STOCK OPTION AGREEMENT

                  STOCK  OPTION  AGREEMENT,  dated  as of  June  21,  1999  (the
"Agreement")  by  and  between  Trenwick  Group  Inc.,  a  Delaware  corporation
("Trenwick"),  and Chartwell Re Corporation, a Delaware corporation ("Chartwell"
or the "Issuer").

                  WHEREAS,  concurrently with the execution and delivery of this
Agreement,  Trenwick and  Chartwell  are entering  into an Agreement and Plan of
Merger,  dated as of the date hereof (the "Merger  Agreement"),  which provides,
among other things,  upon the terms and subject to the conditions  thereof,  for
the merger of Chartwell with and into  Trenwick,  with Trenwick as the surviving
corporation (the "Merger"); and

                  WHEREAS,  as a condition to  Trenwick's  willingness  to enter
into the Merger  Agreement,  Trenwick has requested  that Chartwell  agree,  and
Chartwell  has so  agreed,  to grant to  Trenwick  an option to  purchase  up to
1,918,729  shares of  common  stock,  par value  $.01 per  share,  of  Chartwell
("Chartwell  Common  Stock")  in  accordance  with the terms and  subject to the
conditions set forth herein.

                  NOW,  THEREFORE,  to induce  Trenwick to enter into the Merger
Agreement, and in consideration of the foregoing and the mutual representations,
warranties,  covenants  and  agreements  set  forth  herein  and in  the  Merger
Agreement, the parties hereto agree as follows:

               1.  Grant of  Option.  Subject  to the terms and  conditions set
forth herein,  Chartwell  hereby grants to Trenwick an  irrevocable  option
(the  "Chartwell  Option") to purchase up to 1,918,729 (as adjusted as set forth
herein) shares (the "Option  Shares") of Chartwell  Common Stock (such number of
Option  Shares  representing  19.9% of the number of shares of Chartwell  Common
Stock issued and  outstanding  on the date hereof) in the manner set forth below
at a price (the  "Exercise  Price") of $23.82 per Option  Share (which price per
share is equal to the product of the Conversion Number (as defined in the Merger
Agreement) and the closing price per share of Trenwick  common stock,  par value
$.01 per share,  on the Nasdaq Stock Market National Market on the date hereof),
payable  in cash in  accordance  with  Section  4  hereof.  Notwithstanding  the
foregoing, in no event shall the number of Option Shares for which the Chartwell
Option is  exercisable  exceed  19.9% of the  number of issued  and  outstanding
shares of Chartwell Common Stock.  Capitalized terms used herein but not defined
herein shall have the meanings set forth in the Merger Agreement.

                2.  Exercise of Option. The Chartwell Option may be exercised by
Trenwick,  in whole or in part,  at any time or from time to time after the
Merger Agreement becomes terminable by Trenwick under  circumstances which would
or could  entitle  Trenwick to receive the  Termination  Fee pursuant to Section
5.14(b) of the Merger Agreement (a "Trigger  Event")  (regardless of whether the
Merger  Agreement  is  actually  terminated  or whether  there  occurs a closing
involving  Chartwell);  provided,  that a Trigger  Event  shall not occur in the
circumstances  contemplated by Section 5.14(b)(z) of the Merger Agreement unless
and until a Termination Fee shall be payable  pursuant to Section  5.14(b)(z) of
the Merger  Agreement.  In the  event Trenwick  wishes to exercise the Chartwell




Option,  Trenwick  shall  deliver to  Chartwell a written  notice (an  "Exercise
Notice")  specifying  the total  number of Option  Shares it wishes to purchase.
Each closing of a purchase of Option Shares (an "Option  Closing")  shall occur,
but subject to the satisfaction or waiver of the conditions set forth in Section
3 hereof,  at a place,  on a date and at a time  designated  by  Trenwick  in an
Exercise  Notice  delivered at least two business  days prior to the date of the
Option  Closing.  The Chartwell  Option shall terminate upon the earlier of: (i)
the Effective  Time;  (ii) the  termination of the Merger  Agreement  other than
under  circumstances  which also  constitute a Trigger Event; or (iii) the 180th
day following a Trigger  Event (or if, at the  expiration of such 180 day period
the Chartwell  Option cannot be exercised by reason of any applicable  judgment,
decree,  order,  law or  regulation,  10 business days after such  impediment to
exercise  shall have been  removed or shall have become final and not subject to
appeal,  but in no event  under  this  clause  (iii)  later  than the  365th day
following such Trigger  Event).  Notwithstanding  the  foregoing,  the Chartwell
Option may not be  exercised  if Trenwick  is in  material  breach of any of its
representations or warranties,  or in material breach of any of its covenants or
agreements,  contained in this  Agreement or in the Merger  Agreement.  Upon the
giving by Trenwick to  Chartwell  of the  Exercise  Notice and the tender of the
applicable  aggregate  Exercise Price, but subject to the satisfaction or waiver
of the conditions set forth in Section 3 hereof,  Trenwick shall be deemed to be
the  holder  of  record  of the  Option  Shares  issuable  upon  such  exercise,
notwithstanding  that the stock transfer books of Chartwell shall then be closed
or that certificates  representing such Option Shares shall not then be actually
delivered to Trenwick.

                3. Conditions to Closing. The obligation of Chartwell to issue
the Option Shares to Trenwick hereunder is subject to the conditions, which
(other than the  conditions  described in clauses (i), (iii) and (iv) below) may
be waived by Chartwell in its sole discretion,  that (i) all waiting periods, if
any,  under  the HSR  Act,  applicable  to the  issuance  of the  Option  Shares
hereunder  shall have expired or have been  terminated;  (ii) the Option  Shares
shall  have  been  approved  for  listing  on the NYSE upon  official  notice of
issuance;  (iii)  all  consents,  approvals,  orders  or  authorizations  of, or
registrations,  declarations  or  filings  with,  any  federal,  state  or local
administrative   agency  or  commission  or  other   federal,   state  or  local
Governmental  Entity,  if any,  required in connection  with the issuance of the
Option  Shares  hereunder  shall have been  obtained or made, as the case may be
including, without limitation, by Trenwick; and (iv) no preliminary or permanent
injunction or other order or decree by any court of competent jurisdiction,  law
or regulation  prohibiting  or otherwise  restraining  such issuance shall be in
effect.

               4.       Payment and Delivery of Certificates.

               (a) At any  Option  Closing,  Trenwick  shall  pay to  Chartwell
the aggregate purchase price (equal to the Exercise Price multiplied by the
number of Option  Shares to be purchased at such Option  Closing) for the shares
of Chartwell  Common Stock  purchased  pursuant to the exercise of the Chartwell
Option  in  immediately  available  funds  by wire  transfer  to a bank  account
designated in writing by Chartwell;  provided,  however, that failure or refusal
of  Chartwell  to  designate  such  account  shall not  preclude  Trenwick  from
exercising the Chartwell Option.

                                       -2-



               (b) At any Option  Closing,  simultaneously  with the  delivery
of immediately  available funds as provided in Section 4(a), Chartwell will
deliver to Trenwick a certificate  or  certificates  representing  the number of
Option Shares to be purchased by Trenwick at such Option  Closing,  which Option
Shares will be free and clear of all liens, claims,  charges and encumbrances of
any kind whatsoever and if the option is exercised in part only, Chartwell shall
deliver a new option  evidencing the rights of Trenwick  thereof to purchase the
balance of the shares  purchasable  hereunder  and (ii) Trenwick will deliver to
Chartwell a copy of this Agreement and a letter  agreeing that Trenwick will not
offer to sell or otherwise dispose of such shares in violation of applicable law
or the provisions of this Agreement. If at the time of issuance of Option Shares
pursuant  to an  exercise  of the  option  hereunder,  Chartwell  shall not have
redeemed the Chartwell Rights, or shall have issued any similar securities, then
each Option Share issued  pursuant to such exercise will also  represent  such a
corresponding Chartwell Right or new rights with terms substantially the same as
and at least as favorable to Trenwick as are  provided in the  Chartwell  Rights
Agreement or similar agreement then in effect. Chartwell shall pay all expenses,
and any and all United States  federal,  state and local taxes and other charges
that may be payable in connection  with the  preparation,  issue and delivery of
stock certificates under this Section 4 in the name of Trenwick or its designee.

               5. Representations and Warranties of Chartwell. Chartwell hereby
represents  and warrants to Trenwick  that (a)  Chartwell is a  corporation
duly  organized,  validly  existing and in good  standing  under the laws of the
State of Delaware and has the  corporate  power and authority to enter into this
Agreement, (b) the execution and delivery of this Agreement by Chartwell and the
consummation by Chartwell of the transactions contemplated hereby have been duly
authorized  by all  necessary  corporate  action on the part of Chartwell and no
other corporate  proceedings on the part of Chartwell are necessary to authorize
this  Agreement  or  any of  the  transactions  contemplated  hereby,  (c)  this
Agreement has been duly executed and delivered by Chartwell, constitutes a valid
and binding  obligation of Chartwell and, assuming this Agreement  constitutes a
valid and binding  obligation of Trenwick,  is enforceable  against Chartwell in
accordance  with its terms,  (d)  Chartwell  has taken all  necessary  corporate
action to authorize  and reserve for  issuance  and to permit it to issue,  upon
exercise of the Chartwell Option,  and at all times from the date hereof through
the expiration of the Chartwell Option will have reserved,  1,918,729 authorized
and unissued Option Shares,  such amount being subject to adjustment as provided
in Section 9, all of which,  upon their issuance and delivery in accordance with
the  terms  of  this  Agreement,   will  be  validly  issued,   fully  paid  and
nonassessable,  (e) upon  delivery  of the Option  Shares to  Trenwick  upon the
exercise of the Chartwell  Option,  Trenwick will acquire the Option Shares free
and clear of all claims, liens, charges,  encumbrances and security interests of
any nature  whatsoever,  and (f) none of  Chartwell,  any of its  affiliates  or
anyone acting on its or their behalf has issued, sold or offered any security of
Chartwell  to any person under  circumstances  that would cause the issuance and
sale of the Option Shares,  as contemplated by this Agreement,  to be subject to
the  registration  requirements  of the  Securities Act as in effect on the date
hereof and, assuming the  representations  of Trenwick contained in Section 6(d)
are true and correct and based on Trenwick's  commitment in its letter  referred
to in Section 4 hereof,  the  issuance,  sale and delivery of the Option  Shares
hereunder  would  be  exempt  from  the  registration  and  prospectus  delivery
requirements  of the  Securities  Act,  as in  effect  on the date  hereof  (and
Chartwell  shall not take any action  which would cause the  issuance,  sale and
delivery  of  the  Option   Shares   hereunder   not  to  be  exempt  from  such
requirements).

                                       -3-


               6.   Representations and Warranties of Trenwick.  Trenwick
represents  and  warrants to Chartwell  that (a) Trenwick is a  corporation
duly  organized,  validly  existing and in good  standing  under the laws of the
State of Delaware and has the  corporate  power and authority to enter into this
Agreement  and to carry out its  obligations  hereunder,  (b) the  execution and
delivery of this Agreement by Trenwick and the  consummation  by Trenwick of the
transactions  contemplated  hereby have been duly  authorized  by all  necessary
corporate  action on the part of Trenwick and no other corporate  proceedings on
the part of Trenwick are  necessary to  authorize  this  Agreement or any of the
transactions  contemplated hereby, (c) this Agreement has been duly executed and
delivered  by  Trenwick  and  constitutes  a valid  and  binding  obligation  of
Trenwick,   and,  assuming  this  Agreement  constitutes  a  valid  and  binding
obligation of Chartwell,  is enforceable against Trenwick in accordance with its
terms,  and (d) any Option Shares acquired upon exercise of the Chartwell Option
will be acquired for  Trenwick's own account,  for investment  purposes only and
will not be, and the Chartwell Option is not being,  acquired by Trenwick with a
view to the public distribution thereof in violation of any applicable provision
of the Securities Act.

               7.   Restrictions on Transfer.

               (a)  Restrictions  on Transfer.  Prior to the first  anniversary
of the date on which  Trenwick  purchases any Option Shares  hereunder (the
"Expiration Date"), Trenwick shall not, directly or indirectly,  by operation of
law or otherwise,  sell, assign, pledge, or otherwise dispose of or transfer any
Option  Shares  acquired by Trenwick  pursuant  to this  Agreement  ("Restricted
Shares") beneficially owned by it, other than in accordance with Section 7(b) or
Section 8. Subsequent to the Expiration  Date,  Trenwick shall not,  directly or
indirectly, by operation of law or otherwise,  sell, assign, pledge or otherwise
dispose of or transfer any  Restricted  Shares  beneficially  owned by it to any
purchaser,  assignee,  pledgee or other transferee who would,  immediately after
such sale, assignment,  pledge,  disposition or transfer,  beneficially own more
than 4.9% of the then  outstanding  voting power of the issuer of the Restricted
Shares,  except in  accordance  with Section 7(b) or Section 8 and other than in
market transactions at prevailing prices.

               (b) Permitted Sales. Following the termination of the Merger
Agreement,  Trenwick  shall be permitted to sell or transfer any Restricted
Shares  beneficially  owned by it if such sale is made  pursuant  to a tender or
exchange  offer or merger that has been  approved or  recommended,  or otherwise
determined  to be fair  to and in the  best  interests  of the  shareholders  of
Chartwell,  by a majority of the members of the Board of  Directors of Chartwell
(which  majority shall include a majority of directors who were directors  prior
to the announcement of such tender or exchange offer or merger).

                                       -4-


               8.  Registration Rights.  Following the termination of the Merger
Agreement,  but not later than the second anniversary of the last date that
Trenwick  acquired Option Shares under this  Agreement,  Trenwick (a "Designated
Holder") may by written  notice (the  "Registration  Notice") to Chartwell  (the
"Registrant") request the Registrant to register under the Securities Act all or
any part of the Restricted  Shares  beneficially  owned by the Designated Holder
(the  "Registrable   Securities")  pursuant  to  a  bona  fide  firm  commitment
underwritten public offering in which the Designated Holder and the underwriters
shall  effect  as wide a  distribution  of  such  Registrable  Securities  as is
reasonably  practicable and shall use their  commercially  reasonable efforts to
prevent  any  person  (including  any  Group  (as used in Rule  13d-5  under the
Exchange  Act))  and  its  affiliates  from  purchasing  through  such  offering
Restricted Shares  representing more than 1% of the outstanding shares of common
stock of the Registrant on a fully diluted basis (a "Permitted  Offering").  The
Registration  Notice  shall  include a  certificate  executed by the  Designated
Holder and its proposed  managing  underwriter,  which  underwriter  shall be an
investment  banking firm of  nationally  recognized  standing  (the  "Manager"),
stating  that (i) they  have a good  faith  intention  to  commence  promptly  a
Permitted  Offering and (ii) the Manager in good faith believes  that,  based on
the then prevailing market  conditions,  it will be able to sell the Registrable
Securities  at a per share  price  equal to at least 80% of the then Fair Market
Value (as  defined  below) of such  shares.  The  Registrant  (and/or any person
designated by the  Registrant)  shall  thereupon have the option  exercisable by
written notice delivered to the Designated  Holder within 10 business days after
the receipt of the Registration Notice,  irrevocably to agree to purchase all or
any  part of the  Registrable  Securities  proposed  to be so sold for cash at a
price (the "Option Price") equal to the product of (i) the number of Registrable
Securities  to be so purchased by the  Registrant  and (ii) the then Fair Market
Value of such  shares.  Any  such  purchase  of  Registrable  Securities  by the
Registrant (or its designee)  hereunder shall take place at a closing to be held
at the principal  executive  offices of the  Registrant or at the offices of its
counsel at any reasonable date and time designated by the Registrant and/or such
designee in such notice within 20 business  days after  delivery of such notice.
Any payment for the shares to be purchased shall be made by delivery at the time
of such  closing of the Option Price in  immediately  available  funds.  As used
herein,  the "Fair Market  Value" of any share shall be the average of the daily
closing  sales price for such share on the NYSE during the 10 NYSE  trading days
prior to the fifth NYSE trading day preceding the date such Fair Market Value is
to be determined.
                  If the  Registrant  does not  elect  to  exercise  its  option
pursuant to this Section 8 with respect to all Registrable Securities,  it shall
use its commercially  reasonable  efforts to effect, as promptly as practicable,
the  registration  under  the  Securities  Act  of the  unpurchased  Registrable
Securities proposed to be so sold;  provided,  however,  that (i) Trenwick shall
not be  entitled  to  more  than  an  aggregate  of two  effective  registration
statements  hereunder and (ii) the  Registrant  will not be required to file any
such  registration  statement  during  any period of time (not to exceed 90 days
after such  request in the case of clauses  (A),  (B) or (C) below) when (A) the
Registrant  is  in  possession  of  material  non-public  information  which  it
reasonably  believes  would be  detrimental to be disclosed at such time and, in
the  opinion of counsel to the  Registrant,  such  information  would have to be
disclosed  if a  registration  statement  were  filed  at  that  time;  (B)  the
Registrant is required  under the Securities  Act to include  audited  financial
statements  for any period in such  registration  statement  and such  financial
statements are not yet available for inclusion in such  registration  statement;
or  (C)  the  Registrant  determines,  in its  reasonable  judgment,  that  such
registration  would interfere with any financing,  acquisition or other material
transaction  involving the Registrant or any of its  affiliates.  The Registrant
shall  use its  reasonable  best  efforts  to cause any  Registrable  Securities
registered  pursuant  to this  Section  8 to be  qualified  for sale  under  the
securities or blue sky laws of such  jurisdictions as the Designated  Holder may
reasonably  request and shall continue such  registration  or  qualification  in
effect in such jurisdiction; provided, however, that the Registrant shall not be
required to qualify to do business in, or consent to general  service of process
in, any jurisdiction by reason of this provision.

                                       -5-



                  The  registration  rights  set  forth  in this  Section  8 are
subject to the condition that the Designated Holder shall provide the Registrant
with such information with respect to such holder's Registrable Securities,  the
plans for the distribution  thereof,  and such other information with respect to
such holder as, in the  reasonable  judgment of counsel for the  Registrant,  is
necessary to enable the Registrant to include in such registration statement all
material  facts  required  to  be  disclosed  with  respect  to  a  registration
thereunder.

                  A registration effected under this Section 8 shall be effected
at the Registrant's expense,  except for underwriting  discounts and commissions
and the fees and the  expenses  of counsel  to the  Designated  Holder,  and the
Registrant  shall  provide to the  underwriters  such  documentation  (including
certificates,  opinions of counsel and "comfort"  letters from  auditors) as are
customary in connection with underwritten  public offerings as such underwriters
may reasonably  require.  In connection with any such registration,  the parties
agree (i) to indemnify each other and the  underwriters in the customary  manner
(provided that the Designated  Holder shall only be required to indemnify  other
parties  to  such  underwriting  agreement  for  information  relating  to  such
Designated  Holder  and  supplied  by it  for  inclusion  in  such  registration
statement),  (ii) to enter into an underwriting  agreement in form and substance
customary  for  transactions  of such  type  with  the  Manager  and  the  other
underwriters  participating  in such  offering  and  (iii) to take  all  further
actions which shall be reasonably necessary to effect such registration and sale
(including,  if the  Manager  deems it  necessary,  participating  in road  show
presentations).

                  The  Registrant  shall be entitled to include (at its expense)
additional  shares of its common stock in a  registration  effected  pursuant to
this  Section  8 only if and to the  extent  the  Manager  determines  that such
inclusion will not adversely affect the prospects for success of such offering.

                 9.  Adjustment  upon  Changes  in  Capitalization.  Without
limitation to any  restriction on Chartwell  contained in this Agreement or
in the Merger Agreement, in the event of any change in Chartwell Common Stock by
reason of stock dividends, split-ups, mergers, recapitalizations,  subdivisions,
conversions,  combinations,  exchange of shares or the like, the type and number
of shares or securities  subject to the Chartwell Option, and the Exercise Price
per Option  Share  provided  in Section 1, shall be  adjusted  appropriately  to
restore to Trenwick its rights  hereunder,  including the right to purchase from
the Chartwell (or its successors)  shares of Chartwell Common Stock representing
19.9% of the outstanding Chartwell Common Stock for the aggregate Exercise Price
calculated as of the date of this Agreement as provided in Section 1.

                                       -6-


               10.  Restrictive  Legends.  Each  certificate representing shares
of  Chartwell  Common Stock issued to Trenwick at a Closing will have typed
or printed thereon a restrictive legend in substantially the following form:

                           THE SECURITIES  REPRESENTED BY THIS  CERTIFICATE HAVE
         NOT BEEN REGISTERED  UNDER THE SECURITIES ACT OF 1933, AS AMENDED,  AND
         MAY BE REOFFERED OR SOLD ONLY IF SO REGISTERED OR IF AN EXEMPTION  FROM
         SUCH  REGISTRATION  IS AVAILABLE.  SUCH  SECURITIES ARE ALSO SUBJECT TO
         ADDITIONAL  RESTRICTIONS  ON TRANSFER AS SET FORTH IN THE STOCK  OPTION
         AGREEMENT,  DATED AS OF JUNE 21,  1999, A COPY OF WHICH MAY BE OBTAINED
         FROM THE ISSUER UPON REQUEST.

                  It is  understood  and agreed that:  (i) the  reference to the
resale  restrictions  of the Securities Act in the above legend shall be removed
by delivery of substitute  certificate(s)  without such reference if such Option
Shares have been  registered  pursuant to the Securities Act, such Option Shares
have  been  sold in  reliance  on and in  accordance  with  Rule 144  under  the
Securities  Act or Trenwick  has  delivered to Chartwell a copy of a letter from
the staff of the Securities and Exchange  Commission,  or an opinion of counsel,
in form and substance  satisfactory to Chartwell and its counsel,  to the effect
that such legend is not required for purposes of the  Securities  Act;  (ii) the
reference to  restrictions  pursuant to this Agreement in the above legend shall
be removed by delivery of substitute  certificate(s)  without such  reference if
the Option Shares  evidenced by  certificate(s)  containing  such reference have
been sold or transferred in compliance with the provisions of this Agreement and
under  circumstances  that do not require the retention of such  reference;  and
(iii) the legend  shall be  removed in its  entirety  if the  conditions  in the
preceding  clauses  (i)  and  (ii)  are  both  satisfied.   In  addition,   such
certificate(s)  shall  bear  any  other  legend  as  may  be  required  by  law.
Certificates  representing  shares sold in a registered public offering pursuant
to Section 8 shall not be required to bear the legend set forth in this  Section
10.

               11. Profit Limitation.

               (a)  Notwithstanding  any  other  provision  of  this  Agreement
or the Merger  Agreement,  in no event shall  Trenwick's  Total  Profit (as
hereinafter  defined) exceed $9.0 million (such amount, the "Profit Limit") and,
if it would otherwise exceed such amount, Trenwick, at its sole election, shall,
within five  business  days,  either (i) deliver to the Issuer for  cancellation
Option  Shares  (valued,  for  purposes of this Section 11, at their Fair Market
Value on the date of such  delivery),  (ii) pay cash to the  Issuer or refund in
cash any  Termination  Fee  previously  paid to  Trenwick or reduce or waive the
amount of any Termination Fee payable to Trenwick pursuant to Section 5.14(b) of
the Merger  Agreement,  or (iii)  undertake  any  combination  thereof,  so that
Trenwick's  Total  Profit  shall not exceed the Profit  Limit after  taking into
account  the  foregoing  actions.  As used  herein,  "Total  Profit"  means  the
aggregate amount (before taxes) of (i) the amount of Termination Fee received by
Trenwick  pursuant  to  Section  5.14(b)  of the  Merger  Agreement  and any fee
received by Trenwick  pursuant to Section  5.14(c) of the Merger  Agreement  and
(ii) (x) the net cash  amounts  received  by  Trenwick  pursuant  to the sale of
Option  Shares  (or any other  securities  into  which  such  Option  Shares are
converted or exchanged) to any unaffiliated  party, less (y) Trenwick's purchase
price for such Option Shares.

                                       -7-


               (b)  Notwithstanding  any  other  provision  of  this  Agreement
     or the Merger  Agreement,  the Chartwell  Option may not be exercised for a
number of Option  Shares  that  would,  as of the date of the  Exercise  Notice,
result in a Notional  Total  Profit (as  hereinafter  defined)  of more than the
Profit Limit and, if exercise of the Chartwell Option otherwise would exceed the
Profit Limit,  Trenwick, at its discretion,  may increase the Exercise Price for
that  number  of Option  Shares  set  forth in the  Exercise  Notice so that the
Notional Total Profit shall not exceed the Profit Limit; provided,  that nothing
in this sentence shall restrict any exercise of the Chartwell  Option  permitted
hereby on any  subsequent  date at the  Exercise  Price  set forth in  Section 1
hereof.  As used herein,  the term  "Notional  Total Profit" with respect to any
number of  Option  Shares as to which  Trenwick  may  propose  to  exercise  the
Chartwell  Option  shall be the Total  Profit  determined  as of the date of the
Exercise Notice  assuming that the Chartwell  Option were exercised on such date
for such number of Option Shares and assuming that such Option Shares,  together
with all  other  shares of  Chartwell  Common  Stock  held by  Trenwick  and its
subsidiaries as of such date, were sold for cash at the closing market price for
the Chartwell  Common Stock on the NYSE  Composite Tape at the close of business
on the preceding trading day (less customary brokerage commissions).

               12. Binding Effect; No Assignment; No Third Party Beneficiaries.
This  Agreement  shall be  binding  upon and  inure to the  benefit  of the
parties hereto and their respective  successors and permitted  assigns.  Neither
this  Agreement  nor the rights or the  obligations  of either  party hereto are
assignable, except by operation of law, or with the written consent of the other
party.  Nothing contained in this Agreement,  express or implied, is intended to
confer  upon any person  other  than the  parties  hereto  and their  respective
permitted  assigns any rights or remedies of any nature  whatsoever by reason of
this  Agreement.  Any Restricted  Shares sold by a party in compliance  with the
provisions of Section 8 shall,  upon  consummation  of such sale, be free of the
restrictions  imposed with respect to such shares by this Agreement,  unless and
until such party shall  repurchase or otherwise  become the beneficial  owner of
such  shares,  and any  transferee  of such shares  shall not be entitled to the
registration rights of such party.

               13. Specific Performance. The parties recognize and agree that if
for any reason any of the provisions of this Agreement are not performed in
accordance  with their specific terms or are otherwise  breached,  immediate and
irreparable  harm or injury would be caused for which money damages would not be
an adequate  remedy.  Accordingly,  each party agrees that, in addition to other
remedies,  the other party shall be entitled to an  injunction  restraining  any
violation or threatened  violation of the provisions of this  Agreement.  In the
event that any action  should be brought in equity to enforce the  provisions of
the  Agreement,  neither  party will allege,  and each party  hereby  waives the
defense, that there is adequate remedy at law.

               14. Entire  Agreement.  This  Agreement,  the Merger  Agreement
(including  any exhibits  and  schedules  thereto) and the  Confidentiality
Agreement  constitute  the  entire  agreement,  and  supersede  all other  prior
agreements and  understandings,  both written and oral, between the parties with
respect to the subject matter of this Agreement.

                                       -8-


               15.  Further  Assurances.  Each party will  execute and deliver
all such further documents and instruments and take all such further action
as may be necessary in order to consummate the transactions contemplated hereby.

               16.  Validity.  The  invalidity  or  unenforceability  of any
provision of this Agreement shall not affect the validity or enforceability
of the other provisions of this Agreement,  which shall remain in full force and
effect. In the event any court or other competent authority holds any provisions
of this Agreement to be null,  void or  unenforceable,  the parties hereto shall
negotiate  in good faith the  execution  and  delivery of an  amendment  to this
Agreement  in  order,  as nearly  as  possible,  to  effectuate,  to the  extent
permitted  by law,  the  intent  of the  parties  hereto  with  respect  to such
provision and the economic effects thereof.  If for any reason any such court or
regulatory  agency determines that Trenwick is not permitted to acquire the full
number of shares of Chartwell  Common Stock provided in Section 1 hereof (as the
same  may be  adjusted),  it is the  express  intention  of  Chartwell  to allow
Trenwick to acquire such lesser number of shares as may be permissible,  without
any amendment or modification  hereof.  Each party agrees that, should any court
or other competent authority hold any provision of this Agreement or part hereof
to be null,  void or  unenforceable,  or  order  any  party  to take any  action
inconsistent  herewith,  or not take any action required herein, the other party
shall not be entitled to specific  performance  of such provision or part hereof
or to any other remedy,  including but not limited to money damages,  for breach
hereof or of any other  provision of this Agreement or part hereof as the result
of such holding or order.

               17. Notices.  All notices,  requests, claims,  demands and other
communications under this Agreement shall be in writing and shall be deemed
given if (i) delivered,  personally,  or (ii) sent by overnight  courier service
(providing proof of delivery), or (iii) telecopied (which is confirmed), or (iv)
five days after being mailed by  registered  or certified  mail (return  receipt
requested) to the parties at the  following  addresses (or at such other address
for a party as shall be specified by like notice):

                  If to Trenwick:

                      Alan L. Hunte
                      Vice President and
                         Chief Financial Officer
                      Trenwick Group Inc.
                      One Canterbury Green
                      Stamford, CT  06901
                      Fax:  (203) 353-5544


                  with a copy to:

                      Baker & Mc Kenzie
                      805 Third Avenue
                      New York, New York 10022
                      Attention:  James R. Cameron
                      Fax:  (212) 891-3835



                                       -9-


                  If to Chartwell, to:

                      President
                      Chartwell Re Corporation
                      Four Stamford Plaza
                      107 Elm Street
                      Stamford, CT  06902
                      Fax:  (203) 705-2710

                  with a copy to:

                      LeBoeuf, Lamb, Greene & MacRae, L.L.P.
                      125 West 55th Street
                      New York, New York  10019
                      Attention:  Robert S. Rachofsky
                      Fax: (212) 424-8500

               18.  Governing Law;  Choice of Forum.  This Agreement  shall be
governed by, and  construed in  accordance  with,  the laws of the State of
Delaware without regard to the conflicts of law principles thereof.  Each of the
parties hereto (a) consents to submit itself to the personal jurisdiction of any
federal  court  located in the State of Delaware or any Delaware  state court in
the event any dispute  arises out of this  Agreement or any of the  transactions
contemplated by this  Agreement,  (b) agrees that it will not attempt to deny or
defeat such personal  jurisdiction by motion or other request for leave from any
such court and (c) agrees  that it will not bring any  action  relating  to this
Agreement or any of the transactions contemplated by this Agreement in any court
other than a federal court sitting in the state of Delaware or a Delaware  state
court.

               19.  Interpretation.  When a reference  is made in this Agreement
to a Section, such reference shall be to a Section of this Agreement unless
otherwise indicated. Whenever the words "include", "includes" or "including" are
used in this  Agreement,  they  shall be  deemed  to be  followed  by the  words
"without   limitation."  The  descriptive   headings  herein  are  inserted  for
convenience  of  reference  only and are not intended to be part of or to affect
the meaning or interpretation of this Agreement.

               20.  Counterparts. This Agreement may be executed in one or more
counterparts,  each of which shall be deemed to be an original, but both of
which, taken together, shall constitute one and the same instrument.

               21.  Expenses.  Except as otherwise  expressly  provided herein
or in the Merger  Agreement,  all costs and expenses incurred in connection
with the transactions  contemplated by this Agreement shall be paid by the party
incurring such expenses.

                                      -10-


               22.  Amendment.  This  Agreement may not be amended,  except by
an instrument in writing signed on behalf of each of the parties.

               23.  Extension;  Waiver.  Any  agreement  on the part of a party
to  waive  any  provision  of this  Agreement,  or to  extend  the time for
performance,  will be valid only if set forth in an instrument in writing signed
on behalf of such party.  The failure of any party to this  Agreement  to assert
any of its rights under this Agreement or otherwise will not constitute a waiver
of such rights.

               24.  Loss or  Mutilation.  Upon  receipt by  Chartwell  of
evidence reasonably  satisfactory to it of the loss, theft,  destruction or
mutilation of this Agreement, and (in the case of loss, theft or destruction) of
reasonably satisfactory indemnification,  and upon surrender and cancellation of
this Agreement,  if mutilated,  Chartwell will execute and deliver to Trenwick a
new  Agreement  of like  tenor and date.  Any such new  Agreement  executed  and
delivered will  constitute an additional  contractual  obligation on the part of
Chartwell, whether or not the Agreement so lost, stolen, destroyed, or mutilated
shall at any time be enforceable by anyone.



                                      -11-




                  IN WITNESS  WHEREOF,  the  parties  hereto  have  caused  this
Agreement to be executed by their respective duly authorized  officers as of the
date first above written.

                                              TRENWICK GROUP INC.

                                              By:    /s/ James F. Billett, Jr.
                                              ----------------------------------
                                              Name:  James F. Billett, Jr.
                                              Title: Chairman, President and
                                                     Chief Executive Officer


                                              CHARTWELL RE CORPORATION

                                              By:    /s/ Richard E. Cole
                                              ----------------------------------
                                              Name:   Richard E. Cole
                                              Title:  Chairman and Chief
                                                      Executive Officer