Exhibit 10.1

Aspen Insurance Limited
Attn Bryan Astwood
Group Treasurer
Maxwell Roberts Building
1 Church Street
Hamilton
HM 11
Bermuda

October 11, 2006

Dear Bryan,

Committed letter of credit facility

Further to recent discussions, Citibank Europe plc (‘‘the Bank’’) is pleased to
confirm its committed letter of credit issuance facility (‘‘the Facility’’)
subject to the terms and conditions set out in this Letter.

Amount

The Facility shall be in a maximum aggregate amount of US$300,000,000 (‘‘the
Facility Limit’’).

Facility Documents

Aspen Insurance Limited (‘‘the Company’’) have entered into the following
documents in relation to the Facility:

[spacer.gif] [spacer.gif] (a)  Insurance Letters of Credit - Master Agreement
(Form 3/CIFS) dated 15 December 2003 (the ‘‘Master Agreement’’);

[spacer.gif] [spacer.gif] (b)  Reinsurance Deposit Agreement (Charge Form –
Citibank N.A. as Custodian) dated 15 December 2003 (‘‘Form 12’’);

[spacer.gif] [spacer.gif] (c)  Pledge Agreement dated 17 January 2006 (‘‘the
Pledge Agreement’’);

[spacer.gif] [spacer.gif] (d)  Collateral Account Control Agreement dated 17
January 2006 (‘‘the Collateral Account Control Agreement’’) and

[spacer.gif] [spacer.gif] (e)  Corporate Mandate dated 10 December 2003.

In the event of any inconsistency between the terms of this letter and the terms
of any Facility Document, the terms of this letter shall prevail.

Conditions precedent

The Company shall not request the issue of any Credit until the Bank has
received the documents and other evidence specified below in a form and
substance satisfactory to the Bank (each a ‘‘Condition Precedent’’), items (a)
to (c) to be received by the Bank on or before 18 October 2006:

[spacer.gif] [spacer.gif] (a)  the enclosed duplicate of this Letter, duly
executed on behalf of the Company;

[spacer.gif] [spacer.gif] (b)  the Assignment Agreement duly executed by the
Company whereunder all the rights and obligations of Citibank N.A. under the
Pledge Agreement shall be assumed by the Bank in accordance with the terms of
such Assignment Agreement;

Citibank Ireland Financial Services plc
Directors: Aidan M Brady, Maurice F Doyle, Mark Fitzgerald, Mark Fulton
(U.K./Australia),
Adrian Gray (U.K.), Brian Hayes, Peter Maskrey (U.K.), Frank McCabe, Daniel Nagy
(U.S.A.), Francesco Vanni d'Archirafi (Italy)
Registered in Ireland: Registration Number 132781. Registered Office: 1 North
Wall Quay, Dublin 1,
Ultimately owned by Citigroup Inc., New York, U.S.A.

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[spacer.gif] [spacer.gif] (c)  the amendment letter duly executed by the Company
whereunder the parties agree to certain amendments to the Form 12 and the Pledge
Agreement; and

[spacer.gif] [spacer.gif] (d)  such other documents and other evidence as the
Bank may reasonably require from time to time.

Utilisation requests

The Bank shall be entitled to examine each request to issue a Credit on a
case-by-case basis and, notwithstanding clause 1(a)(i) of the Master Agreement,
during the continuance of this Letter, shall only be entitled to decline any
such request without liability where:

[spacer.gif] [spacer.gif] (a)  such request would cause the Bank to be in breach
of any law of any jurisdiction (including non-exclusively any breach of
sanctions imposed by the law of the United States of America); or

[spacer.gif] [spacer.gif] (b)  the Credit requested is in a currency other than
US dollars, GB pounds sterling, Canadian dollars or Euros; or

[spacer.gif] [spacer.gif] (c)  any deposit(s) as may have been requested by the
Bank to be placed in the accounts established pursuant to the terms of the Form
12 and/or Pledge and Collateral Account Control Agreements have not been carried
out to the Bank's satisfaction.

Fees

The Company shall pay to the Bank in advance on the date of this Letter and on
each Quarter Day a letter of credit fee in an amount equal to (a) 0.2% (on an
annualised basis) in respect of the amount of credit drawn, where such amount is
secured by collateral under Tranche 1 of Schedule 1 of the Pledge Agreement (as
amended) (‘‘Tranche 1 Financial Assets’’); and/or (b) 0.25% (on an annualised
basis) in respect of the amount of credit drawn, where such amount is secured by
collateral under Tranche 2 of Schedule 1 of the Pledge Agreement (as amended)
(‘‘Tranche 2 Financial Assets’’) and each within the Facility Limit and the
terms of Schedule 1 of the Pledge Agreement. The fee payable on the date of this
Letter shall be pro-rated for the number of days until 1 October 2006.

The Company shall pay to the Bank on the date of this Letter and on each Quarter
Day a commitment fee in an amount equal to (a) 0.075% (on an annualised basis)
of US$150,000,000 less the principal amount of drawn credit secured with Tranche
1 Financial Assets on that Quarter Day and (b) 0.1% (on an annualised basis) of
US$150,000,000 less the principal amount of drawn credit secured with Tranche 2
Financial Assets on that Quarter Day.

Repayment and expiry

The Facility shall apply in respect of Credits issued prior to 11 October 2006
and Credits to be issued on or after 11 October 2006. The Facility shall expire
on 10 October 2009 and the Bank and the Company shall commence negotiations,
without being under any obligation, on the renewal of the Facility at least 60
days before such date.

Without prejudice to the continuing application of this Letter and the other
Facility Documents in respect of issued Credits, the Bank may at any time
terminate the Facility by notice in writing to the Company.

Representations and warranties

The Company represents and warrants to the Bank on the date of its acceptance of
this Letter and, with reference to (ii) below only, on each day (by reference to
the facts and circumstances then existing) until this Letter has expired or
terminated, that there is no pending or, to the knowledge of the Company,
threatened action, suit, investigation, litigation or proceeding affecting any
member of the Group before any court, governmental agency or arbitrator that (i)
could be reasonably likely to have a material adverse effect on the financial
position or prospects of the Group or (ii) purports to affect the legality,
validity or enforceability of this Letter or any Facility Document or the
consummation of the transactions contemplated hereby.

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The Company repeats the representations, warranties and undertakings laid out in
clauses 1(f) and (g) of the Master Agreement in favour of the Bank in relation
to this Letter as if they were more fully laid out herein, with the necessary
changes, on the date of acceptance of this Letter and on each day (by reference
to the facts and circumstances then existing) until this Letter has expired or
terminated.

Undertakings

The Company agrees with the Bank, that in the event that the Company's A.M. Best
Rating should at any time drop from its current level to a rating of BBB- or
below, that this will entitle the Bank to require the Company on 90 days notice,
to transfer the Collateral from the Account to an account at Citibank N.A.
London, England branch (‘‘CNA-LON’’) and to execute a replacement deposit
agreement (in substantially the customary form used by CNA-LON and a copy of
which deposit agreement has been provided to the Company) in substitution for
the Pledge Agreement and Collateral Account Control Agreement (the terms
‘‘Collateral’’ and ‘‘Account’’ where used in this paragraph are as defined in
the Pledge Agreement).

Costs and expenses

The Company undertakes to indemnify the Bank, on demand, for and against all
actions, proceedings, losses, damages, charges, costs, expenses, claims and
demands which you may incur, pay or sustain (apart from the Bank's own gross
negligence or wilful misconduct) in connection with this Letter (including
non-exclusively the cost of all registrations and any other legal fees that the
Bank incurs in relation to the Facility).

Certificates

Any demand, notification or certificate issued by the Bank specifying any amount
due under this Letter or any Facility Document or any determination of any ratio
shall, in the absence of manifest error, be conclusive and binding on the
Company.

Miscellaneous

The rights of the Bank under this Letter and the Facility Documents may be
exercised as often as necessary; are cumulative and not exclusive of its rights
under the general law; and may be waived only in writing and specifically. Delay
in exercising or non-exercise of any such right is not a waiver of that right.

If any provision of this Letter or any Facility Document is or becomes illegal,
invalid or unenforceable in any jurisdiction, that shall not affect (i) the
legality, validity or enforceability in that jurisdiction of any other provision
of that document; or (ii) the legality, validity or enforceability in any other
jurisdiction of that or any other provision of that document.

In no event shall the Bank be liable on any theory of liability for any special,
indirect, consequential or punitive damages and the Company hereby waives,
releases and agrees (for itself and on behalf of the other members of the Group)
not to sue upon any such claim for any such damages, whether or not accrued and
whether or not known or suspected to exist in its or their favour.

Clauses 12, 13 and 14 of the Master Agreement, Section 17 of the Pledge
Agreement and Article V, Section 3 of the Collateral Account Control Agreement
shall apply in respect of this Letter, with necessary changes.

The terms of this Letter may not be waived, modified or amended unless such
waiver, modification or amendment is in writing and signed by your nor may the
Company assign any of its rights hereunder without the prior written consent of
the Bank.

Definitions and interpretation

Terms defined in any Facility Document shall have the same meanings when used in
this Letter. Additionally, the following terms have the following meanings.

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A. M. Best Rating means a claims paying rating from A. M. Best Co. (or any
successor), provided that if such rating system shall change, or if it (or its
successors) shall cease to be in the business of rating the financial strength
of insurance companies like the Company, the Company shall negotiate in good
faith to amend the references to specific A. M. Best Co. ratings in this Letter
to reflect such changed rating system or the non-availability of ratings from
such rating agency (provided that no such amendments shall be effective unless
approved by the Bank).

Business Day means a day (other than a Saturday or a Sunday) on which banks are
generally open in Dublin and Bermuda.

Facility Documents means the documents as specified in the paragraph of this
Letter headed ‘‘Facility Documents’’ and any other document pursuant to which a
security interest, guarantee or other form of credit support is created or
exists in favour of the Bank in respect of the obligations of the Company under
this Letter.

Group means the Company and each other person, if any, from time to time
included in the consolidated financial statements of the Company filed with the
SEC.

Quarter Day means 1 January, 1 April, 1 July and 1 October.

In this Letter (unless otherwise provided):

[spacer.gif] [spacer.gif] (a)  words importing the singular shall include the
plural and vice versa;

references to:

[spacer.gif] [spacer.gif] (i)  paragraphs are to be construed as references to
the paragraphs of this Letter;

[spacer.gif] [spacer.gif] (ii)  any document shall be construed as references to
that document, as amended, varied, novated or supplemented;

[spacer.gif] [spacer.gif] (iii)  any statute or statutory provision shall
include any statute or statutory provision which amends, extends, consolidates
or replaces the same;

[spacer.gif] [spacer.gif] (iv)  any document or person being acceptable or
approved or satisfactory shall be construed as meaning acceptable to or approved
by or satisfactory to the Bank in its sole discretion;

[spacer.gif] [spacer.gif] (v)  a person shall be construed so as to include that
person's assignors, transferees or successors in title and shall be construed as
including references to an individual, firm, partnership, joint venture,
company, corporation, body corporate, unincorporated body of persons or any
state or any agency of a state; and

[spacer.gif] [spacer.gif] (vi)  time are to Dublin time.

The headings in this Letter are for convenience only and shall be ignored in
construing this Letter.

Governing law

This Letter shall be governed by English law and for the benefit of the Bank the
Company irrevocably submit to the jurisdiction of the English Courts in respect
of any dispute which may arise from or in connection with this Letter or any
Credit.

A person who is not a party to this Letter has no rights under the Contracts
(Rights of Third Parties) Act 1999 to enforce any terms of this Letter.

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Yours sincerely

    
/s/ Phil Arch    

[spacer.gif] [spacer.gif][spacer.gif] [spacer.gif] [spacer.gif]

For and on behalf of Citibank Europe plc

    

Accepted and agreed on 11 October 2006

    
/s/ David Skinner

[spacer.gif] [spacer.gif][spacer.gif] [spacer.gif] [spacer.gif]

Aspen Insurance Limited

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