Exhibit 5.1



SIDLEY AUSTIN     SIDLEY AUSTIN (UK) LLP   |BEIJING   GENEVA      SAN FRANCISCO
- ----------------| WOOLGATE EXCHANGE        |BRUSSELS  HONG KONG   SHANGHAI
SIDLEY          | 25 BASINGHALL STREET     |CHICAGO   LONDON      SINGAPORE
                  LONDON EC2V 5HA          |DALLAS    LOS ANGELES TOKYO
                  DX NUMBER 580 LONDON CITY|FRANKFURT NEW YORK    WASHINGTON, DC
                  +44 (0) 20 7360 3600     |
                  +44 (0) 20 7626 7937 FAX |
                                           |
                                           |
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Granite Master Issuer plc
Fifth Floor
100 Wood Street
London
EC2V 7EX



                                                                  March 28, 2007



Dear Sirs


                      Registration Statement on Form S-3

1.    INTRODUCTION

1.1   We have acted as English legal advisers to Granite Master Issuer plc
      (the "Company") in connection with the above-referenced Registration
      Statement in respect of the proposed issue of Notes by the Company.

1.2   Unless otherwise defined, capitalised terms defined in the Issue
      Documents (as defined below) have the same meanings when used in this
      letter.

1.3   We have examined copies of the documents mentioned in the Schedule
      hereto and such other documents as we have considered necessary.

1.4   We have not made any investigation of, and do not express any opinion
      on, the law of any jurisdiction other than England and Wales.

1.5   The headings to paragraphs in this letter are for information purposes
      only and shall not otherwise form part of this letter.

2.    ASSUMPTIONS

2.1   In considering the documents referred to above and in rendering this
      opinion we have, without any further enquiry, assumed (save as expressly
      stated):

      (a)   the capacity, power and authority of each of the parties (other
            than the Company) to execute, deliver and perform the terms of the
            documents specified in Part I of Schedule (together, the "Issue
            Documents");


       Sidley Austin (UK) LLP is a limited liability partnership formed
          and registered under the laws of the State of Delaware. The
      offices listed above (other than London) are offices of associated
                          Sidley Austin partnerships.

      A list of partners' names and their professional qualifications is
        open for inspection at Woolgate Exchange 25 Basinghall Street,
      London, EC2V 5HA. All partners are either solicitors or registered
                               foreign lawyers.

                        Regulated by the Law Society.





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      (b)   the due execution and delivery of the Issue Documents;

      (c)   the conformity to original documents of any copy documents
            examined by us and that the copy of the Memorandum and Articles of
            Association of the Company examined by us is complete and up to
            date and would, if issued today, comply, as respects the Articles
            of Association, with Section 380 of the Companies Act 1985;

      (d)   that the Notes will be duly executed, issued and authenticated in
            accordance with the provisions of the Amended and Restated Issuer
            Trust Deed, the Issuer Paying Agent and Agent Bank Agreement and
            the Ninth Supplemental Trust Deed (each as defined in the
            Schedule);

      (e)   that no law of any jurisdiction outside England and Wales would
            render execution, delivery or issue illegal or ineffective and
            that, insofar as any obligation under any of the Issue Documents
            or the Notes is performed in, or is otherwise subject to, any
            jurisdiction other than England and Wales, its performance will
            not be illegal or ineffective by virtue of the law of that
            jurisdiction;

      (f)   that the information disclosed by our searches made today of
            the records at the office of the Registrar of Companies in
            London and at the Central Registry of Winding up petitions in
            relation to the Company was then complete, up to date and
            accurate and has not since then been materially altered or
            added to, and no notice of intention to appoint an
            administrator or an application for an administration order in
            respect of the Company has been presented or filed in any
            court in England and Wales;

      (g)   that the Company is not, and will not be on the date on which the
            Notes are issued, unable to pay its debts within the meaning of
            section 123 of the Insolvency Act 1986 (as amended) and will not
            become unable to do so in consequence of the transactions effected
            by the Issue Documents;

      (h)   that the draft Minutes referred to in Part II of the Schedule will
            represent a true record of the proceedings described therein of
            duly convened, constituted and quorate meetings of the Boards of
            Directors of the Company acting in the interests and for a proper
            purpose of the Company and that the relevant meetings will be duly
            held and that the authorisations to be given thereat will not
            subsequently been revoked or amended;

      (i)   that any factual matters referred to in each Issue Document will
            be true and accurate (including, without limitation, the accuracy
            of the representations and warranties therein);


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      (j)   that the relevant Issue Documents will in all material respects
            relevant hereto be executed and delivered substantially in the
            form of the relevant exhibit to the Registration Statement;

      (k)   that none of the parties to the Issue Documents has taken or will
            take any action in relation to the Notes (i) which would be a
            contravention of Section 19 of the Financial Services and Markets
            Act 2000 (the "FSMA") or (ii) in consequence of anything said or
            done by a person in the course of carrying on investment business
            (within the meaning of the FSMA) in contravention of that Section;

      (l)   that (i) none of the Issue Documents will be entered into and
            none of the Notes will be issued in consequence of a
            communication in relation to which there has been or will be a
            contravention of Section 21 of the FSMA and (ii) no person has
            communicated or will communicate any inducement or invitation
            to engage in investment activity (within the meaning of the
            FSMA) in connection with the Issue Documents or the issue of
            the Notes in contravention of Section 21 of the FSMA; and

      (m)   that any party to any of the Issue Documents which is subject to
            the supervision of any regulatory authority in the United Kingdom
            has complied and will comply with the requirements of such
            regulatory authority in connection with the issue, offering or
            sale of the Notes.

We express no opinion as to matters of fact.

3.    OPINION

Based on the foregoing and subject to such legal and other considerations and
qualifications as are stated herein, we are of the opinion that the Notes will
constitute valid and legally binding obligations of the Company. As a result,
those obligations would be enforceable in proceedings before the English
courts.

4.    QUALIFICATIONS

The opinions given in paragraph 3 of this letter are subject to the following
qualifications:

      (a)   We do not express any opinion on European Community law as it
            affects any jurisdiction other than England and Wales.

      (b)   Any enforcement of the obligations of the Company in
            proceedings before the English courts would be by way of grant
            of a remedy in the event of a breach of those obligations. The
            nature and availability of the remedies provided by the
            English courts would depend on the circumstances. These
            remedies, including an order by the court requiring the
            payment of damages or the payment of a sum due, would be
            available subject to the principles of law,


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            equity and procedures of general application. Some remedies,
            including an order by the court requiring specific performance of
            an obligation or the issue


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            of an injunction, would be entirely within the discretion of the
            court. The possibility of obtaining any remedy would be lost if
            proceedings were not to be commenced within certain time limits.
            The English courts have power to stay proceedings and may decline
            jurisdiction, notably if concurrent proceedings are brought
            elsewhere. Accordingly, enforcement of the obligations of the
            Company under the Notes would not be certain in every
            circumstance.

      (c) The obligations of the Company under the Notes will be subject to
          any law from time to time in force relating to liquidation or
          administration or any other law or legal procedure affecting
          generally the enforcement of creditors' rights.

5.    GENERAL

We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement. We also consent to the reference to Sidley Austin (UK)
LLP under the caption "Legal matters" in the Prospectus. In giving such
consent, we do not admit that we are "experts", within the meaning of the term
used in the Securities Act 1933, as amended, or the rules and regulations of
the SEC issued thereunder, with respect to any part of the Registration
Statement including this opinion as an exhibit or otherwise.

Yours faithfully,

/s/ Sidley Austin (UK) LLP
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                                   SCHEDULE

                                    PART I

1.    The issuer trust deed dated 19 January 2005 between the Company and The
      Bank of New York, exhibited as Exhibit 4.6.1 to the Registration
      Statement (the "Issuer Trust Deed").

2.    A form of supplementary issuer trust deed between the Company and The
      Bank of New York, exhibited as Exhibit 4.6.2 to the Registration
      Statement (the "Supplemental Issuer Trust Deed").

3.    The issuer paying agent and agent bank agreement amended and restated on
      25 January 2006 between, inter alios, the Company and Citibank, N.A.,
      exhibited as Exhibit 4.7 to the Registration Statement (the "Amended and
      Restated Issuer Paying Agent and Agent Bank Agreement").


                                    PART II

A draft of the Minutes of a Meeting of the Board of Directors of the Company
to be held on or about the Closing Date.


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