EXHIBIT 5.1

               [LETTERHEAD OF TROUTMAN SANDERS LLP APPEARS HERE]


                               November 18, 1996

Southern Investments UK plc
800 Park Avenue, Aztec West
Almondsbury
Bristol BS12 4SE, England

RE:  Registration Statement on Form S-1

Gentlemen:

     We have acted as counsel to Southern Investments UK plc (the "Company") in
connection with the preparation of a Registration Statement on Form S-1,
including a final prospectus, filed with the Securities and Exchange Commission
(the "Commission") on the date hereof (the "Registration Statement"), for the
registration under the Securities Act of 1933, as amended (the "Act"), of Senior
Notes (the "Senior Notes") to be issued by the Company pursuant to an indenture
between the Company and the trustee named therein (the "Indenture"), and
pursuant to the supplemental indenture between the Company and the trustee named
therein (the "First Supplemental Indenture"), in each case in the respective
forms incorporated by reference as exhibits to the Registration Statement.

     In its capacity, we have examined originals, or copies certified or
otherwise identified to our satisfaction, of such documents as we have deemed
necessary as a basis for the opinion hereinafter expressed.  In our
examinations, we have assumed the genuineness of all signatures, the legal
capacity of natural persons, the authenticity of all documents presented to us
as originals and the conformity with the originals of all documents submitted to
us as copies.

     Based upon such examination and the assumptions set forth herein, subject
to the limitations set forth herein and having considered such questions of law
as we have deemed necessary as a basis for the opinion expressed below, we are
of the opinion that, upon compliance with the pertinent provisions of the Act
and the Trust Indenture Act of 1939, as amended, upon the adoption of
appropriate resolutions of the Board of Directors of the Company or a duly
authorized committee thereof, when the Indenture and the Senior Notes have been
duly executed by the parties thereto substantially in the form incorporated by
reference as an exhibit to the Registration Statement and the Senior Notes have
been duly authenticated by the Trustee in the manner contemplated in the
Indenture and duly delivered to and paid for by the Underwriters (as defined in
the attached opinion of Shearman & Sterling) in accordance with the terms of the
Underwriting Agreement (as defined in the attached opinion of Shearman &
Sterling), the Senior Notes will constitute valid and legally binding
obligations of the Company, enforceable against the Company in accordance with
their terms, except as enforcement thereof may be limited by applicable
bankruptcy, insolvency (including, without limitation, all laws relating to
fraudulent transfers), reorganization, moratorium or similar laws affecting
enforcement of creditors' rights generally and except as enforcement thereof is
subject to possible judicial action giving effect to foreign governmental
actions or foreign laws affecting creditors' rights and to general principles of
equity, including, without limitation, concepts of materiality, reasonableness,
good faith and fair dealing (regardless of whether enforcement is considered in
a proceeding in equity or at law).

 
Southern Investments UK plc
November 18, 1996
Page 2

     In rendering the opinion expressed above, we have assumed the due existence
of each party to each document referred to therein, that the execution and
delivery of each such document will be effected in accordance with all laws,
regulations, procedures and contractual restrictions applicable to the party
taking such action and that such action will not violate any such law,
regulation, contractual restriction or procedure.

     We are attorneys admitted to practice in the State of Georgia, and we do
not express any opinion herein concerning any law other than the law of the
State of Georgia, the State of New York and the federal law of the United
States.  To the extent that our opinion expressed herein relates to the law of
the State of New York, we have relied exclusively on the opinion of Shearman &
Sterling attached hereto as Exhibit A.

     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the statements with respect to our firm under the
captions "Legal Opinions," and "Legal Matters" in the Registration Statement.

                              Very truly yours,

                              /s/ Troutman Sanders LLP
                              -----------------------------
                              TROUTMAN SANDERS LLP

 
                        [SHEARMAN & STERLING LETTERHEAD]



                              November 18, 1996

Troutman Sanders LLP
NationsBank Plaza
600 Peachtree Street, N.E.
Suite 5200
Atlanta, GA  30308-2216



                   $168,000,000 6.375% Senior Notes due 2001
                   $332,000,000 6.800% Senior Notes due 2006
                            Southern Investments UK plc
                            ---------------------------


Ladies and Gentlemen:

          We have acted as counsel to Lehman Brothers Inc., Merrill Lynch,
Pierce, Fenner & Smith Incorporated and J.P. Morgan Securities Inc.
(collectively, the "Underwriters")  in connection with the purchase by the
Underwriters pursuant to the Underwriting Agreement (the "Underwriting
Agreement") entered into between the Underwriters and Southern Investments UK
plc, a public limited company incorporated under the laws of England and Wales
(the "Company"), of the Company's 6.375% Senior Notes due 2001 and the Company's
6.800% Senior Notes due 2006 (the "Senior Notes") to be issued under an
Indenture (as amended by a First Supplemental Indenture, the "Indenture") to be
entered into between the Company and Bankers Trust Company, as trustee (the
"Trustee").  In this connection, the Company has prepared a Registration
Statement on Form S-1 (Registration No. 333-09033), which was filed with the
Securities and Exchange Commission on July 29, 1996 (as amended, the "First
Registration Statement") and a Registration Statement on Form S-1, which is
being filed with the Securities and Exchange Commission, relating to the
registration under the Securities Act of 1933, as amended (the "Securities
Act"), of the Senior Notes.  The form of the Indenture is filed as an exhibit to
the First Registration Statement.

          In this capacity, we have examined originals, or copies certified or
otherwise identified to our satisfaction, of such documents as we have deemed
necessary as a basis for the opinion hereinafter expressed.  In our
examinations, we have assumed the genuineness of all signatures, the legal
capacity of natural persons, the authenticity of all documents presented to us
as originals and the conformity with the originals of all documents submitted to
us as copies.

 
          Based upon such examination and the assumptions set forth herein,
subject to the limitations set forth herein and having considered such questions
of law as we have deemed necessary as a basis for the opinion expressed below,
we are of the opinion that, when the Indenture and the Senior Notes have been
duly executed by the parties thereto substantially in the form filed as an
exhibit to the First Registration Statement and the Senior Notes have been duly
authenticated by the Trustee in the manner contemplated in the Indenture and
duly delivered to and paid for by the Underwriters in accordance with the terms
of the Underwriting Agreement, the Senior Notes will constitute valid and
legally binding obligations of the Company, enforceable against the Company in
accordance with their terms, except as enforcement thereof may be limited by
applicable bankruptcy, insolvency (including, without limitation, all laws
relating to fraudulent transfers), reorganization, moratorium or similar laws
affecting enforcement of creditors' rights generally and except as enforcement
thereof is subject to possible judicial action giving effect to foreign
governmental actions or foreign laws affecting creditors' rights and to general
principles of equity, including, without limitation, concepts of materiality,
reasonableness, good faith and fair dealing (regardless of whether enforcement
is considered in a proceeding in equity or at law).

          In rendering the opinion expressed above, we have assumed the due
existence of each party to each document referred to therein, that the execution
and delivery of each such document will be effected in accordance with all laws,
regulations, procedures and contractual restrictions applicable to the party
taking such action and that such action will not violate any such law,
regulation, contractual restriction or procedure.

          We are attorneys admitted to practice in the State of New York and we
do not express any opinion herein concerning any law other than the law of the
State of New York and the federal law of the United States.

          This opinion is being rendered solely for your benefit in connection
with your rendering an opinion to the Company in response to Exhibit 5 to form
S-1 under the Securities Act in connection with the registration of the Senior
Notes under the Securities Act and we hereby consent to your attaching this
opinion as an exhibit to such opinion.  This opinion may not be relied upon for
any other purpose or furnished, used, circulated, quoted or otherwise referred
to for any other purpose without our prior written consent.

                                Very truly yours,

                                /s/ Shearman & Sterling
                                -----------------------------
                                SHEARMAN & STERLING