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                                                                  EXHIBIT 4.1(o)

                               SERVICE AGREEMENT

                            DATED 29TH OCTOBER 2004

                                (1) VERNALIS PLC

                                (2) JOHN SLATER


                                 ALLEN & OVERY

                                     London
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                                    CONTENTS

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CLAUSE                                                                                PAGE
<S>                                                                                   <C>
1.     Definitions..................................................................    2
2.     Appointment..................................................................    2
3.     Duties.......................................................................    2
4.     Other Activities.............................................................    3
5.     Place of Performance.........................................................    3
6.     Remuneration.................................................................    3
7.     Expenses.....................................................................    4
8.     Car..........................................................................    4
9.     Hours of Work/Holiday........................................................    4
10.    Sickness/Injury..............................................................    4
11.    Pension/Life Insurance/Medical Insurance.....................................    5
12.    Grievances/Disciplinary Decisions............................................    5
13.    Confidentiality..............................................................    5
14.    Protection of Interests of the Company.......................................    6
15.    Inventions...................................................................    6
16.    Publicity....................................................................    7
17.    Liquidation/Amalgamation.....................................................    7
18.    Default......................................................................    8
19.    Termination..................................................................    8
20.    Change of Control............................................................    9
21.    Additional Particulars.......................................................    9
22.    Term and Termination.........................................................    9
23.    Continuing Terms.............................................................    9
24.    Notices......................................................................    9
25.    Entire Agreement.............................................................    9
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THIS AGREEMENT is made the 29th day of October 2004

BETWEEN:

(1)   VERNALIS PLC (registered number 2304992) whose registered office is
      situated at Oakdene Court, 613 Reading Road, Winnersh, Wokingham,
      Berkshire RG41 5UA (THE COMPANY); and

(2)   JOHN SLATER of Woodlands, Mays Hill, Worplesdon, Guilford, Surrey GU3 3RJ
      (THE DIRECTOR).

NOW IT IS HEREBY AGREED as follows:

1.    DEFINITIONS

      In this Agreement the following expressions shall have the following
      meanings:

      SUBSIDIARY means any company which for the time being is a subsidiary
      company (as such expression is defined by Section 736 of the Companies Act
      1985 as amended by Section 144 of the Companies Act 1989) of any other
      company;

      ASSOCIATED COMPANY means any company which for the time being is a holding
      company (as such expression is defined by Section 736 of the Companies Act
      1985 as amended by Section 144 of the Companies Act 1989) of the Company
      or any subsidiary of any such holding company;

      THE BOARD means the Board of Directors of the Company;

      TERMINATION DATE means the date on which the employment of the Director
      under this Agreement shall terminate for whatever reason irrespective of
      whether the Company shall have been in breach of this Agreement.

2.    APPOINTMENT

2.1   The Director shall be appointed General Counsel of the Company (which
      shall be deemed to be his job title for the purposes of this Agreement and
      of the Employment Rights Act 1996) unless amended by a letter in writing
      from the Company.

2.2   The appointment may be terminated by either party giving to the other not
      less than 12 calendar months prior notice in writing.

2.3   The Director will be appointed a Director of the Company and will remain
      so during the period of his employment by the Company.

3.    DUTIES

      During the continuance of his engagement hereunder the Director shall:

      (a)   be responsible for corporate development and associated activities,
            legal services, including those of Company Secretary;

      (b)   perform such duties and exercise such powers, authorities and
            discretions consistent with his role of General Counsel as the
            Company's Chief Executive Officer or the

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            Board shall from time to time delegate to him on such terms and
            conditions and subject to such restrictions as the Chief Executive
            Officer or the Board may from time to time reasonably impose;

      (c)   use his best endeavours to promote the interests of the Company and
            those of its Subsidiary and Associated Companies for the time being
            and shall during normal business hours unless prevented by illness
            or other incapacity devote the whole of his time, attention and
            abilities to the business and affairs of the Company and its
            Subsidiary and Associated Companies, if any, for the time being;

      (d)   in the discharge of such duties and in the exercise of such powers
            observe and comply with all relevant resolutions, regulations and
            directions from time to time made or given by the Board.

      (e)   act as an officer of any Subsidiary or Associated Company or hold
            any other appointment or office as nominee or representative of the
            Company or any Subsidiary or Associated Company as directed by the
            Board.

4.    OTHER ACTIVITIES

      The Director shall not during the continuance of this Agreement without
      the consent of the Board (such consent not to be unreasonably withheld or
      delayed) directly or indirectly engage in any other business or be
      concerned or interested (within the meaning contained in Part VI of the
      Companies Act 1985) in the share capital of any other business save that
      he may be interested (defined as aforesaid) as a holder or beneficial
      owner of not more than five per cent. (5%) of any class of stock shares or
      debentures which are listed on any publicly quoted market.

5.    PLACE OF PERFORMANCE

      The Director's duties hereunder shall be performed at the Company's head
      office or at such other place as the Chief Executive Officer or Board
      shall from time to time reasonably direct and further the Chief Executive
      Officer or Board shall be at liberty to appoint the Director to serve any
      of its Subsidiary or Associated Companies if any for the time being
      (without further remuneration unless otherwise agreed) in his capacity as
      General Counsel.

6.    REMUNERATION

      As remuneration for his services hereunder the Director shall be entitled
      to a basic salary payable at the rate of two hundred and twenty five
      thousand pounds sterling ((pound)225,000) per annum (exclusive of any
      bonus award, pension contribution or share option grant which may from
      time to time be made by the Board) payable in equal monthly instalments
      (and proportionately for any lesser period each monthly instalment being
      deemed to accrue rateably from day to day) on the last day of every
      calendar month in arrears. Such remuneration shall be inclusive of any
      fees payable to him as a Director or other officer of the Company or of
      its Subsidiary or Associated Companies if any for the time being. The
      salary payable hereunder shall be variable upwards by decision of the
      Board and subject to review during the month of April 2005 and at least
      once in each financial year thereafter. The Company may in its absolute
      discretion award to the Director a non-pensionable annual cash bonus of up
      to a maximum of 60 per cent. of base salary dependant upon the achievement
      of performance targets which will be notified to the Director by the Board
      of Directors of Vernalis plc.

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7.    EXPENSES

      The Company shall pay to the Director all reasonable travelling
      entertainment and other expenses incurred by him in the performance of his
      duties under this Agreement. The Director shall, on being so required,
      provide the Company with vouchers or other evidence of actual payment of
      such expenses.

8.    CAR

      The Director will receive a non pensionable cash car allowance of
      (pound)12,600 per annum.

9.    HOURS OF WORK/HOLIDAY

9.1   The Director shall perform such hours of work as may from time to time be
      reasonably required of him and shall not be entitled to receive any
      additional remuneration for work outside his normal hours which said
      normal hours shall for statutory purposes be deemed to be from 9.00 am to
      5.30 pm Monday to Thursday inclusive and 9.00 am to 4.15 pm on Friday.

9.2   The Director shall be entitled during every calendar year to a minimum of
      thirty (30) working days holiday in addition to bank or public holidays in
      the UK, or to such longer holidays as shall from time to time be agreed by
      the Board, during which his remuneration hereunder shall continue to be
      payable. Holidays shall be taken at such times as the Director and the
      Company's Chief Executive Officer shall consider most convenient having
      regard to the requirements of the Company's business. Holiday entitlement
      during the calendar year in which the Director's employment commences and
      ceases will be based on his length of service in the calendar year in
      question and will be proportionate to the whole year's entitlement. Up to
      five days holiday may be carried forward to the next holiday year but no
      further. On termination of employment the Director will be made a payment
      in respect of accrued but untaken holiday for that holiday year.

10.   SICKNESS/INJURY

10.1  In the event that the Director shall at any time be prevented by illness
      or other incapacity from properly performing his duties hereunder (and
      shall if required furnish the Board with evidence satisfactory to them of
      such incapacity) he shall be entitled to receive his full salary for the
      first six (6) months and one half of his full salary for the next
      consecutive period of six (6) months during which such incapacity shall
      continue;

10.2  Any salary received by the Director pursuant to the foregoing Clause 10.1
      shall be inclusive of any payment which the Company is required to make in
      respect of Statutory Sick Pay. The Director shall keep the Company
      informed of the amount of any National Health Insurance sickness or injury
      benefits to which he is entitled (whether or not these are received) and
      which are not covered by Statutory Sick Pay and a deduction of the amount
      of such benefit will be made by the Company from any salary payable under
      the Clause 10.1;

10.3  Notwithstanding the provisions of Clause 2.2 of this Agreement, if the
      Director shall continue so incapacitated for a longer period than twelve
      (12) consecutive months or if he shall be so incapacitated at different
      times for more than twelve (12) months in any one period of eighteen (18)
      consecutive months then and in either of such cases the Company shall be
      entitled forthwith to terminate the engagement of the Director by notice
      in writing and thereupon the Director shall have no claim against the
      Company in respect of such termination. The length of the said notice to
      be given to the Director hereunder shall be the minimum period permitted
      by statute and dependent upon his length of service. The Company may not
      exercise its power to terminate the engagement of the Director under this

                                        4
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      clause 10.3 if the Director is, at the relevant time, in receipt of
      benefits under the income protection cover referred to in clause 11.4
      below.

11.   PENSION/LIFE INSURANCE/MEDICAL INSURANCE

11.1  The Director shall be informed in writing whether a contracting out
      certificate is in force in respect of the employment of the Director.

11.2  The Director shall be entitled to receive a total monthly contribution
      payable by the Company into one or more appropriate pension schemes
      established by the Company, or into a personal pension scheme nominated by
      the Director, at a rate of 19% of a basic salary variable upwards by
      decision of the Board. Alternatively, at the Director's option and on such
      terms as may be agreed with the Company, the Company shall pay the
      Director an additional monthly cash allowance in lieu of all or part of
      any pension contributions by the Company less tax and National Insurance,
      provided this does not result in any additional cost to the Company. For
      the avoidance of doubt, this allowance shall not be taken into account in
      relation to the calculation of any salary related benefits.

11.3  While this Agreement continues a lump sum benefit shall be payable on the
      Director's death to such beneficiaries identified by the Director in any
      expression of his wishes delivered to the Company before his death. The
      benefit is equal to four times the Director's basic annual salary at his
      death.

11.4  The Director (and his spouse and dependant children living in the UK)
      shall be entitled to receive private health care. The Director shall also
      be entitled to income protection cover equivalent to 3/4 of basic salary
      (minus the State Incapacity Benefit). These benefits will be subject to
      the terms of the insurance or other arrangements under which the benefits
      are provided.

12.   GRIEVANCES/DISCIPLINARY DECISIONS

      Without prejudice to any rights he may have under this Agreement or
      operation of law should the Director have any question or grievance or be
      dissatisfied with any disciplinary decision concerning his employment
      hereunder, he should refer it to the Board whose decision shall be final
      and binding.

13.   CONFIDENTIALITY

13.1  In respect of Confidential Information of the Company or any Subsidiary or
      Associated Company, the Director will not, unless authorised to do so by
      the Board or by the Company's Chief Executive Officer or by a Court of
      competent jurisdiction, during the continuance of his employment or for a
      period of five (5) years thereafter:

      (a)   use Confidential Information for his own benefit or the benefit of
            any other person; or

      (b)   disclose Confidential Information to any person; or

      (c)   through any failure to exercise all reasonable care and diligence
            cause any disclosure of Confidential Information to any person.

13.2  Confidential Information shall include any information relating to
      research and development projects, inventions, processes, practical
      experience and methodology, technical and scientific data, specifications
      and formulae (whether or not patented or patentable) developed or acquired
      and owned or used by the Company any Subsidiary or Associated Company for
      the

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      subject of research, production programmes, lists or details of
      transactions of, or related to, the Company any Subsidiary or Associated
      Company with customers, commercial relationships (including collaboration
      agreements) of, or related to, the Company any Subsidiary or Associated
      Company, finances, business developments and future business strategy of,
      or related to, the Company any Subsidiary or Associated Company which the
      Company has designated as confidential from time to time. Confidential
      Information shall not include information which is in the public domain
      otherwise than by virtue of breach of obligations to the Company or any
      Subsidiary or Associated Company.

13.3  The Company may from time to time notify the Director of any additional
      categories of information with regard to the businesses or activities of
      the Company, Subsidiary or Associated Company which it regards as
      confidential and which will be the subject to the restrictions in this
      Clause.

14.   PROTECTION OF INTERESTS OF THE COMPANY

14.1  Until the expiration of 12 months from the termination of the Agreement
      the Director will not directly or indirectly solicit or entice away or
      endeavour to entice away from the Company, any Subsidiary or Associated
      Company any person employed by the Company or that Subsidiary or
      Associated Company in any executive, sales, marketing, research, or
      technical support capacity as at the date of the termination of this
      Agreement in order to procure that such a person be engaged or employed by
      any other company.

14.2  After the termination of this Agreement or, if later, the date of his
      ceasing to be a Director of the Company, the Director will not represent
      himself or permit himself to be held out as being in any way connected
      with or interested in the business of the Company; and after the
      termination of this Agreement he will not represent himself or permit
      himself to be held out as being in any way connected with the business of
      any Subsidiary or Associated Company, except if and for so long as he
      remains a director or an employee of that Subsidiary or Associated
      Company.

15.   INVENTIONS

15.1  If at any time during the continuance of his employment the Director
      whether alone or with any other person, makes, discovers or develops any
      invention, product, process or idea which relates to or affects, or is
      capable of being used or adapted for use in or in connection with, the
      business or any product, process or intellectual property right of the
      Company or any Subsidiary or Associated Company, the invention, product,
      process, or idea will be the absolute property of the Company (except to
      the extent, if any, provided otherwise by Section 39 of the Patents Act
      1977).

15.2  The Director will promptly and fully disclose to the Company any and all
      inventions, products, processes, and ideas relating in any way to the
      actual or projected products, business or affairs of the Company or any
      Subsidiary or Associated Company and made or discovered wholly or partly
      by the Director during the period of the Director's employment by the
      Company.

15.3  All other intellectual property including original work, industrial and
      artistic designs, copyrights, trade marks and Confidential Information,
      relating to the business of the Company, any Subsidiary or Associated
      Company composed, written, made, designed, or discovered by the Director
      in the course of his employment with the Company shall belong, exclusively
      to the Company.

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15.4  The Director will, at the request and expense of the Company, do all
      things and sign all documents deemed by the Company necessary or
      appropriate:

      (a)   to confirm or vest in the Company or any nominee of the Company all
            rights, interest and title in and to the Company's inventions and
            the intellectual property referred to in Clause 15.3;

      (b)   to procure for the Company or its nominees, patent, design,
            copyright, trade mark or other protection for the Company's
            inventions and the intellectual property referred to in Clause 15.3
            in the United Kingdom of Great Britain and Northern Ireland and in
            such territories as the Company may in its absolute discretion from
            time to time direct; and

      (c)   to assign to the Company or its nominees the right to make
            application for patent, design, copyright, trade mark or other
            protection for the Company's inventions and the intellectual
            property referred to in Clause 15.3 under the laws of territories
            outside the United Kingdom of Great Britain and Northern Ireland
            and/or under any treaty or international convention and to claim for
            such applications whatever priority rights may be lawful.

15.5  Except insofar as the provisions of the Patents Act 1977 apply, the
      Director's employment by the Company and the remuneration received as one
      of its employees shall constitute his sole right of compensation for the
      performance of his obligations herein contained.

15.6  If the Director ceases to be employed by the Company and enters the
      employment of any Associated Company or of any company which purchases the
      whole or part of any of the businesses of the Company or any such
      Associated Company, the Company may assign its rights under this Clause to
      such Associated Company or purchaser in which event Clauses 15.1 to 15.7
      of this Agreement shall (save for the enforcement by the previous employer
      of its rights hereunder) thenceforth be construed as if the expression the
      Company means such new employer.

15.7  There are no inventions or discoveries now owned wholly or partly by the
      Director which were made at a time when the Director was not employed by
      the Company, other than as disclosed in writing to the Company.

16.   PUBLICITY

      The Director shall not knowingly or recklessly at any time make any untrue
      statement in relation to the Company or any Subsidiary or Associated
      Companies and in particular shall not after the termination of this
      Agreement wrongfully represent himself as being employed by or connected
      with the Company or any Subsidiary or Associated Companies.

17.   LIQUIDATION/AMALGAMATION

      If before the expiration of this Agreement the employment of the Director
      hereunder shall be terminated by reason of the liquidation of the Company
      for the purpose of amalgamation or reconstruction or as part of any
      arrangement for the amalgamation of the undertaking of the Company not
      involving liquidation the Director shall be offered employment with the
      amalgamated or reconstructed company on terms not less favourable than the
      terms of this Agreement.

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18.   DEFAULT

      If the Director shall be guilty of any serious misconduct or any serious
      or (after due warning) persistent breach or non-observance of any of the
      conditions of this Agreement or shall neglect fail or refuse to carry out
      the duties properly assigned to him hereunder or shall become bankrupt or
      compound with his creditors, the Company shall be entitled summarily to
      terminate his employment hereunder without notice and the Director shall
      have no claim against the Company in respect of such termination
      notwithstanding anything contained elsewhere in this Agreement provided
      always that if any such act of misconduct or such breach or non-observance
      is capable of being remedied, the Director shall first be offered a
      reasonable opportunity to remedy the same prior to termination as
      aforesaid and, if and when so remedied, the employment of the Director
      hereunder shall continue without interruption.

19.   TERMINATION

19.1  This Agreement may be terminated by mutual agreement between the parties
      at any time or by either party giving 12 months notice in writing to the
      other.

19.2  On the termination of his employment for whatever reason the Director will
      promptly:

      (a)   resign (if he has not already done so) from all offices held by him
            in the Company and any Subsidiaries or Associated Companies; and

      (b)   deliver up to the Company all technical information, lists of
            customers, correspondence, documents and other property (including
            any car) relating to the business of the Company, any Subsidiary or
            Associated Company which may be in his possession or under his
            control; and

      (c)   The Director irrevocably authorises the Company in his name and on
            his behalf to execute all documents and to all things necessary to
            effect the resignations referred to in Clause 19.2 in the event of
            his failure to do so.

19.3  Any termination of the employment of the Director will be without
      prejudice to his continuing obligations under this Agreement.

19.4  The Company has the right to suspend any of the Director's duties and
      powers during any period after notice of termination of the Agreement has
      been given by the Company or the Director. In particular, the Company may
      exercise this right where the Director resigns from the Company's
      employment in circumstances where it is reasonable for the Company to
      believe that he is or is about to become concerned in, or about to
      commence, a business which is, or is likely to be, competitive with any
      part of the business of the Company or any Associated or Subsidiary
      Company with which the Director was substantially engaged or concerned in
      the 12 months before the suspension started. Throughout any such period of
      suspension the Director's salary, pro rata bonus at a rate equivalent to
      the average bonus paid to him over the past three years and benefits to
      which he is entitled under this Agreement shall continue to be paid or
      provided by the Company. At any time during such period the Director will,
      at the request of the Board, immediately resign, without claim for
      compensation, his office as a director of the Company and any directorship
      or other office held by him in the Company or any Associated or Subsidiary
      Company. The period for which the restriction in Clause 14.1 applies shall
      be reduced by any other period over which the Company exercises its powers
      to suspend any of the Director's duties and powers under Clause 19.4.

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20.   CHANGE OF CONTROL

20.1  The Director shall be entitled at any time within six months after a
      Change in Control of the Company to terminate his employment by giving to
      the Company not less than 30 days prior notice in writing. Upon such
      termination or upon termination without notice by the Company during such
      six month period the Director shall be entitled to receive a payment
      forthwith by way of liquidated damages equal to 12 (twelve) times the
      Director's then monthly basic salary. The parties hereto agree that the
      sum set out in this sub-clause is a genuine pre-estimate of the Director's
      loss.

20.2  For the purposes of Clause 20.1 "Change of Control" of the Company shall
      take place on the date on which one person or a group of persons acting in
      concert holds, directly or indirectly, any shares in the Company which
      carry fifty per cent (50%) or more of the then voting rights of the
      Company and a Change of Control shall be deemed to have taken place upon
      Completion.

21.   ADDITIONAL PARTICULARS

      The following additional particulars are given for the purposes of the
      Employment Rights Act 1996:

      (a)   except as otherwise provided by this Agreement, there are no terms
            or conditions of employment relating to hours of work or to normal
            working hours or to entitlement to holidays (including public
            holidays) or holiday pay or to incapacity for work due to sickness
            or injury or to pensions or pension schemes.

22.   TERM AND TERMINATION

      This Agreement shall remain in full force and effect until such time as
      the Director's employment by the Company as defined in Clause 2.1 shall
      terminate for any reason, whereupon this Agreement will terminate.

23.   CONTINUING TERMS

      The expiration or determination of this Agreement howsoever arising shall
      not operate to affect such of the provisions hereof as in accordance with
      their terms are expressed to operate or have effect thereafter and shall
      be without prejudice to any right or action already accrued to either
      party in respect of any breach of this Agreement by the other party.

24.   NOTICES

      Any notice to be given hereunder shall be in writing and be sufficiently
      served, in the case of the Director, by being delivered either personally
      to him or sent by registered post addressed to him at his usual or last
      known place of abode or, in the case of the Company, by being delivered at
      or sent by registered post or recorded delivery addressed to the Company's
      Chief Executive Officer at the Company's Registered Office and any such
      notice if so posted shall be deemed served three days following that on
      which it was posted and in proving such service it shall be sufficient to
      prove that the notice was properly addressed and dispatched.

25.   ENTIRE AGREEMENT

      The terms of this Agreement constitute the entire agreement and
      understanding between the parties hereto.

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IN WITNESS whereof the parties hereto have executed this Agreement as a Deed the
day and year first above written.

VERNALIS PLC                        )
executed this Agreement as a        )
Deed in the presence of:            )

                                          Director    /s/ Simon Sturge

                                          Director    /s/ A J Weir

Executed as a Deed by               )
JOHN SLATER                         )                 /s/ JAD Slater
in the presence of:                 )

/s/ A January
    ***

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