<PAGE>

                                                                     EXHIBIT 4.3

Dr Andrew Carr
576 Snowdon Lane
Princeton
New Jersey 08540
United States of America

                                                                 27 January 2003

Dear Andrew,

APPOINTMENT TO THE BOARD OF DIRECTORS OF AMERSHAM PLC

On behalf of Amersham plc (the COMPANY), I am pleased to confirm your
appointment as a director of the Company (the APPOINTMENT) with effect from 9
May 2002. If you have any questions or issues in connection with your
directorship, you are most welcome to raise them at any time.

The purpose of this letter is formally to confirm your appointment and to
provide you with certain details, which I hope you will find helpful in the
discharge of your duties and your understanding of your responsibilities as a
main board director. We have already provided you with a Directors' pack
containing basic corporate documentation, business information and procedures,
which I believe you will find self-explanatory.

APPOINTMENT

1.       The Appointment is subject to the approval of the shareholders.
         Approval will be sought at the next Annual General meeting and
         thereafter every three years. Unless the Appointment is renewed at
         these Annual General Meetings, you undertake to resign as a director of
         the Company forthwith at the conclusion of the meeting.

2.       Notwithstanding the other provisions of this letter, both the board of
         directors of the Company (the BOARD) and the Company are entitled to
         terminate the Appointment at any time in accordance with the provisions
         of the Articles of Association of the Company or the Companies Act 1985
         and, upon such termination or upon your resignation for any reason, you
         shall not be entitled to any damages arising directly or indirectly out
         of any such loss of office and no fee will be payable to you in respect
         of any unexpired portion of the term of the Appointment.

3.       You are considered to be an executive director and will be identified
         as such in the annual report and other documentation.

                                                                              AT
<PAGE>

DUTIES

4.       In your role as Director you have a duty to promote the interests of
         the Company and you share equal responsibility with your co-directors
         for the general management, strategy and overall direction of the
         Company. You have a duty to promote the interests of the Company and to
         ensure the Board exercises effective control over the Group

5.       As a listed public limited company we aim, so far as is practicable, to
         comply with the provisions of the Code of Best Practice published by
         the Turnbull Committee on the Financial Aspects of Corporate
         Governance.

6.       Although other matters may from time to time prevent your attending
         meetings, your input your attendance is generally expected at meetings
         of the Board and any Committee to which you are appointed and at the
         Annual General Meeting.

BOARD MEETINGS

7.       Within the Directors' pack, you will find a schedule of Board meeting
         dates for the year 2002. The full Board meets a minimum seven times a
         year and more often as business needs require.

ANNUAL GENERAL MEETING

8.       Following your appointment to the Board it is necessary for you to be
         re-elected formally at our next Annual General Meeting which will take
         place on Wednesday 7th May 2003 at the Savoy Hotel, London.

FEES

9.       You will be entitled to a fee for your services as a director of the
         Company of L30,000 per annum (less such deductions as the Company is
         required by law to make). The Board will review this fee annually. A
         separate letter is attached summarising the UK tax implications of your
         director's fees.

INSURANCE

10.      To the extent possible, the Company will use its reasonable endeavours
         to maintain appropriate director's and officer's liability insurance
         for your benefit during your Appointment. Such insurance may not cover
         claims in which you are directly or indirectly interested as the
         claimant.

OTHER DIRECTORSHIPS AND BUSINESS INTERESTS

11.      The Company recognises that you may have other duties and business
         interests. However, you will be expected to notify the Chairman of any
         direct conflict of interest that may arise due to your duties as a
         director of the Company and any other duties or business interests that
         you have or may have.

                                                                          Page 2
<PAGE>

12.      During the Appointment you will consult with the Chairman of the
         Company prior to accepting any directorships of publicly quoted
         companies that are in competition with any Group Company or any major
         external appointments. Please notify the Company Secretary immediately
         of any changes in directorships you hold, as these will need to be
         formally noted at the next Board meeting.

EMPLOYMENT AGREEMENT WITH AMERSHAM PHARMACIA BIOTECH (UK) LIMITED (NOW CALLED
AMERSHAM BIOSCIENCES UK LIMITED)

13.      Notwithstanding the Appointment you will continue to be employed under
         your employment agreement with Amersham Pharmacia Biotech (UK) Limited
         (now called Amersham Biosciences UK Limited) dated 1 May 2001 (the
         EMPLOYMENT AGREEMENT) subject to and in accordance with the terms of
         the Employment Agreement, as amended by the letter dated 16 December
         2002, previously sent to you.

14.      For the purposes of this letter GROUP COMPANY shall mean the Company
         any holding company of the Company any subsidiary of the Company or of
         any such holding company and holding company and subsidiary shall have
         the meanings given them by section 736 of the Companies Act 1985 (as
         amended).

FURTHER ADVICE

15.      All Directors shall have access to the advice and services of myself as
         Company Secretary, and I am responsible to the whole Board for ensuring
         that Board procedures and applicable rules and regulations are
         followed.

16.      Should circumstances arise in which it is necessary for you to seek
         independent legal advice, you should feel at liberty to do so. I should
         be happy to recommend from whom such advice might be taken, if you so
         wish, and the Company will be responsible for the costs of such legal
         advice or other professional fees reasonably and properly incurred. You
         might find it helpful to discuss the issue in advance, either with the
         Chairman or with another Non-executive Director, should you think it
         appropriate.

AMERSHAM'S CONSTITUTION

17.      Within the Directors' pack, you will find a copy of the company's
         Memorandum and Articles of Association. You should familiarise yourself
         on its scope and provisions, particularly those relating to Directors.
         If you need any further clarification, please feel free to contact me.

STOCK EXCHANGE REQUIREMENTS

18.      Under the terms of the Company's listing agreement with the UK Listing
         Authority, there are a number of provisions of which you should be
         aware, particularly in relation to the buying and selling of shares by
         Directors and others who are likely from time to time to have
         unpublished price sensitive information. Within the Directors' pack is
         enclosed a copy of a note relating to insider dealing and the UK
         Listing Authority model code for Director's transactions in shares.

                                                                          Page 3
<PAGE>

         There is a separate listing agreement with the Oslo Stock Exchange on
         which we are also listed, and directors are personally required to
         notify the Oslo Stock Exchange of any share dealing with immediate
         effect. You must accordingly follow the procedures for obtaining prior
         consent from the company and notification of the Oslo Stock Exchange
         and the UK Listing Authority, which are all set out in the pack.

INFORMATION FROM YOURSELF

19.      You have already supplied us with information we require relating to
         your shareholding in the Company and your other directorships. Please
         note that if any of the information you have supplied changes, you are
         required to notify us immediately. From time to time, we shall ask you
         to verify that we do hold the latest information about your
         shareholdings and directorships, so that our records are always up to
         date and appropriate notifications may be made.

Please confirm your agreement to the above by signing and returning to me the
enclosed duplicate of this letter.

Yours sincerely

ROBERT ALLNUTT
FOR AND ON BEHALF OF AMERSHAM PLC

I have read and agree to the above terms regarding my appointment as a director
of Amersham plc with effect from 9 May 2002.

________________________                    ________________________
Andrew Carr                                 Date

                                                                          Page 4