<PAGE>
                                                                    EXHIBIT 4.12

         (1)      CAMBRIDGE ANTIBODY TECHNOLOGY GROUP plc or CAMBRIDGE
                  ANTIBODY TECHNOLOGY LIMITED/1/

         (2)      [Executive]


                               SERVICE AGREEMENT

/1/ The Service Contracts of the Chief Executive Officer and the Finance
Director are with Cambridge Antibody Technology Group plc. The Service Contracts
of the Chief Technology Officer and the Medical Director are with CAT Limited.
<PAGE>

<TABLE>
<CAPTION>
                                   CONTENTS

Clause    Subject                                                           Page
<S>       <C>                                                               <C>

1.        Definitions and Interpretation                                    3

2.        Appointment                                                       3

3.        Duties                                                            4

4.        Outside Activities                                                5

5.        Remuneration                                                      5

6.        Expenses                                                          6

7.        Car                                                               6

8.        Holidays                                                          6

9.        Confidentiality                                                   7

10.       Inventions                                                        7

11.       Termination and sickness                                          8

12.       Obligations on termination                                        9

13.       Obligations after termination                                     10

14.       Amalgamation or Reconstruction                                    10

15.       Notices                                                           10

16.       Previous Contracts                                                11

17.       Governing Law                                                     11

18.       Statement of terms of employment                                  11
</TABLE>

                                       2
<PAGE>

<TABLE>
<S>       <C>                                                               <C>
19.       Waiver                                                            11

20.       Appendix                                                          12
</TABLE>

                                       3
<PAGE>

Dated:   10 February 1997


BETWEEN:

(1)               CAMBRIDGE ANTIBODY TECHNOLOGY GROUP plc/CAT Limited;

and

(2)               [EXECUTIVE]


1.     DEFINITIONS AND INTERPRETATION

1.1    In this Agreement the following words shall have the following meanings:-

       "Board"                    :    the board of directors of the Company;

       "Chairman"                 :    the Chairman of the board of directors;

       "Company"                  :    Cambridge Antibody Technology Group plc,
                                       a company incorporated under the laws of
                                       England and Wales with registered number
                                       3234033;

       "Executive"                :    [_________];

       "Group"                    :    the Company and any other company which
                                       from time to time is its Subsidiary or
                                       Holding Company or in which the Company
                                       controls not less than 25 per cent of the
                                       voting shares;

       "Holding Company"          :    has the same meaning as given to it in
                                       Section 736 of the Companies Act 1985;

       "Remuneration Committee"   :    the Remuneration Committee of the Board;

       "Subsidiary"               :    has the same meaning as given to it in
                                       Section 736 of the Companies Act 1985.

1.2    The headings in this Agreement are for convenience only and are not to be
       used as an aid to construction of this Agreement.

                                       4
<PAGE>

1.3    References to provisions of statutes, rules or regulations shall be
       deemed to include references to such provisions as amended, modified or
       re-enacted from time to time.

2.     APPOINTMENT

2.1    The Company shall engage the Executive and the Executive shall serve the
       Company as its [___________] or in such other comparable capacity as the
       Company may from time to time reasonably require, it being understood
       that this will not result in any reduction in the status of the
       Executive. The Executive shall also join the Board.

2.2    The employment of the Executive commenced on [_________] and shall
       continue until terminated as provided in this Agreement.

3.     DUTIES

3.1    The Executive shall:

       3.1.1    except during holidays (Clause 8 of this agreement),
                unavoidable absence due to sickness, or other imperative
                cause, or when performing duties under any non-executive
                directorship approved by the Board under Clause 4 of this
                agreement, devote the whole of his time and attention and
                abilities during normal business hours and at such other times
                as the Company or his duties may reasonably require to the
                business of the Company and undertake such duties and exercise
                such powers and authorities in relation to the Company and the
                business of the Company as the [Chief Executive
                Officer/Board]2 shall from time to time assign to or vest in
                the Executive;

       3.1.2    in the discharge of such duties and in the exercise of such
                powers conform to, observe and comply with all resolutions and
                directions from time to time made or given by the [Chief
                Executive Officer/Board];

       3.1.3    report directly to the [Chief Executive Officer/Board] in such
                a manner and so often as the [Chief Executive Officer/Board]
                may from time to time require;

       3.1.4    faithfully and diligently serve the Company and use his best
                endeavours to maintain, extend, develop and promote its
                interests;

       3.1.5    use his best endeavours to promote the interests and the welfare
                of the Company and to develop and maintain the business of the
                Company;

       3.1.6    not engage in any activity which will detract from the proper
                performance of his duties;

________
/2/ If the Service Contract is with the Chief Executive Officer, then the Board
is used, otherwise, the Chief Executive Officer is used.

                                       5
<PAGE>

       3.1.7    at all times perform his duties with proper skill and care.

3.2    The Executive may be required in pursuance of his duties hereunder:

       3.2.1    to perform services not only for the Company but also for any
                other company in the Group and without further remuneration
                (except as otherwise approved by the Remuneration Committee and
                agreed in writing) to accept such offices in other companies in
                the Group as the Company may from time to time reasonably
                require and if such offices carry any fee or other remuneration
                the Executive will immediately pay or direct payment of it to
                the Company;

       3.2.2    to work at such places within the United Kingdom as the Company
                may require; and

       3.2.3    to travel to such places whether in or outside the United
                Kingdom by such means and on such occasions as the Company may
                from time to time reasonably require, such travel to be in
                accordance with the terms of the Company's travel policy for the
                time being.

3.3    Any duties undertaken by the Executive as a director of the Company or
       any other Company in the Group are subject to the Articles of Association
       of the relevant company for the time being.

3.4    The Company may at any time after serving or receiving notice to
       terminate this Agreement suspend the Executive from the performance of
       his duties and/or exclude him from any premises of the Company or any
       company in the Group and/or appoint a replacement to perform some or all
       of his duties instead of him and/or require him to resign as a director
       of the Company and from any office or appointment held under clause 3.2.1
       but salary and other contractual benefits will not cease to be payable or
       provided by reason only of that suspension and/or exclusion. This clause
       shall not affect the general right of the Company to suspend the
       Executive for a limited period not to exceed 20 consecutive working days
       for the purposes of conducting a disciplinary hearing and/or
       investigation.

4.     OUTSIDE ACTIVITIES

       Except as a representative of the Company or with the previous written
       approval of the Chairman the Executive shall not during his full-time
       employment by the Company be directly or indirectly employed, engaged,
       concerned or interested in any capacity in any other trade or business
       (whether paid or unpaid) save as a holder of the legal or equitable
       interest (as defined by Schedule 13 of the Companies Act 1985) in the
       shares or securities of a company any of whose shares or securities are
       quoted or dealt in on any recognised Stock Exchange provided that any
       such holding shall not exceed three per cent (3%) of the whole or any
       class of the issued share capital of the company concerned.

                                       6
<PAGE>

       The Board will consider any reasonable request from the Executive to
       serve as a non-executive director on the board(s) or other companies.

5.     REMUNERATION

5.1    The Company shall pay to the Executive by way of remuneration for his
       services (less deductions for tax and national insurance contributions) a
       basic salary of [_____] pounds sterling per annum/3/ to be paid by equal
       monthly instalments in arrears on the last working day of each month.

5.2    The quantum of the remuneration of the Executive will be reviewed
       annually by the Remuneration Committee with effect for the first time
       from 1 October 1997.

5.3    Subject to the Executive satisfying the medical criteria of the insurer
       and provided that cover is available at a reasonable premium (as
       determined by the Remuneration Committee) for an individual of the
       Executive's age, the Company will insure the life of the Executive from
       year to year during the term of his employment under and on the terms of
       the Company's Personal Accident Scheme (described in the Company's
       Employee Benefits Handbook) or any successor scheme. The Company will
       also provide disability cover under and on the terms of its Income
       Protection Scheme (described in the Company's Employee Benefits
       Handbook).

5.4    The Company will contribute ten per cent (10%) of the Executive's basic
       salary applicable at the time to the Company's Group Personal Pension
       Scheme. If at any time legislation or regulation limits or prohibits such
       contribution, the Company will contribute up to the amount permitted and
       will make available any surplus of the said ten per cent (10%) to the
       Executive for investment in a pension fund agreed between the Company and
       the Executive, provided that the total cost to the Company under this
       clause 5.4 shall not in any circumstances exceed ten per cent (10%) of
       the Executive's basic salary.

5.5    The Executive shall not, except with the prior approval of the
       Remuneration Committee, accept any bonus, commission, contract, award,
       gift in money or in kind from any person in excess of (pound)100 for any
       single gift and (pound)250 in aggregate in any calendar year, except the
       Company, as an inducement or reward for any act or forbearance or in
       connection with any matter of business transacted by or on behalf of the
       Company.

5.6    The Company shall contribute up to one thousand five hundred pounds
       ((Pounds)1,500) per annum towards the cost of providing private medical
       insurance cover, approved by the Company, for the benefit of the
       Executive and his immediate family.

6.     EXPENSES

_____________
/3/ The salary for each of the directors is disclosed in the text of the
registration statement.

                                       7
<PAGE>

6.1    The Executive shall be entitled to be repaid all travelling, hotel and
       other expenses reasonably and properly incurred by him in the performance
       of his duties under this Agreement, subject to the production to the
       Company of supporting vouchers and documents.

6.2    The Executive shall use any credit card or similar facility provided to
       him by the Company solely for payment of expenses reasonably and properly
       incurred by him in the performance of his duties under this Agreement.

6.3    The Company shall reimburse to the Executive all of the rental and call
       charges of a facsimile at his home and the costs of installing and
       operating a business telephone line at his home for the performance of
       his duties.

6.4    The Company shall reimburse the Executive his membership fees for agreed
       professional societies and agreed professional subscriptions.

6.5    The Company shall reimburse the Executive for reasonable legal fees,
       estate agents' commission, advertising costs, mortgage redemption costs
       and removal charges incurred by the Executive in relocating himself and
       his family to the vicinity of the Company's premises if such a move takes
       place within two (2) years of his joining the Company.

7.     CAR

7.1    The Company shall pay to the Executive a non-pensionable allowance at
       such rate as the Remuneration Committee may from time to time determine
       in lieu of the provision to him of a company car. The Executive agrees
       that he shall procure the availability at all times of a car which is
       suitable (in terms of age, make, specification and model) for use by him
       on Company business, that he will ensure that the car is properly
       insured, maintained and repaired for such use and will forthwith report
       to the Company any accidents in which he is involved on Company business.
       The Company will reimburse the Executive for any business mileage at the
       rate approved by the Inland Revenue for such car.

8.     HOLIDAYS

8.1    The Executive shall be entitled to twenty five (25) working days' holiday
       (in addition to public holidays) in each holiday year at full salary to
       be taken at such time or times as may be approved by the [Chief Executive
       Officer/Chairman]. The Company's holiday year commences 1 January.
       Holidays not taken (up to a maximum of ten (10) days of the holiday
       entitlement) may be carried over to the subsequent year. Holiday
       entitlement during the first year in which the Executive shall have
       joined shall be on a pro-rata basis.

8.2    Upon termination of the Executive's engagement hereunder (otherwise
       than in pursuance of clause 11.1 or clause 11.2) his entitlement to
       holiday will be calculated on the basis of one twelfth (1/12) of his
       annual holiday entitlement for each completed calendar month of service

                                       8
<PAGE>

       in the then current holiday year and payment in lieu will be made for
       any whole day's holiday not taken at the date of such determination.
       The number of days resulting from this calculation will be multiplied
       by one two hundred and sixtieth (1/260) of the Executive's annual
       salary.

                                       9
<PAGE>

9.       CONFIDENTIALITY

9.1      The Executive shall not make use of, divulge or communicate to any
         person (save in the proper performance of his duties under this
         Agreement) any of the trade secrets or other confidential information
         of or relating to the Company or any other company in the Group which
         he may have received or obtained while in the service of the Company or
         any other company in the Group. This restriction shall continue to
         apply after the termination of the employment of the Executive without
         limit in point of time.

9.2      For the purposes of clause 9, confidential information shall include,
         but shall not be limited to:

         9.2.1    information relating to any reagents, chemical compounds or
                  biological material being used or developed by the Company or
                  any other company in the Group;

         9.2.2    all technical, biotechnical, biological or biochemical
                  information relating to the research or work being carried out
                  by the Company or any other company in the Group;

         9.2.3    inventions relating to past, existing and future research
                  and/or products;

         9.2.4    lists of customers and suppliers and details of contracts with
                  customers and suppliers of the Company or any company in the
                  Group; and

         9.2.5    information supplied to the Company or any company in the
                  Group or to the Executive in confidence by customers.

9.3      The undertakings in this clause 9 shall not apply to:

         9.3.1    information that at the time it is received or obtained by the
                  Executive is published or otherwise generally available to the
                  public;

         9.3.2    information which after it is received or obtained by the
                  Executive is published or otherwise becomes generally
                  available to the public, otherwise than through any wrongful
                  act or omission on the part of the Executive;

         9.3.3    information rightly acquired from a third party who did not
                  obtain it under a pledge of secrecy to the Company or any
                  other company in the Group;

         9.3.4    information ordered to be disclosed by a court of competent
                  jurisdiction or other wise required by law to be disclosed.

9.4      The obligations of the Executive under this clause 9 shall be in
         addition to and not in substitution for any implied obligations imposed
         upon him by law in relation to the use or disclosure of confidential
         information.

                                       10
<PAGE>

10.      INVENTIONS

10.1     in this clause 10 the words "Intellectual Property" shall include
         patents, trade marks (whether registered or unregistered), registered
         or unregistered design, utility models, copyrights (including design
         copyrights), applications for any of the foregoing and the right to
         apply for them in any part of the world, discoveries, creations,
         inventions (or improvements upon or additions to an invention),
         confidential information, know-how and any research effort relating to
         any of the foregoing, business names (whether registrable or not),
         moral rights and any similar rights in any country.

10.2     If the Executive makes, discovers or creates Intellectual Property in
         the course of his duties under this Agreement the parties agree that,
         in this respect, the Executive has a special obligation to further the
         interests of the Company.

10.3     Subject to the provisions of the Patents Act 1977 and the Copyright,
         Designs and Patents Act 1988, if at any time during his employment
         under this Agreement the Executive makes, creates or discovers or
         participates in the making, creation or discovery of any Intellectual
         Property relating to or capable of being used in the business of the
         Company or in the business of any other company within the Group, he
         shall immediately communicate full details of such Intellectual
         Property to the Company and such Intellectual Property shall be the
         absolute property of the Company. At the request and expense of the
         Company, the Executive shall give and supply all such information,
         data, drawings and assistance as may be requisite to enable the Company
         to exploit such Intellectual Property to the best advantage and shall
         execute all documents and do all acts and things which may be necessary
         or desirable for obtaining patent or other protection for such
         Intellectual Property in such parts of the world as may be specified by
         the Company and for vesting the same in the Company or as it may
         direct. The Executive hereby irrevocably waives all moral rights
         related to the works covered by this Clause 10.3, the copyright of
         which belongs to the Company.

10.4     The Executive irrevocably appoints the Company to be his attorney in
         his name and on his behalf to sign, execute or do any such instrument
         or thing and generally to use his name for the purpose of giving the
         Company (or its nominee) the full benefit of the provisions of this
         clause and, in favour of any third party, a certificate in writing
         signed by any director or the Company Secretary that any instrument or
         act falls within the authority conferred by this clause shall be
         conclusive evidence that such is the case.

11.      TERMINATION AND SICKNESS

11.1     This Agreement may be terminated immediately by the Company by notice
         in writing if the Executive shall:

                                       11
<PAGE>

         11.1.1   have committed any breach and after warning in writing either
                  repeated or continued that breach of his obligations
                  hereunder; or

         11.1.2   be involved in any act, matter or thing or engage in any
                  conduct which in the reasonable opinion of the [Chief
                  Executive Officer/Board] might bring the Executive or the
                  Company or any company in the Group into disrepute or might be
                  detrimental to the Company or any company in the Group or
                  their businesses; or

         11.1.3   voluntarily resign as a director of the Company without good
                  cause after having been appointed to that office; or

         11.1.4   be guilty of dishonesty whether or not in connection with or
                  referable to his employment under this Agreement; or

         11.1.5   be convicted of any criminal offence (excluding an offence
                  under road traffic legislation, for which the Executive is not
                  sentenced to any term of imprisonment, whether suspended or
                  not); or

         11.1.6   become of unsound mind or a patient under the Mental Health
                  Act 1983; or

         11.1.7   become unable to pay his debts as they fall due, make any
                  compensation or arrangement with his creditors or become
                  bankrupt; or

         11.1.8   have been disqualified from being a director under the Company
                  Directors Disqualification Act 1986.

11.2     If the Executive shall during the continuance of this Agreement be
         incapacitated by ill-health or accident from performing his duties
         hereunder (and he shall if required produce to the Company evidence of
         such incapacity) for a period or periods aggregating ninety (90)
         working days or more in any period of twelve (12) months the Company
         may by written notice to the Executive forthwith or as from a future
         date specified in the notice discontinue payment in whole or in part of
         his remuneration and other benefits under clause 5 hereof until such
         incapacity shall cease or (whether or not his remuneration and benefits
         shall have been discontinued as aforesaid) terminate this Agreement by
         giving such notice as the Executive is then entitled to receive under
         Section 86 of the Employment Rights Act 1996. Otherwise the
         remuneration and benefits shall continue to be payable to the Executive
         under clause 5 notwithstanding such incapacity but the Company shall be
         entitled to set off or deduct therefrom the amount of any statutory
         sick pay and/or sickness related benefit to which the Executive is
         entitled under Social Security legislation for the time being in force.

         The Company shall not have any liability to pay any benefit to the
         Executive under any scheme unless it receives payment of the benefit
         from the insurers of the benefits under the scheme.

                                       12
<PAGE>

11.3     Either party may terminate this Agreement by giving not less than
         twelve (12) months notice in writing to that effect expiring at any
         time.

11.4     The Company shall be entitled to pay salary in its absolute discretion
         in lieu of notice or of an unexpired period of notice. For the
         avoidance of doubt, this right shall apply where the notice is given by
         the Company or the Executive. Any payment in lieu of notice shall
         consist of a sum equivalent to the Executive's basic salary (at the
         rate applicable at the date notice is given) and including any benefits
         enjoyed by the Executive at that time, for the notice period or any
         unexpired period of notice and shall be subject to such deductions for
         tax and national insurance as the Company is required to make.

11.5     The Agreement shall automatically terminate when the Executive reaches
         the age of sixty-five (65).


12.      OBLIGATIONS ON TERMINATION

         Upon the giving of notice pursuant to clause 11.2 above or termination
         of this Agreement for any other reason the Executive shall:

12.1     forthwith or within seven days of a request from the Company resign
         from office as a director of the Company and all offices held by him in
         any other companies in the Group and his membership of any organisation
         acquired by virtue of his tenure of any such office, and should he fail
         to do so he hereby irrevocably authorises the Company Secretary for the
         time being in his name and on his behalf to sign any documents and do
         anything necessary or requisite to give effect thereto; and

12.2     deliver to the Company's premises during normal business hours all
         property in his possession or under his control belonging to the
         Company or any other company in the Group including but not limited to
         keys, security and computer passes, computer hardware, facsimile
         machines and all documents and other records (whether on paper,
         magnetic tape or in any other form and including correspondence, lists
         of clients or customers, notes, memoranda, software, plans, drawings
         and other documents and records of whatsoever nature and all copies
         thereof) made or compiled or acquired by the Executive during his
         employment hereunder and concerning the business, finances or affairs
         of the Company or any other company in the Group or its clients or
         customers; and

12.3     execute forthwith stock transfer forms in favour of the Company or any
         other company in the Group or such nominee as they shall appoint in
         respect of any nominee shares held by the Executive on behalf of the
         Company or any company in the Group.

13.      OBLIGATIONS AFTER TERMINATION

                                       13
<PAGE>

13.1     The Executive shall not, so as to compete with the Company or any
         company in the Group and/or to harm the goodwill of the Company or any
         company in the Group, during the twelve (12) months after the
         termination of this Agreement, directly or indirectly, canvass or
         solicit business from or do business with any customer or supplier of
         the Company or any company in the Group or any other person with whom
         the Executive shall have had material dealings in the course of his
         duties hereunder in the twelve months (12) immediately preceding the
         termination of this Agreement.

13.2     The Executive shall not, during the twelve (12) months after the
         termination of this Agreement, directly or indirectly induce or seek to
         induce any employee of the Company or any company in the Group, who was
         such an employee at the termination of this Agreement employed in an
         Executive, Vice Presidential, Managerial or Senior Scientist
         positionand with whom the Executive shall have had material dealings in
         the course of his duties hereunder in the twelve (12) months
         immediately preceding the termination of this Agreement, to leave his
         or her employment, whether or not this would be a breach of contract on
         the part of the employee.

13.3     The Executive shall not, during the six (6) months after the
         termination of this Agreement, carry on or be interested in business in
         competition with the Company or any company in the Group, whether as
         principal, agent, director, partner, proprietor, employee or otherwise.

13.4     Each of the restrictions contained in this clause 13 are considered
         reasonable by the Company and the Executive and are intended to be
         separate and severable. In the event that any of the restrictions shall
         be held void, but would be valid if part of the wording thereof were
         deleted, such restriction shall apply with such deletion as may be
         necessary to make it valid and effective.


14.      AMALGAMATION OR RECONSTRUCTION

         If at any time the Executive's employment is terminated in connection
         with any reconstruction or amalgamation of the Company or its
         subsidiaries (whether by winding up or otherwise) and the Executive
         receives an offer on terms no less favourable to him overall than the
         terms of this Agreement from any company involved in such
         reconstruction or amalgamation, the Executive shall have no claim
         whatsoever against the Company or any such subsidiary arising out of
         such termination if he shall have refused to accept such offer of
         employment. The provisions of this clause are without prejudice to the
         operation, statute or statutory regulations in appropriate cases.


15.      NOTICES

         Any notice to be given under this Agreement shall be given in writing
         and may be sent addressed in the case of the Company to its registered
         office or principal place of business for the time being and in the
         case of the Executive to him at his last known place of residence or

                                       14
<PAGE>

         given personally and any notice given by post shall be deemed to have
         been served at the expiration of forty-eight (48) hours after the same
         was posted. Notice may also be given by facsimile in which case it
         shall be deemed to have been served twelve (12) hours after the same
         was transmitted.

16.      PREVIOUS CONTRACTS

         This Agreement is in substitution for any previous contract of service
         or for services between the Company or any company in the Group and the
         Executive which shall be deemed to have been terminated by mutual
         consent as from the commencement of his engagement hereunder.


17.      GOVERNING LAW

         This Agreement shall be governed by and construed in accordance with
         English law.


18.      STATEMENT OF TERMS OF EMPLOYMENT

         The information in this Agreement and Appendix hereto constitutes a
         written statement of the terms of employment of the Executive in
         compliance with the provisions of Section 2 of the Employment Rights
         Act 1996.

19.      WAIVER

         The waiver of any right the Company may have by virtue of this
         Agreement shall not constitute a continuing or repeated waiver or of
         any other right.



EXECUTED AS A DEED
BY THE COMPANY
ACTING BY:-                         ..........................
                                    Director

                                    ..........................
                                    Secretary

EXECUTED AS A DEED
BY THE EXECUTIVE:-                  ..........................



                                       15
<PAGE>

                                    Signed


                                    ..........................
                                    Name





WITNESSED BY:-                      ..........................
                                    Signed


                                    Name:


                                    Address:

                                       16
<PAGE>

                                   APPENDIX

(1)    Date of Commencement of Period of Continuous Employment - The Executive
       has been in the employment of the Company (including reckonable service
       with its subsidiary or associated companies) since [___________].

(2)    Rate of Remuneration and the intervals at which it is paid is specified
       in clause 5.

(3)    There are no specific terms and conditions relating to hours of work
       except as provided in clause 3.1.

(4)    The terms and conditions relating to holidays are contained in clause 8
       and those relating to sickness are contained in clause 11.2.

(5)    The Company operates a pension scheme which the Executive is entitled to
       join - clause 5.6. A contracting-out certificate is not in force in
       respect of the Executive's employment.

(6)    Particulars as to the length of notice to terminate are contained in
       clause 11.

(7)    There are no disciplinary rules applicable to the Executive except as
       provided in this Agreement and if the Executive is dissatisfied with
       any disciplinary decision relating to him he should apply orally or in
       writing to the [Chief Executive Officer/Board].

(8)    Any application for the purpose of seeking redress of any grievance
       relating to the Executive's employment should be made either orally or
       in writing to the [Chief Executive Officer/Board].

(9)    There are no collective agreements relevant to the employment of the
       Executive.

                                       17