THIS THIRD SUPPLEMENTAL DEED is made this 7th day of August 1998

BETWEEN:-

1.       HUNTINGDON LIFE SCIENCES LIMITED, a Company incorporated under the laws
         of England and Wales with  registered  number  1815730 of Woolley Road,
         Alconbury, Huntingdon, Cambridgeshire PE17 5HS (the "Chargor"); and

2.       NATIONAL  WESTMINSTER  BANK Plc of 3rd Floor,  Juno Court,  25 Prescott
         Street, London E1 8BB as agent and trustee for the Secured Parties (the
         "Agent" which  expression  shall include all successor agents appointed
         from time to time).

WHEREAS

(A)      By a  Facilities  Agreement  of even date  herewith  made  between  the
         Chargor (1),  Huntingdon  Life Sciences  Group Plc (the  "Parent") (2),
         Huntingdon Life Sciences Inc. (3), the Secured Parties  (therein called
         the "Banks") (4) and the Agent (5) ("the  Facilities  Agreement"),  the
         Banks  have  agreed to make  available  to the  Borrowers  (as  therein
         defined) certain facilities in substitution for the Existing Facilities
         (as therein defined);

(B)      The Existing  Facilities,  the Existing  Ancillary  Facilities  and the
         Bridging Facility (as defined in the Facilities Agreement) are the only
         facilities  which  immediately  prior to the  signing of this Deed were
         available  to the  Borrowers  from the  Banks or any of them  (alone or
         jointly with any other person);

(C)      This  Deed is  supplemental  to a  Guarantee  and  Debenture  dated 1st
         November 1995 between the parties  hereto (as amended and  supplemented
         by  Supplemental  Deeds dated 20th January 1998 and 26th February 1998,
         together hereinafter referred to as "the Debenture").

NOW THIS DEED WITNESSETH as follows:-


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1.       (a)      In this Deed (including the recitals),  unless the context
                  otherwise requires or unless otherwise defined or provided for
                  in this  Deed,  words  and  expressions  shall  have  the same
                  meanings as are  attributable  to them under the Debenture and
                  the Facilities Agreement; and

         (b)      Clause 2.1 of the Debenture  shall be amended by the insertion
                  of the words  "when and to the  extent  that they fall due for
                  payment" after the words "that it will".

2.       The  right  of the  Agent to give  notice  and to take  possession  and
         appoint a Receiver  pursuant  to Clause 7.1 of the  Debenture  shall be
         exercisable  only in  accordance  with  Clause  13.4 of the  Facilities
         Agreement.

3.       The provisions of Clause 7.2 of the Debenture shall,  subject to Clause
         8 below,  have effect only if,  following a breach of Clause 12.3(a) of
         the  Facilities  Agreement  which  constitutes  a Default  under Clause
         13.1(b)  thereof or  following a Default  described  in Clause  13.1(f)
         thereof,  the  Agent  gives  notice  pursuant  to  Clause  13.2  of the
         Facilities Agreement and a Receiver or Receivers are appointed over the
         whole of the property, assets and undertaking of any of the Borrowers.

4.       The Agent may only serve  notice and  exercise  its rights under Clause
         10.1 of the Debenture if it has given notice in accordance  with Clause
         13.2 of the Facilities Agreement.

5.       The Agent may only serve  notice and  exercise  its rights under Clause
         11.1 of the Debenture  after notice has been given in  accordance  with
         Clause  13.2  of  the  Facilities  Agreement  OR,  in  the  case  of an
         application  to the  Court  for an  administration  order,  only in the
         circumstances described in Clause 13.1(j) of the Facilities Agreement.

6.       Without  prejudice to any set-off pursuant to insolvency  legislation
         and  notwithstanding  any other  provisions of the Debenture or this
         Deed,  neither the Agent nor the Secured Parties (or any of them)
         shall have (i) any right  whether  under  Clause 14 of the  Debenture
         or otherwise howsoever  to  combine,  consolidate, set off or transfer
         (save for a transfer  pursuant  to Clause 14.2.3 of the  Facilities
         Agreement)  any sums from time to time standing to the credit
         of any  account of the  Chargor with the  Agent,  transferred from the
         Deposit  Account  and intended to be used for the  Chargor's  general
         working  capital  requirements,  ("a  Relevant Account") or (ii) any
         rights or remedies over a Relevant Account save for the exercise of the
         Agent's rights under the Debenture in accordance with the provisions
         of Clause 8 below.

7.       The  provisions of Clause 23 of the  Debenture  shall be subject to any
         provisions  inconsistent  therewith in the Facilities Agreement,  which
         latter provisions shall prevail.

8.       Notwithstanding any of the provisions of this Deed or the Debenture:-

         (a)      none of the rights,  powers and remedies  granted to the Agent
                  pursuant to the Debenture  shall be exercisable in relation to
                  the  sums  from  time  to time  standing  to the  credit  of a
                  Relevant Account; and

         (b)      the Chargor shall be entitled at all times to withdraw  monies
                  from a Relevant  Account  for the  Chargor's  general  working
                  capital requirements;

         unless (i) the Agent has made a demand for  payment  pursuant to Clause
         13.2 of the  Facilities  Agreement  and has  appointed  a  Receiver  or
         Receivers over the whole of the property, assets and undertaking of any
         of the  Borrowers  pursuant to Clause 11.1 of the  Debenture as amended
         hereby OR (ii) an administration order has been made in relation to any
         of the Borrowers  pursuant to section 8 of the  Insolvency Act 1986 (or
         any statutory notification or re-enactment thereof from time to time in
         force).

9.       In the event of any inconsistency between the provisions hereof and the
         provisions of the Facilities Agreement the latter shall prevail.

10.      Subject to the provisions  hereof the Debenture shall continue in full
         force and effect.

11.      This Deed shall be governed by and construed and interpreted in
         accordance with English law.

12.      Every provision  contained in this Deed shall be severable and distinct
         from every other such  provision  and if at any time any one or more of
         such provisions is or becomes invalid,  illegal or  unenforceable,  the
         validity,  legality and enforceability of the remaining such provisions
         shall not in any way be affected thereby.

13.      This Deed may be  executed in any number of  counterparts  and all such
         counterparts shall be deemed to constitute one and the same instrument.

IN WITNESS  whereof  the  Chargor  and the Agent have signed this Deed as a deed
with the intention that it be delivered the day and year first before written.

Signed as a Deed by                 )
HUNTINGDON LIFE SCIENCES LIMITED    )
acting by two Directors or one      )
Director and its secretary          )



Signed as a Deed for and on behalf of   )
NATIONAL WESTMINSTER BANK PLC           )