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                                                                     Exhibit 4.3

                                    FORM OF

                                MASTER AGREEMENT

                                    BETWEEN

                             ALLEGHANY CORPORATION

                                      AND

                     DARWIN PROFESSIONAL UNDERWRITERS, INC.

                        Dated as of ______________, 2006

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                                TABLE OF CONTENTS

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ARTICLE I DEFINITIONS....................................................     1
   1.1    Certain Definitions............................................     1

ARTICLE II FINANCIAL AND OTHER INFORMATION...............................     4
   2.1    Financial Information and Public Documents.....................     4
   2.2    Internal Control / Audit.......................................     8
   2.3    Board Meetings.................................................     9
   2.4    Corporate Compliance Program...................................     9

ARTICLE III CERTAIN MATTERS..............................................    10
   3.1    Amended and Restated Certificate of Incorporation and Amended
          and Restated Bylaws............................................    10
   3.2    The Initial Public Offering....................................    10
   3.3    Covenant Not to Take Certain Actions Affecting Alleghany.......    10
   3.4    Adoption of Stockholder Rights Plan............................    10
   3.5    Dilutive Issuances.............................................    10
   3.6    Repurchase of Common Stock.....................................    11

ARTICLE IV OTHER AGREEMENTS..............................................    11
   4.1    Further Assurances.............................................    11
   4.2    Insurance Matters..............................................    11
   4.3    Indemnification................................................    12
   4.4    Investment Management..........................................    12
   4.5    Allocation of Costs and Expenses...............................    12
   4.6    Charter Provision..............................................    13
   4.7    Alleghany Policies.............................................    13

ARTICLE V MISCELLANEOUS..................................................    13
   5.1    Governing Law; Consent to Jurisdiction; Waiver of Jury Trial...    13
   5.2    Survival of Covenants..........................................    14
   5.3    Notices........................................................    14
   5.4    Severability...................................................    14
   5.5    Entire Agreement...............................................    15
   5.6    Amendment......................................................    15
   5.7    Rules of Construction..........................................    15
   5.8    Counterparts...................................................    15
   5.9    Specific Performance...........................................    16
   5.10   Further Assurances.............................................    16
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                                    FORM OF

                                MASTER AGREEMENT

          MASTER AGREEMENT, dated as of ___________, 2006 (this "Agreement"), by
and between Alleghany Corporation, a Delaware corporation ("Alleghany") and
Darwin Profession Underwriters, Inc., a Delaware corporation ("DPUI"). Certain
terms used in this Agreement are defined in Section 1.1.

                                   WITNESSETH:

          WHEREAS, as of the date hereof, Alleghany, through its wholly-owned
subsidiary Alleghany Insurance Holdings LLC, owns approximately 90% of the
issued and outstanding voting securities of DPUI; and

          WHEREAS, DPUI has previously filed the IPO Registration Statement (as
herein defined) with the Securities and Exchange Commission but it has not yet
become effective; and

          WHEREAS, immediately following the consummation of the Initial Public
Offering (as herein defined), Alleghany will continue to own more than 50% of
the outstanding voting securities of DPUI; and

          WHEREAS, Alleghany may in the future further reduce its equity
ownership of DPUI; and

          WHEREAS, it is appropriate and desirable to set forth the agreements
that will, following the consummation of the Initial Public Offering, govern
certain matters relating to the Initial Public Offering and the relationship of
Alleghany, DPUI and their respective Subsidiaries (as herein defined).

          NOW, THEREFORE, in consideration of the premises and the covenants and
agreements contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, and intending to be
legally bound hereby, the parties hereby agree as follows:

                                    ARTICLE I

                                   DEFINITIONS

          1.1 Certain Definitions. For purposes of this Agreement, the following
terms shall have the meanings specified in this Section 1.1:

          "Affiliate" (and, with a correlative meaning, "affiliated") means,
with respect to any Person, any direct or indirect subsidiary of such Person,
and any other Person that directly, or through one or more intermediaries,
controls or is controlled by or is under common control with such first Person;
provided, however, that from and after the Closing Date, no member of the DPUI
Group shall be deemed an Affiliate of any member of the Alleghany Group for
purposes of this Agreement and no member of the Alleghany Group shall be deemed
an Affiliate of any member of the DPUI Group for

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purposes of this Agreement. As used in this definition, "control" (including
with correlative meanings, "controlled by" and "under common control with")
means possession, directly or indirectly, of power to direct or cause the
direction of management or policies or the power to appoint and remove a
majority of directors (whether through ownership of securities or partnership or
other ownership interests, by contract or otherwise).

          "Alleghany Audit Committee" means the Audit Committee of the Alleghany
Board.

          "Alleghany Auditors" means the independent certified public
accountants of Alleghany.

          "Alleghany Board" means the Board of Directors of Alleghany.

          "Alleghany Designated Officer" means either of the Senior Vice
President - Finance and Investments or the Vice President - Finance of
Alleghany.

          "Alleghany Group" means Alleghany and each Person (other than any
member of the DPUI Group) that, at any time of determination, is a Subsidiary of
Alleghany.

          "Alleghany Representatives" means the officers and directors of
Alleghany and Persons designated by them (including without limitation legal
counsel and other professional advisors) to act on behalf of Alleghany.

          "Business Day" means a day other than a Saturday, Sunday or other day
on which commercial banks in New York City are authorized or required by Law to
close. Any event the scheduled occurrence of which would fall on a day that is
not a Business Day shall be deferred until the next succeeding Business Day.

          "Capitol Companies" means, collectively, Capitol Insurance
Corporation, Capitol Specialty Insurance Corporation, and Platte River Insurance
Company.

          "CEO" means, with respect to either Alleghany or DPUI, its chief
executive officer.

          "CFO" means, with respect to either Alleghany or DPUI, its chief
financial officer.

          "Closing Date" means the closing of the Initial Public Offering.

          "Common Stock" means the common stock, [$0.01] par value per share, of
DPUI.

          "DPUI Audit Committee" means the Audit Committee of the DPUI Board.


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          "DPUI Auditors" means the independent certified public accountants of
DPUI.

          "DPUI Board" means the Board of Directors of DPUI.

          "DPUI Group" means, at any time of determination, DPUI and each
Subsidiary of DPUI.

          "Effective Time" means the time that the IPO Registration Statement is
declared effective by the SEC.

          "Exchange Act" shall mean the Securities Exchange Act of 1934, as
amended, and the rules and regulations of the SEC thereunder, all as the same
shall be in effect at the time that reference is made thereto.

          "GAAP" means United States generally accepted accounting principles.

          "Governmental Authority" means any entity exercising executive,
legislative, judicial, regulatory or administrative functions of or pertaining
to government, including any governmental authority, agency, department, board,
commission or instrumentality whether federal, state, local or foreign (or any
political subdivision thereof), and any tribunal, court or arbitrator(s) of
competent jurisdiction.

          "Initial Public Offering" means the initial public offering of the
Common Stock.

          "IPO Registration Statement" means the registration statement on Form
S-1 filed under the Securities Act (No. 333-132355) pursuant to which the Common
Stock to be sold in the Initial Public Offering will be registered, including
the Prospectus related thereto, amendments and supplements to the Registration
Statement, including post-effective amendments, all exhibits and all materials
incorporated by reference in the Registration Statement and Prospectus.

          "Law" means any federal, state, local or foreign law (including common
law), statute, code, ordinance, rule, regulation or other requirement enacted,
promulgated, issued or entered by a Governmental Authority.

          "NYSE Arca" means NYSE Arca Exchange or, if the Common Stock at any
time shall not be traded on the NYSE Acra Exchange, then such securities
exchange (including for this purpose the NASDAQ National Market) on which the
Common Stock is then traded.

          "Person" means any individual, corporation, partnership, firm, joint
venture, association, joint-stock company, trust, unincorporated organization,
Governmental Authority or other entity.

          "Prospectus" means the prospectus or prospectuses included in the
Registration Statement, as amended or supplemented by any prospectus supplement
and


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<PAGE>

by all other amendments and supplements to any such prospectus, including
post-effective amendments and all material incorporated by reference in such
prospectus or prospectuses.

          "Purchase Agreement" means the Purchase Agreement to be entered into
by and among DPUI and the Underwriters in connection with the offering of Common
Stock by DPUI in the Initial Public Offering.

          "Registration Rights Agreement" means the Registration Rights
Agreement to be entered into by and between Alleghany Insurance Holdings LLC and
DPUI, substantially in the form filed or to be filed as an exhibit to the IPO
Registration Statement.

          "SEC" means the Securities and Exchange Commission.

          "Securities Act" means the Securities Act of 1933, as amended.

          "Subsidiary" or "subsidiary" means, with respect to any Person, any
corporation, limited liability company, joint venture or partnership of which
such Person (a) beneficially owns, either directly or indirectly, more than
fifty percent (50%) of (i) the total combined voting power of all classes of
voting securities of such entity, (ii) the total combined equity interests, or
(iii) the capital or profit interests, in the case of a partnership; or (b)
otherwise has the power to vote, either directly or indirectly, sufficient
securities to elect a majority of the board of directors or similar governing
body.

          "Tax Sharing Agreement" means the Tax Sharing Agreement, dated as of
January 1, 2005, entered into by and between Alleghany Insurance Holdings LLC
and DPUI.

          "Underwriters" means the managing underwriters for the Initial Public
Offering.

                                   ARTICLE II

                         FINANCIAL AND OTHER INFORMATION

          2.1 Financial Information and Public Documents. DPUI agrees that if
Alleghany is required during or for any fiscal year, in accordance with GAAP, to
account for its investment in DPUI on a consolidated basis or under the equity
method of accounting, then in respect of such fiscal year:

          (a) Fiscal Year. DPUI shall, and shall cause each of its consolidated
subsidiaries to, maintain a fiscal year which commences on January 1 and ends on
December 31 of each calendar year.

          (b) Monthly Financial Information. DPUI shall furnish to Alleghany a
Monthly President's Report, containing monthly financial and other information,
in such


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form and detail, and within the time periods, as are specified by the Alleghany
Designated Officer consistent with the requirements then applicable to other
Subsidiaries of Alleghany regarding such reports.

          (c) Monthly, Quarterly and Annual Financial Information. DPUI shall
furnish to Alleghany a Subsidiary Reporting Package containing monthly,
quarterly or annual financial and other information and data with respect to
DPUI and its Subsidiaries and their businesses, properties, financial position,
results of operations and prospects, in such form and detail, and within the
time periods, as are specified by the Alleghany Designated Officer consistent
with the requirements then applicable to other Subsidiaries of Alleghany
regarding such reporting packages.

          (d) Alleghany Public Filings. DPUI shall cooperate fully, and shall
use reasonable efforts to cause the DPUI Auditors to cooperate fully, with
Alleghany to the extent requested by Alleghany in the preparation of Alleghany's
press releases, public earnings releases, Quarterly Reports on Form 10-Q, Annual
Reports to Stockholders, Annual Reports on Form 10-K (the Annual Reports to
Stockholders and the Annual Reports on Form 10-K, collectively "the Alleghany
Annual Statements"), any Current Reports on Form 8-K and any amendments to any
of the foregoing and any other proxy, information and registration statements,
reports, notices, prospectuses and any other filings made by Alleghany with the
SEC, any national securities exchange or otherwise made publicly available
(collectively, "Alleghany Public Filings"). In connection with the Alleghany
Public Filings, DPUI agrees:

          (i) to provide to Alleghany all information that Alleghany requests in
     connection with any such Alleghany Public Filings or that, in the judgment
     of Alleghany's legal department, is required to be disclosed therein under
     any Law. Without limiting the generality of the foregoing, DPUI will
     provide all required financial information with respect to it and its
     consolidated Subsidiaries to the Alleghany Auditors and management in
     sufficient and reasonable time and in sufficient detail to permit the
     Alleghany Auditors to take all steps and perform all review necessary, and
     to provide sufficient assistance to the Alleghany Auditors, with respect to
     information to be included or contained in the Alleghany Public Filings;

          (ii) to use its best efforts to provide such information in a timely
     manner to enable Alleghany to prepare, print and release such Alleghany
     Public Filings on such date as Alleghany shall determine; in this regard,
     DPUI shall diligently and promptly review all drafts of such Alleghany
     Public Filings as are requested by Alleghany and shall prepare in a
     diligent and timely fashion any portion of such Alleghany Public Filing
     pertaining to DPUI or its Subsidiaries requested by Alleghany;

          (iii) to provide to Alleghany in connection with each quarterly and
     annual report filed by Alleghany with the SEC, reasonably in advance of the
     Alleghany Audit Committee related to such filing, the certifications from
     each of the CEO and the CFO of DPUI pursuant to Section 302 of the
     Sarbanes-Oxley Act (the "DPUI Certifications"); provided, however, that if
     the DPUI Certifications are not available reasonably in advance of such
     Alleghany Audit


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     Committee meeting, the CEO and CFO shall sign certifications which support
     the certifications made by the CEO and the CFO of Alleghany in connection
     with such filing pursuant to Section 302 of the Sarbanes-Oxley Act of 2002,
     and such certification by the CEO and the CFO of DPUI shall be in such form
     as Alleghany then requires from its other Subsidiaries;

          (iv) to provide to Alleghany, reasonably in advance of the Alleghany
     Audit Committee meeting relating to the Annual Report on Form 10-K filed by
     Alleghany with the SEC, a DPUI management report, including an annual
     assessment by DPUI management of DPUI's internal control over financial
     reporting; provided, however, that if such DPUI management report is not
     available reasonably in advance of such Alleghany Audit Committee meeting,
     DPUI shall prepare and execute a management report in such form as
     Alleghany then requires from its other Subsidiaries;

          (v) that, without prior notice to Alleghany, DPUI shall not publicly
     release any financial or other information which conflicts with the
     information with respect to DPUI, any Affiliate of DPUI or the DPUI Group
     that is provided by DPUI for any Alleghany Public Filing;

          (vi) to use its best efforts to enable the DPUI Auditors to complete
     their audit such that they will date their opinion on DPUI's audited annual
     financial statements on the same date (or prior to the date) that the
     Alleghany Auditors date their opinion on the Alleghany Annual Statements,
     and to enable Alleghany to meet its timetable for the printing, filing and
     public dissemination of the Alleghany Annual Statements; and

          (vii) to provide such other information, certifications, reports or
     cooperation as the other Subsidiaries of Alleghany are from time to time
     required to provide to Alleghany.

          (e) DPUI Public Information and SEC Reports. DPUI shall file its
Quarterly Reports on Form 10-Q and its Annual Reports on Form 10-K with the SEC
as soon as possible (and in no event later than one Business Day) following
Alleghany's filing of its quarterly and annual reports with the SEC for the
corresponding period. In no event shall DPUI file any Quarterly Report on Form
10-Q or Annual Report on Form 10-K with the SEC prior to the time that Alleghany
files its corresponding report on Form 10-Q or Form 10-K with the SEC; provided,
however that such restriction shall not apply to the extent that compliance with
such restriction would cause DPUI not to be in compliance with its SEC filing.
DPUI shall deliver to Alleghany (to the attention of its General Counsel), no
later than the date the same are printed for distribution to its stockholders,
sent to its stockholders or filed with the SEC, whichever is earliest, final
copies of all DPUI reports, notices and proxy and information statements to be
sent or made available by DPUI or such Subsidiaries to their security holders,
all regular, periodic and other reports filed under Sections 13, 14 and 15 of
the Exchange Act by DPUI or such Subsidiaries and all registration statements
and prospectuses to be filed by DPUI or such Subsidiaries with the SEC or any
securities exchange pursuant to the listed


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company manual (or similar requirements) of such exchange (collectively, "DPUI
Public Documents"). Alleghany shall have the right to review, reasonably in
advance of public release or filing or release to financial analysts or
investors (i) all press releases and other statements to be made available by
DPUI or any of its Subsidiaries to the public which contain DPUI financial
information, results of operation, earnings guidance or information with respect
to transactions or matters outside the ordinary course of DPUI's business, (ii)
all reports and other information prepared by DPUI or any of its Subsidiaries
for release to financial analysts or investors which contain DPUI financial
information, results of operation, earnings guidance with respect to
transactions or information matters outside the ordinary course of DPUI's
business, and (iii) all DPUI Public Documents.

          (f) Earnings Releases. DPUI agrees that unless Alleghany shall have
consented thereto, no member of the DPUI Group will publicly release any
quarterly, annual or other financial information of DPUI or any of its
Subsidiaries ("DPUI Information") prior to the time that Alleghany publicly
releases financial information of Alleghany for the relevant period. DPUI shall
publicly release its financial results for each annual and quarterly period
immediately (and in no event later than one Business Day) following Alleghany's
release of its financial results for the corresponding period.

          (g) Other Financial Information. DPUI shall provide to Alleghany upon
request such other financial information and analyses of DPUI and its
Subsidiaries that may from time to time be requested by Alleghany, including
without limitation such information as may be required to enable Alleghany to
comply with applicable financial reporting requirements or its customary
financial reporting practices.

          (h) Annual Reports Furnished to State Insurance Regulatory
Authorities. Promptly following the filing by DPUI or any Subsidiary of DPUI of
annual reports with any state insurance regulatory authority in each
jurisdiction in which such reports are required to be filed, DPUI shall deliver
the final forms of such reports to Alleghany.

          (i) Meetings with Financial Analysts. DPUI shall notify Alleghany
reasonably in advance of the date of all scheduled meetings and conference calls
to be held between DPUI and members of the investment community (including any
financial analysts), and of any conferences to be attended by management of DPUI
with members of the investment community, and shall consult with Alleghany as to
the appropriate timing for all such scheduled meetings, calls and conferences.
With respect to any such meeting, call or conference, DPUI shall not schedule
such meeting or call or attend such conference on any date to which Alleghany
objects.

          (j) Communications with Regulators. DPUI shall notify Alleghany
promptly of any communications that DPUI or any member of the DPUI Group may
have or receive from time to time with or from any regulators, including the
SEC, any self-regulatory organization with appropriate jurisdiction, NYSE Arca
and any state insurance regulators, in connection with any compliance,
regulatory or accounting matters; provided that DPUI shall not be required to
provide notification of routine


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communications with or from state insurance regulators in the ordinary course of
business. Without limitation of the foregoing, DPUI shall promptly provide
Alleghany with copies of any written correspondence with regulators, provided
that DPUI shall not be required to provide copies of routine correspondence with
state insurance regulators in the ordinary course of business.

          2.2 Internal Control / Audit. DPUI agrees that if Alleghany is
required during or for any fiscal year, in accordance with GAAP, to account for
its investment in DPUI on a consolidated basis or under the equity method of
accounting, then, unless stated otherwise herein, in respect of such fiscal
year:

          (a) Maintenance of Books and Records. DPUI shall, and shall cause each
of its consolidated Subsidiaries to, (i) make and keep books, records and
accounts, which, in reasonable detail, accurately and fairly reflect the
transactions and dispositions of the assets of DPUI and such Subsidiaries and
(ii) devise and maintain a system of internal accounting controls sufficient to
provide reasonable assurances that: (A) transactions are executed in accordance
with management's general or specific authorization; (B) transactions are
recorded as necessary to permit preparation of financial statements in
conformity with GAAP and to maintain accountability for assets; (C) access to
assets is permitted only in accordance with management's general or specific
authorization; and (D) the recorded accountability for assets is compared with
the existing assets at reasonable intervals and appropriate action is taken with
respect to any differences.

          (b) Access to Company Records and Personnel. DPUI shall provide the
Alleghany Representatives and the Alleghany Auditors with full access to DPUI's
books and records and to the internal accounting controls and operations of
DPUI. DPUI shall also provide the Alleghany Representatives and the Alleghany
Auditors with full access to the officers, directors and employees of DPUI and
the other members of the DPUI Group and to the DPUI Auditors so that the
Alleghany Representatives and the Alleghany Auditors may discuss with them the
affairs, finances, accounts and prospects relating to DPUI and the other members
of the DPUI Group.

          (c) Access to Personnel and Working Papers. DPUI will request the DPUI
Auditors to make available to the Alleghany Auditors both the personnel who
performed or are performing the annual audit of DPUI and, consistent with
customary professional practice and courtesy of such auditors with respect to
the furnishing of work papers, work papers related to the annual audit of DPUI,
in all cases on a time frame that will enable the Alleghany Auditors to perform
the procedures they consider necessary to take responsibility for the work of
the DPUI Auditors as it relates to the Alleghany Auditors' report on the
Alleghany Annual Statements, all within sufficient time to enable Alleghany to
meet its timetable for the printing, filing and public dissemination of the
Alleghany Annual Statements.

          (d) Accounting Estimates and Principles. DPUI will give Alleghany
notice of any proposed material change in accounting estimates or material
change in accounting principle (including without limitation changes in
reserving practices) from


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<PAGE>

those currently in effect at DPUI and its Subsidiaries. DPUI will consult with
Alleghany with respect to any such proposed change and, if requested by
Alleghany, DPUI will, and will cause the DPUI Auditors to, consult with the
Alleghany Auditors with respect thereto. Without limitation of the foregoing, if
Alleghany so requests, DPUI will be required to obtain the concurrence of the
DPUI Auditors as to such material change prior to its implementation. For so
long as Alleghany is required during or for any fiscal year, in accordance with
GAAP, to account for its investment in DPUI on a consolidated basis, DPUI agrees
that it will not implement any such proposed material change in accounting
estimates or accounting principle without Alleghany's prior written consent
(excluding changes that, in the opinion of the DPUI Auditors, are mandated or
required by the SEC, the Financial Accounting Standards Board or the Public
Company Accounting Oversight Board).

          (e) Reports of Accountants and External Actuaries. Promptly, but in no
event later than five Business Days following the receipt thereof, DPUI shall
deliver to Alleghany copies of (i) all reports submitted to DPUI or any of its
Subsidiaries by the DPUI Auditors, including, without limitation, each report
submitted to DPUI or any of its Subsidiaries concerning its accounting practices
and systems and any comment letter submitted to management in connection with
the annual audit conducted by the DPUI Auditors and all responses by management
to such reports and letters and (ii) all reports and opinions submitted to DPUI
or any of its Subsidiaries by their external actuaries.

          (f) Alleghany Audit Committee Approval. To the extent required by
statute, SEC rules and regulations, any self-regulatory organization with
appropriate jurisdiction (including, without limitation, the NYSE exchange or
any other stock exchange on which the shares of Alleghany common Stock are
listed), or any state insurance regulators law, all engagements of the DPUI
Auditors, whether for audit services or for non-audit services, must be approved
by the Alleghany Audit Committee.

          2.3 Board Meetings. DPUI agrees that, for so long as Alleghany is
required during or for any fiscal year, in accordance with GAAP, to account for
its investment in DPUI on a consolidated basis or under the equity method of
accounting, then in respect of such fiscal year, at the request of Alleghany,
the executive officers of DPUI shall make themselves available to attend
meetings of the Alleghany Board and shall provide such reports to the Alleghany
Board as Alleghany shall request.

          2.4 Corporate Compliance Program. DPUI agrees, for so long as
Alleghany is required during or for any fiscal year, in accordance with GAAP, to
account for its investment in DPUI on a consolidated basis or under the equity
method of accounting, (i) to maintain a corporate compliance program which
meets, in all material respects, the elements of an "effective" corporate
compliance program as defined by the U.S. Sentencing Guidelines for
Organizations, (ii) at all times to have a Chief Compliance Officer who shall
provide regular reports to the DPUI Audit Committee and to the Alleghany Chief
Compliance Officer (the "Alleghany CCO"), (iii) at the request of the Alleghany
CCO, to furnish compliance information related to DPUI and to the members of the
DPUI Group, in such form and detail as may be requested by the Alleghany CCO,
(iv) to provide the Alleghany CCO with advance notice of any proposed


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change in DPUI's Code of Conduct or of any other material change proposed to
other elements of its compliance program and (v) to provide notice to the
Alleghany CCO of any material violation by a director, officer or employee of
DPUI or other member of the DPUI Group of its Code of Conduct or other
provisions of DPUI's compliance program.

                                   ARTICLE III

                                 CERTAIN MATTERS

          3.1 Amended and Restated Certificate of Incorporation and Amended and
Restated Bylaws. Prior to the Effective Time, each of DPUI and Alleghany shall
take all necessary action that may be required to provide for the adoption by
DPUI of the Amended and Restated Certificate of Incorporation of DPUI in the
form attached hereto as Exhibit __ (the "Charter"), and the Amended and Restated
Bylaws of DPUI in the form attached hereto as Exhibit __ (the "Bylaws"), in each
case, with such changes thereto as may be approved by Alleghany.

          3.2 The Initial Public Offering. At the direction of Alleghany, DPUI
shall execute and deliver the Purchase Agreement in such form and substance as
is reasonably satisfactory to Alleghany, and DPUI shall promptly take any and
all actions as may be directed by Alleghany in connection with the consummation
of the Initial Public Offering as contemplated by the IPO Registration Statement
and the Purchase Agreement.

          3.3 Covenant Not to Take Certain Actions Affecting Alleghany. DPUI
hereby covenants and agrees that it shall not, without the prior written consent
of Alleghany (which Alleghany may withhold in its sole and absolute discretion)
take, or cause to be taken, directly or indirectly, any action which has the
effect, directly or indirectly, of restricting or limiting the ability of
Alleghany or any member of the Alleghany Group to freely sell, transfer, assign,
pledge or otherwise dispose of shares of Common Stock. Without limiting the
generality of the foregoing, DPUI shall not, without the prior written consent
of Alleghany (which Allegany may withhold in its sole and absolute discretion),
take any action, or recommend to its stockholders any action, which would limit
the legal rights of, or deny any benefit to, Alleghany or any member of the
Alleghany Group as a stockholder of DPUI in a manner not applicable to
stockholders of DPUI generally.

          3.4 Adoption of Stockholder Rights Plan. DPUI agrees that for so long
as members of the Alleghany Group beneficially own, in the aggregate, ten
percent (10%) or more of the then outstanding shares of Common Stock, DPUI shall
not adopt or implement any stockholder rights plan or similar takeover defense
measure without Alleghany's prior written consent.

          3.5 Dilutive Issuances. DPUI agrees that for so long as members of the
Alleghany Group beneficially own, in the aggregate, more than fifty percent
(50%) of the then outstanding shares of Common Stock, DPUI shall not issue any
shares of Common Stock or any securities convertible into or exercisable or
exchangeable for


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shares of Common Stock (including, without limitation, options and warrants) or
any other rights to acquire shares of Common Stock or any such securities, or
take any other action, the effect of which would be to reduce Alleghany's
beneficial ownership of Common Stock to less than fifty percent (50%) of the
then outstanding shares of Common Stock.

          3.6 Repurchase of Common Stock. DPUI agrees that for so long as
members of the Alleghany Group beneficially own, in the aggregate, more than
fifty percent (50%) of the then outstanding shares of Common Stock, DPUI shall
not, and shall cause the other members of the DPUI Group not to, purchase,
redeem or otherwise acquire or retire for value any shares of Common Stock or
any warrants, options or other rights to acquire Common Stock other than (i) the
repurchase of Common Stock deemed to occur upon exercise of stock options to the
extent that shares of Common Stock represent a portion of the exercise price of
the stock options or are withheld by DPUI to pay applicable withholding taxes
and (ii) the repurchase of Common Stock deemed to occur to the extent shares of
Common Stock are withheld by DPUI to pay applicable withholding taxes in
connection with any grant or vesting of restricted stock.

                                   ARTICLE IV

                                OTHER AGREEMENTS

          4.1 Further Assurances. In addition to the actions specifically
provided for elsewhere in this Agreement, each of the parties hereto will
cooperate with each other and use (and will cause their respective Subsidiaries
and Affiliates to use) commercially reasonable efforts, prior to, on and after
the Closing Date, to take, or to cause to be taken, all actions, and to do, or
to cause to be done, all things reasonably necessary on its part under
applicable Law or contractual obligations to consummate and make effective the
transactions contemplated by this Agreement.

          4.2 Insurance Matters.

          (a) Alleghany and DPUI acknowledge that, immediately following
completion of the Initial Public Offering, members of the DPUI Group will
continue to be covered under the umbrella insurance policies and the director
and officer liability insurance policies maintained by Alleghany for the benefit
of Alleghany and its Subsidiaries (the "Alleghany Policies"). DPUI agrees that
for so long as coverage under the Alleghany Policies is continued, members of
the DPUI Group will pay to Alleghany amounts representing their allocable
portions of the premiums for such Alleghany Policies as determined by Alleghany.
DPUI agrees that Alleghany may terminate the coverage of the members of the DPUI
Group under any of the Alleghany Policies at any time upon at least 60 days'
written notice to DPUI and that, upon receipt of such notice, it will be the
responsibility of DPUI to obtain, at its own expense, replacement umbrella
insurance and/or directors and officers liability insurance coverage.

          (b) DPUI may terminate coverage of members of the DPUI Group under the
Alleghany Policies at any time; provided that the termination by DPUI of


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coverage of the members of the DPUI Group under any Alleghany Policy shall not
relieve the members of the DPUI Group to pay to Alleghany, through the current
expiration date of such Alleghany Policy as of the time of termination of
coverage of members of the DPUI Group thereunder by DPUI, amounts representing
their allocable portions of the premiums under such Alleghany Policy as
determined by Alleghany.

          (c) In no event shall Alleghany or any other member of the Alleghany
Group have any liability or obligation whatsoever to any member of the DPUI
Group, or to any director or officer of any member of the DPUI Group, if any of
the Alleghany Policies shall be terminated or otherwise cease to be in effect or
for any reason shall be unavailable or inadequate to cover any liability of any
member of the DPUI Group or of any director or officer of any member of the DPUI
Group.

          (d) DPUI agrees, on behalf of itself and each Subsidiary of DPUI, that
any claim asserted by DPUI or any Subsidiary of DPUI under any of the Alleghany
Policies may be asserted only through Alleghany.

          4.3 Indemnification. DPUI and Alleghany agree that it shall be the
responsibility of DPUI, and not the responsibility of Alleghany, to indemnify
any director or officer of a member of the DPUI Group who asserts a claim for
indemnification arising from his or her service as a director or officer of a
member of the DPUI Group, regardless of whether such claim arises from an event
occurring prior or subsequent to the completion of the Initial Public Offering.
DPUI further agrees that it shall indemnify Alleghany and hold Alleghany
harmless against any loss, liability or expense arising from the assertion of
any such claim against Alleghany.

          4.4 Investment Management. DPUI and Alleghany agree that, subsequent
to the completion of the Initial Public Offering, Alleghany will have no
obligation to provide investment management services or investment advice to
members of the DPUI Group. DPUI acknowledges and agrees that Alleghany has no
obligation to provide to members of the DPUI Group investment ideas or
opportunities to share in investments made by Alleghany or made available by
Alleghany to other members of the Alleghany Group.

          4.5 Allocation of Costs and Expenses.

DPUI agrees, for so long as Alleghany is required during or for any fiscal year,
in accordance with GAAP, to account for its investment in DPUI on a consolidated
basis or under the equity method of accounting, Alleghany may, with reasonable
notice to and the consent of DPUI (such consent not to be unreasonably
withheld), retain third parties for the benefit of DPUI or any other member of
the DPUI Group. DPUI shall pay the fees and expenses of the third party (or to
the extent paid for by Alleghany, will promptly reimburse Alleghany for any and
all amounts so paid), including without limitation the fees and expenses of KPMG
LLP. To the extent that such fees are charged by a third party on a basis that
relates to members of the Alleghany Group and members of the DPUI Group, then
DPUI shall be responsible for payment (or reimbursement) of the



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<PAGE>

portion of such fees and expenses charged by such third party as are reasonably
allocable to members of the DPUI Group.

          4.6 Charter Provision. DPUI shall, and shall cause each of its
Subsidiaries to, take any and all actions necessary to ensure continued
compliance by DPUI and its Subsidiaries with the provisions of its certificate
or articles of incorporation and by-laws. DPUI shall notify Alleghany in writing
promptly after becoming aware of any act or activity taken or proposed to be
taken by DPUI or any of its Subsidiaries which resulted or would result in
non-compliance with any such charter provisions. DPUI and its Subsidiaries shall
take or refrain from taking all actions necessary or desirable to prevent or
remedy any non-compliance with the provisions of its certificate or articles of
incorporation and by-laws.

          4.7 Alleghany Policies. Except as otherwise agreed by Alleghany or
unless superseded by any comparable policies adopted by the Darwin Board, the
policies of Alleghany that apply to Subsidiaries of Alleghany shall apply to
DPUI and its Subsidiaries for so long as members of the Alleghany Group
beneficially own, in the aggregate, more than fifty percent (50%) of the then
outstanding shares of Common Stock. The key policies of Alleghany applicable to
DPUI and its Subsidiaries as of the Closing Date are listed on Schedule 4.7.

                                    ARTICLE V

                                  MISCELLANEOUS

          5.1 Governing Law; Consent to Jurisdiction; Waiver of Jury Trial. This
Agreement shall be governed by and construed in accordance with the laws of the
State of Delaware, regardless of the laws that might otherwise govern under
applicable principles of conflicts of laws thereof. Each of the parties hereby
irrevocably and unconditionally consents to submit to the exclusive jurisdiction
of the courts of the state and federal courts located in the State of Delaware
for the purposes of enforcing this Agreement. The parties shall take such
actions as are within their control to cause any matter contemplated hereby to
be assigned to the Chancery Court of the State of Delaware. In any action, suit
or other proceeding, each of the parties hereto irrevocably and unconditionally
waives and agrees not to assert by way of motion, as a defense or otherwise any
claim that it is not subject to the jurisdiction of the above courts, that such
action or suit is brought in an inconvenient forum or that the venue of such
action, suit or other proceeding is improper. Each of the parties hereto also
agrees that any final and unappealable judgment against a party hereto in
connection with any action, suit or other proceeding shall be conclusive and
binding on such party and that such award or judgment may be enforced in any
court of competent jurisdiction, either within or outside of the United States.
A certified or exemplified copy of such award or judgment shall be conclusive
evidence of the fact and amount of such award or judgment. Each of the parties
hereto hereby irrevocably waives any and all right to trial by jury in any legal


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proceeding arising out of or related to this Agreement or the transactions
contemplated hereby.

          5.2 Survival of Covenants. The covenants and other agreements
contained in this Agreement, and liability for the breach of any obligations
contained herein, shall survive the Initial Public Offering and shall remain in
full force and effect.

          5.3 Notices. All notices, requests and other communications pursuant
to this Agreement shall be in writing and shall be deemed to have been duly
given, if delivered in person or by courier, or sent by express, registered or
certified mail, postage prepaid, to the Alleghany Group or to the DPUI Group at
the address set forth below:

          If to the Alleghany Group, to:

               Alleghany Insurance Holdings LLC
               c/o Alleghany Corporation
               7 Times Square Tower
               17th Floor
               New York, NY 10036
               Attention: Chairman

               with a copy to:

               Alleghany Corporation
               7 Times Square Tower
               17th Floor
               New York, NY 10036
               Attention: General Counsel

          If to the DPUI Group, to:

               Darwin Professional Underwriters, Inc.
               9 Farm Springs Road
               Farmington, Connecticut 06032
               Attention: Chairman

               with a copy to:

               Darwin Professional Underwriters, Inc.
               9 Farm Springs Road
               Farmington, Connecticut 06032
               Attention: General Counsel

          5.4 Severability. If any term or other provision of this Agreement is
invalid, illegal or incapable of being enforced under any Law or as a matter of
public policy, all other conditions and provisions of this Agreement shall
nevertheless remain in full force and effect. Upon such determination that any
term or other provision is invalid, illegal or incapable of being enforced, the
parties to this Agreement shall negotiate in


                                       14

<PAGE>

good faith to modify this Agreement so as to effect the original intent of the
parties as closely as possible in a mutually acceptable manner in order that the
transactions contemplated by this Agreement be consummated as originally
contemplated to the greatest extent possible.

          5.5 Entire Agreement. Except as otherwise expressly provided in this
Agreement, this Agreement (including the Schedules and Exhibits hereto)
constitutes the entire agreement of the parties hereto with respect to the
subject matter of this Agreement and supersedes all prior agreements and
undertakings, both written and oral, between or on behalf of the parties hereto
with respect to the subject matter of this Agreement. For the avoidance of
doubt, nothing in this Agreement shall be deemed to supersede or to amend in any
respect any of the Registration Rights Agreement, the Tax Sharing Agreement, or
any other agreement currently in effect between any member of the Alleghany
Group, on the one hand, and any member of the DPUI Group, on the other hand,
including without limitation the agreements between members of the DPUI Group
and the Capitol Companies, which have been filed as exhibits to the IPO
Registration Statement (collectively, the "Intercompany Agreements"), and each
of the Intercompany Agreements shall remain in full force and effect in
accordance with its respective terms as such terms may be modified from time to
time as permitted under the terms of such Intercompany Agreement.

          5.6 Amendment. No provision of this Agreement may be amended or
modified except by a written instrument signed by all the parties hereto. No
waiver by any party of any provision hereof shall be effective unless explicitly
set forth in writing and executed by the party so waiving. The waiver by any
party hereto of a breach of any provision of this Agreement shall not operate or
be construed as a waiver of any other subsequent breach.

          5.7 Rules of Construction. Interpretation of this Agreement shall be
governed by the following rules of construction: (a) words in the singular shall
be held to include the plural and vice versa, and words of one gender shall be
held to include the other gender, in each case as the context requires, (b)
references to the terms Article, Section, paragraph, Schedule and Exhibit are
references to the Articles, Sections, paragraphs, Schedules and Exhibits to this
Agreement unless otherwise specified, (c) the word "including" and words of
similar import shall mean "including, without limitation," (d) provisions shall
apply, when appropriate, to successive events and transactions, (e) the table of
contents and headings contained herein are for reference purposes only and shall
not affect in any way the meaning or interpretation of this Agreement and (f)
this Agreement shall be construed without regard to any presumption or rule
requiring construction or interpretation against the party drafting or causing
any instrument to be drafted.

          5.8 Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.


                                       15

<PAGE>

          5.9 Specific Performance. The parties hereto acknowledge that there
would be no adequate remedy at law if any party fails to perform any of its
obligations hereunder, and accordingly agree that each party, in addition to any
other remedy to which it may be entitled at law or in equity, shall be entitled
to injunctive relief, including specific performance, to enforce such
obligations without the posting of any bond, and, if any action should be
brought in equity to enforce any of the provisions of this Agreement, none of
the parties hereto shall raise the defense that there is an adequate remedy at
law.

          5.10 Further Assurances. Each party hereto shall do and perform or
cause to be done and performed all such further acts and things and shall
execute and deliver all such other agreements, certificates, instruments, and
documents as any other party hereto reasonably may request in order to carry out
the intent and accomplish the purposes of this Agreement and the consummation of
the transactions contemplated hereby.

            [The remainder of this page is intentionally left blank]


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

                                        ALLEGHANY CORPORATION


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------


                                        DARWIN PROFESSIONAL UNDERWRITERS, INC.


                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------