiction) includes references to:

         (a) that enactment as amended, extended or applied by or under any
             other enactment before or after the date of this undertaking;

         (b) any enactment which that enactment re-enacts (with or without
             modification); and

         (c) any subordinate legislation (including regulations) made (before or
             after signature of this undertaking) under that enactment, as
             re-enacted, amended, extended or applied as described in paragraph
             (a) above, or under any enactment referred to in paragraph (b)
             above,

         in each case except to the extent that any such amendment, extension,
         application or re-enactment made after the date of this undertaking
         increases or would increase the liability of all or any of the
         Offerees.

3.       In this undertaking:

         (a) words denoting persons shall include bodies corporate and
             unincorporated associations of persons;


         (b) references to an individual include his estate and personal
             representatives; and

         (c) references to a party to this undertaking include references to the
             successors or assigns (immediate or otherwise) of that party.


                                       34
<PAGE>


                                   SIGNATORIES


Executed by APAX UK V-A, L.P.                   )
acting by its manager                           )    .......................
APAX PARTNERS LTD acting by:                    )    (Director)
                                                )
                                                )    ......................
                                                )    (Director/Secretary)


Executed as a Deed by APAX UK V-B               )    .......................
acting by its manager                           )    (Director)
APAX PARTNERS LTD acting by:                    )
                                                )    .......................
                                                )    (Director/Secretary)


Executed by APAX EUROPE V - A, L.P.             )    .......................
acting by its investment manager                )    (Director)
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )
                                                )    .......................
                                                     (Director/Secretary)


Executed as a Deed by                           )    .......................
APAX EUROPE V - B, L.P.                         )    (Director)
acting by its investment manager                )
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )    .......................
                                                     (Director/Secretary)


Executed as a Deed by                           )    ......................
APAX EUROPE V - C GmbH & CO. KG                 )    (Director)
acting by its investment manager                )
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )    .......................
                                                     (Director/Secretary)



Executed as a Deed by                           )    .......................
APAX EUROPE V - D, L.P.                         )    (Director)
acting by its investment manager                )
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )    .......................
                                                     (Director/Secretary)


                                       35
<PAGE>



Executed as a Deed by                           )    .......................
APAX EUROPE V - E, L.P.                         )    (Director)
acting by its investment manager                )
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )    .......................
                                                     (Director/Secretary)


Executed as a Deed by
APAX EUROPE V - F, C.V.                         )    .......................
acting by its investment manager                )    (Director)
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )
                                                     .......................
                                                     (Director/Secretary)


Executed as a Deed by                           )     .......................
APAX EUROPE V - G, C.V.                         )    (Director)
acting by its investment manager                )
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )    .......................
                                                     (Director/Secretary)


Executed as a Deed by                           )    .......................
APAX EUROPE V - 1, L.P.                         )    (Director)
acting by its investment manager                )
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )    .......................
                                                     (Director/Secretary)


Executed as a Deed by                           )    .......................
APAX EUROPE V-2, L.P.                           )    (Director)
acting by its investment manager                )
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )    .......................
                                                     (Director/Secretary)


Executed as a Deed by                           )    .......................
AP V GmbH & CO. KG                              )    (Director)
acting by its attorney                          )
APAX PARTNERS EUROPE MANAGERS                   )
LTD acting by:                                  )    .......................
                                                     (Director/Secretary)


Executed as a Deed by                           )
3i GROUP PLC acting by its attorney             )
in the presence of:                             )


                                       36
<PAGE>


Executed as a Deed on behalf of                 )
3i BIOSCIENCE INVESTMENT TRUST PLC              )
acting by its manager                           )
3i INVESTMENTS PLC                              )
acting by                                       )
                                                )
as attorney for                                 )
3i INVESTMENTS PLC                              )
in the presence of:                             )
                                                )


Executed as a Deed by ADVENT VCT PLC            )
acting by                                       )    .....................
                                                )     (Director)
and                                             )
                                                )
for and on behalf of                            )    .......................
ADVENT VCT PLC                                  )    (Director/Secretary)


Executed as a Deed by ADVENT VENTURE PARTNERS   )
acting by                                       )    .......................
                                                )    (Director)
and                                             )
                                                )
for and on behalf of                            )    .......................
ADVENT VENTURE PARTNERS acting as manager       )    (Director/Secretary)
of ADVENT PRIVATE EQUITY FUND III 'A'           )


Executed as a Deed by ADVENT VENTURE PARTNERS   )
acting by                                       )    .......................
                                                )     (Director)
and                                             )
                                                )
for and on behalf of                            )    .......................
ADVENT VENTURE PARTNERS acting as manager       )    (Director/Secretary)
of ADVENT PRIVATE EQUITY FUND III 'B'           )


Executed as a Deed by ADVENT VENTURE PARTNERS   )
acting by                                       )    .......................
                                                )    (Director)
and                                             )
                                                )
for and on behalf of                            )    .......................
ADVENT VENTURE PARTNERS acting as manager       )    (Director/Secretary)
of ADVENT PRIVATE EQUITY FUND III 'C'           )


                                       37

<PAGE>


Executed as a Deed by ADVENT VENTURE PARTNERS   )
acting by                                       )    .......................
                                                )     (Director)
and                                             )
                                                )
for and on behalf of                            )    .......................
ADVENT VENTURE PARTNERS acting as manager       )    (Director/Secretary)
of ADVENT PRIVATE EQUITY FUND III 'D'           )


Executed as a Deed by ADVENT VENTURE PARTNERS   )
acting by                                       )    .......................
                                                )    (Director)
and                                             )
                                                )
for and on behalf of                            )    .......................
ADVENT VENTURE PARTNERS as manager              )    (Director/Secretary)
of ADVENT PRIVATE EQUITY FUND III               )
GMBH & CO. KG                                   )
in the presence of:                             )
                                                )


Executed as a Deed by ADVENT VENTURE PARTNERS   )
acting by                                       )    .......................
                                                )     (Director)
and                                             )
                                                )
for and on behalf of                            )    .......................
ADVENT VENTURE PARTNERS as manager of           )    (Director/Secretary)
ADVENT MANAGEMENT III LIMITED                   )
PARTNERSHIP                                     )
in the presence of :                            )
                                                )


Executed as a Deed by ADVENT VENTURE PARTNERS   )
acting by                                       )    .......................
                                                )     (Director)
and                                             )
                                                )
for and on behalf of                            )    .......................
ADVENT VENTURE PARTNERS as manager of           )    (Director/Secretary)
ADVENT PRIVATE EQUITY FUND III                  )
AFFILIATES                                      )
in the presence of :                            )
                                                )


                                       38

<PAGE>


Executed as a Deed by QUESTER VCT 2 PLC         )    .......................
acting by                                       )    (Director)
                                                )
and                                             )
                                                )
for and on behalf of                            )    .......................
QUESTER VCT 2 PLC                               )    (Director/Secretary)


Executed as a Deed by QUESTER VCT 3 PLC         )    .......................
acting by                                       )    (Director)
                                                )
and                                             )
                                                )    .......................
for and on behalf of                            )    (Director/Secretary)
QUESTER VCT 3 PLC                               )


Executed as a Deed by                           )
J.P. MORGAN PARTNERS (BHCA), L.P.               )
acting by JPMP MASTER FUND MANAGER, L.P.        )
its General Partner,                            )
by JPMP CAPITAL CORP.,                          )
its General Partner,                            )
by                                              )
Name:                                           )
Title:                                          )
in the presence of:                             )


Executed as a Deed by                           )
                                                )
and                                             )
                                                )
for and on behalf of                            )
THE MEDICAL RESEARCH COUNCIL                    )


Executed as a Deed by ALPINVEST HOLDING NV      )
acting by its sole Managing Director            )
NIB CAPITAL PRIVATE EQUITY NV                   )
and                                             )
                                                )
acting under the authority of                   )
the Company                                     )
ALPINVEST HOLDING NV                            )


                                       39

<PAGE>


Executed as a Deed by ORBIMED CAPITAL LLC       )
acting by                                       )
                                                )
and                                             )
                                                )
for and on behalf of                            )
CADUCEUS PRIVATE INVESTMENTS, LP                )
acting by ORBIMED CAPITAL LLC,                  )
as its general partner                          )


Executed as a Deed by ORBIMED ADVISORS, LLC     )
acting by                                       )
                                                )
and                                             )
                                                )
for and on behalf of                            )
ORBIMED ASSOCIATES LLC                          )
acting by its managing member                   )
ORBIMED ADVISORS, LLC                           )


Executed as a Deed by ORBIMED ADVISORS INC.     )
acting by                                       )
                                                )
and                                             )
                                                )
for and on behalf of                            )
PW JUNIPER CROSSOVER FUND, L.L.C.,              )
acting by                                       )
its managing member PW JUNIPER CROSSOVER        )
MANAGEMENT, L.L.C.                              )
acting by its managing member                   )
ORBIMED ADVISORS INC.                           )


Executed as a Deed by RENDEX N.V.               )
acting by                                       )
                                                )
and                                             )
                                                )
acting under the authority                      )
of that Company                                 )
RENDEX N.V.                                     )


Executed as a Deed by                           )
SIMON STURGE                                    )
in the presence of:                             )


Executed as a Deed by                           )
SUSAN LOWTHER                                   )
in the presence of:                             )



                                       40
<PAGE>

Executed as a Deed by                           )
ALAN DRIVER                                     )
in the presence of:                             )


Executed as a Deed by                           )
PROFESSOR COLIN S. GOODCHILD                    )
in the presence of:                             )


Executed as a Deed by                           )
DR RAY NADESON                                  )
in the presence of:                             )


Executed as a Deed by MONASH COMMERCIAL         )    .......................
PROPRIETARY LIMITED acting by                   )    (Director)
                                                )
and                                             )
                                                )
for and on behalf of                            )    .......................
MONASH COMMERCIAL PROPRIETARY                   )
LIMITED                                         )    (Director/Secretary)



Executed as a Deed by BIOCOMM SERVICES          )    .......................
PROPRIETARY LIMITED acting by                   )    (Director)
                                                )
and                                             )
                                                )
for and on behalf of                            )    .......................
BIOCOMM SERVICES PROPRIETARY LIMITED            )    (Director/Secretary)


Executed as a Deed by                           )    .......................
BRITISH BIOTECH PLC                             )    (Director)
acting by                                       )
and                                             )
                                                )    .......................
                                                     (Director/Secretary)



                                       41