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                                                                     EXHIBIT 4.2

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

                                                                 4 December 2002

Dear Andrew,

YOUR EMPLOYMENT AGREEMENT WITH AMERSHAM BIOSCIENCES UK LIMITED (FORMERLY
AMERSHAM PHARMACIA BIOTECH (UK) LIMITED)

We refer to the employment agreement between you and Amersham Biosciences UK
Limited (formerly Amersham Pharmacia Biotech (UK) Limited ("the Company") dated
1 May 2001 (the "Agreement"). As you are aware, the Remuneration Committee has
resolved that with effect from 1 March 2002, in accordance with UK Corporate
Governance practices, all executive directors serving on the Board of Amersham
plc shall be employed on contracts with notice periods not exceeding 12 months.
Following your appointment to the Board of Amersham plc on 9 May 2002, it is
therefore necessary to amend the Agreement as follows:

Section 16.1(a) and Section 16.1(d) shall be deleted and replaced with the
following new Section 16.1(a) and Section 16.1(d):

"(a)     the Executive's resignation of employment on the expiry of 6 months'
prior written notice to the Company;

(d)      termination of the Executive's employment by the Company without cause
on the expiry of 12 months' prior written notice to the Executive."

Section 16.2 shall be deleted and replaced with the following new Section 16.2:
"16.2 Where: (a) the Executive has given notice pursuant to Section 16.1(a); or
(b) the Company has given notice pursuant to Section 16.1(d), the Company may,
in the case of (a) above in its sole discretion at any time, and shall, in the
case of (b) above, no later than three (3) months following the date of the
Company's notice terminate the Executive's employment prior to the end of the
relevant notice period and thereafter make the payment contemplated by Section
16.3.1.

Section 16.3 shall be deleted and replaced with the following new Sections
16.3.1 to 16.3.4:

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"16.3.1  In the event of termination of this Agreement in accordance with
Section 16.2, and except as contemplated by Section 16.4, the Executive will be
entitled to a payment ("the Agreed Payment") equal to 95 percent (95%) of the
sum of:

(a)      the Executive's base salary (calculated by reference to the Executive's
annual base salary at the date of termination of the Employment) for the period
from the effective date of the Executive's termination until the end of the
relevant notice period; and

(b)      10% of the Executive's base salary (calculated by reference to the
Executive's annual base salary at the date of termination) for the period from
the effective date of the Executive's termination until the end of the relevant
notice period. Such payment shall be in respect of all benefits (excluding
pension and bonus) that the Executive would have been entitled to receive during
the relevant notice period; and

(c)      20% of the aggregate of (i) the Executive's base salary (calculated by
reference to the Executive's annual base salary at the date of termination); and
(ii) the Executive's target annual bonus, in each case for the period from the
effective date of the Executive's termination until the end of the relevant
notice period. Such payment shall be in respect of the pension benefits that the
Executive would have been entitled to receive during the relevant notice period;
and

(d)      the average percentage of the annual bonus achieved by the Executive
whilst a Director of Amersham plc in respect of the three complete financial
years of the Company immediately preceding the financial year in which the
Employment terminates, multiplied by the base annual salary of the Executive at
the date of termination of Employment, pro-rated for the period from the
effective date of the Executive's termination until the end of the relevant
notice period. If the Employment terminates before the expiry of three complete
financial years after the date on which the Executive joined the Board of
Amersham plc, the payment shall be the average percentage of (i) the annual
bonus achieved by the Executive whilst a director of Amersham plc in respect of
the complete financial year or years immediately preceding the financial year in
which the Employment terminates, and (ii) the target bonus for the year in which
the Employment terminates, multiplied by the base annual salary of the Executive
at the date of termination of Employment, pro-rated for the period from the
effective date of the Executive's termination until the end of the relevant
notice period. If the Employment terminates before the expiry of a complete
financial year after the date on which the Executive joined the Board of
Amersham plc, the payment shall be the target bonus for the year in which the
Employment terminates, multiplied by the base annual salary of the Executive at
the date of termination of Employment, pro-rated for the period from the
effective date of the Executive's termination until the end of the relevant
notice period.

16.3.2   The Agreed Payment shall be subject to such deductions as may be
required by law and shall be made in 24 equal bi-weekly installments after the
date of termination in accordance with the Company's usual payroll practices
unless such period is shortened pursuant to Section 16.3.4. The Agreed Payment
shall be in full and final settlement of any claims the Executive may have
against the Company, any parent, subsidiary or affiliate of the Company, and
their respective shareholders, directors, officers and employees, arising from
the Employment or the termination thereof save any claim the Executive may have
for personal injury or in respect of any accrued pension rights or rights in
respect of previous awards or grants made under any share option or long term
incentive scheme which shall be determined in accordance with the rules of the
relevant

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scheme(s). At the Company's request, the Executive shall deliver a signed
release as a condition for making the Agreed Payment.

16.3.3   All entitlements to base salary and benefits (under Sections 6, 7, 8, 9
and 10) that are accrued but unpaid as at the date of the termination of the
Employment shall be paid by the Company to the Executive no later than 7 days
after the date of the termination of the Employment. The Company shall pay to
the Executive (except in the event of resignation in accordance with Section
16.1(a) or termination in accordance with Section 16.1(c) a bonus in respect of
the Company's financial year in which the date of termination of the Employment
occurs (and in respect of the previous financial year if not already paid). The
bonus payable under this Section 16.3.3 with respect to the year in which
termination occurs shall be determined by the Remuneration Committee but shall
not be less than the bonus for target performance in relation to the relevant
financial year or, if not yet determined, the previous financial year pro-rated
in respect of the part of the year in which the termination of the Employment
occurs. The Executive will not be entitled to receive any payment in addition to
the Agreed Payment in respect of any holiday entitlement that would have accrued
during the period for which the Agreed Payment is made.

16.3.4   In consideration for the payment of the Agreed Payment, the Executive
agrees to remain bound by the restrictions contained in Section 15 of the
Agreement. For the avoidance of doubt, the Executive shall remain bound by the
restrictions contained in Section 15 for the period of time in which the Company
is paying installments of the Agreed Payment. In the event that the Executive
has resigned and installments of the Agreed Payment are being paid pursuant to
Section 16.3, the Company shall have the option, with the consent of the
Executive, to discontinue paying further installments, in which case the
Executive shall be relieved of further obligations under Section 15 of the
Agreement.

The attached letter clarifies the position relating to your pension entitlement,
which remains unchanged on your appointment as director of Amersham plc.

Would you please confirm that you accept this change to your Agreement by
signing and returning to me the enclosed copy of this letter. All provisions of
the Agreement, except as modified by this amendment will remain in full force
and effect and are hereby reaffirmed. The original should be attached to your
copy of the Agreement.

Yours sincerely

JULIAN COOPER
FOR AND ON BEHALF OF AMERSHAM BIOSCIENCES UK LIMITED

I have read and agree to the above amendments to the Agreement

_________________________                       _________________________
Andrew Carr                                     Date<PAGE>

                                                                    EXHIBIT 4.2a

Mr A Carr
576 Snowdon Lane
Princeton
New Jersey 08540
United States of America

9 September 2002

Dear Andrew

UK PENSION ARRANGEMENTS

In recent months we have had various discussions about your UK pension
arrangements. I am writing now to clarify how the promise made to you at the
time of your departure to the US will be delivered.

At the time of your assignment to the US it was intended that you would remain
in the UK pension arrangements. However, in practice you were enrolled in the US
arrangements and recorded as a leaver from the UK pension plan with effect from
31 December 2000, with an entitlement to a deferred pension. It is now intended
that you will remain in the US retirement arrangements for the remainder of your
employment with Amersham in the US.

On your return to employment with Amersham in the UK your pension benefits will
be as follows:

-        Your active membership of the Amersham Pension Scheme will recommence,
         with your service prior to 31 December 2000 being linked to your salary
         at the time of return and any increases thereafter. This means that
         benefits for all of your UK service will be based on your uncapped
         final salary (and averaged as defined within the rules of the UK plan).

-        You will be eligible for the Key Managers Money Purchase arrangement
         within the approved UK plan, with the contribution rate being that
         appropriate to those at director level. Membership of this Money
         Purchase arrangement may risk your benefits exceeding the maximum
         permitted by the Inland Revenue. This will be examined upon your return
         and, if appropriate, the contribution may be paid instead as a cash
         supplement or to another suitable retirement arrangement.

-        Your total UK benefit on retirement will therefore be the sum of:

         -        your final salary benefit, with both periods of service being
                  based on your latest final salary;

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         -        the proceeds of your Money Purchase arrangement that you
                  accumulated before your move to the US and subsequently on
                  your return; and

         -        the retirement benefits you accumulate during your time with
                  Amersham in the US.

In the event that you do not return to work for Amersham in the UK, your UK
benefits will be as follows:

-        a deferred pension of L57,978.17pa as at 31 December 2000, revalued to
         your date of retirement in accordance with the Plan rules;

-        the proceeds of your Money Purchase arrangement that you accumulated
         prior to your move to the US; and

-        the retirement benefits you accumulate during your time with Amersham
         in the US.

Please note that it if you do not return to the UK to work for Amersham then
these deferred benefits are likely to be greater than the maximum permitted by
the Inland Revenue. This would mean that not all of your benefit could be paid
from the approved plan, so the company would pay the shortfall to you directly.

Finally, please note that the UK pension Trustee's records may not accurately
reflect the promise that was made to you at the time of moving to the US. We are
currently corresponding with the Trustee to rectify this.

Yours sincerely,

GEORGE BATTERSBY
GROUP HUMAN RESOURCES DIRECTOR

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