Exhibit 5.1




                  SIDLEY AUSTIN            |BEIJING   GENEVA      SAN FRANCISCO
                  WOOLGATE EXCHANGE        |BRUSSELS  HONG KONG   SHANGHAI
SIDLEY AUSTIN     25 BASINGHALL STREET     |CHICAGO   LONDON      SINGAPORE
- ----------------| LONDON EC2V 5HA          |DALLAS    LOS ANGELES TOKYO
SIDLEY          | DX NUMBER 580 LONDON CITY|FRANKFURT NEW YORK    WASHINGTON, DC
                  +44 (0) 20 7360 3600     |
                  +44 (0) 20 7626 7937 FAX |



Granite Master Issuer plc
Fifth Floor
100 Wood Street
London
EC2V 7EX




                                                               April 20, 2006




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");

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



  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.

    The offices listed above (other than London) are offices of associated
           Sidley Austin Partnerships. Regulated by the Law Society.



SIDLEY AUSTIN
- -------------|
SIDLEY       |


Page 2


      (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 Sixth 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);

      (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;




                                      2


SIDLEY AUSTIN
- -------------|
SIDLEY       |


Page 3


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



                                      3


SIDLEY AUSTIN
- -------------|
SIDLEY       |


Page 4


            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 under the caption "Legal matters" in the Offering Circular. 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





                                      4


SIDLEY AUSTIN
- -------------|
SIDLEY       |


Page 5


                                   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.



                                       5