EXHIBIT 5.1



                              Troutman Sanders LLP
                              600 Peachtree Street
                             Atlanta, Georgia 30303
                                  404-885-3000



                                  June 25, 1997



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

         Re:      Southern Investments UK plc Exchange Offer

Gentlemen:

         We have acted as special U.S. counsel to Southern Investments UK plc
(the "Company") and Southern Investments UK Capital Trust I (the "Trust") in
connection with the preparation of a Registration Statement on Form S-4 (File
Nos. 333-26939 and 333-26939-01), as amended (the "Registration Statement"),
which has been filed with the Securities and Exchange Commission under the
Securities Act of 1933, as amended (the "Act"), relating to the proposed offer
to exchange up to $82,000,000 aggregate liquidation amount of the Trust's 8.23%
Exchange Subordinated Capital Income Securities (the "Exchange Capital
Securities") for a like liquidation amount of its outstanding 8.23% Subordinated
Income Capital Securities (the "Original Capital Securities"), of which
$82,000,000 aggregate liquidation amount are issued and outstanding. The
Exchange Capital Securities will be guaranteed (the "Exchange Guarantee") by the
Company pursuant to a guarantee agreement (the "Guarantee Agreement") between
the Company and Bankers Trust Company, as trustee (the "Guarantee Trustee"),
with respect to the payment of distributions and payments upon liquidation,
redemption and otherwise to the extent set forth in the Prospectus (the
"Prospectus") filed as part of the Registration Statement.

         In connection with the offer to exchange the Exchange Capital
Securities for the Original Capital Securities, the Company will also offer to
exchange $84,537,000 aggregate principal amount of its 8.23% Exchange
Subordinated Debentures due February 1, 2027 (the "Exchange Subordinated
Debentures") for a like aggregate principal amount of its 8.23% Subordinated
Debentures due February 1, 2027 (the "Original Subordinated Debentures"), which
were purchased by the Trust with the proceeds of the Original Capital
Securities. Like the Exchange Capital Securities, the Exchange Subordinated
Debentures and the Exchange Guarantee will be registered under the Act.

Southern Investments UK plc
June 25, 1997
Page 2


         The Original Capital Securities were, and the Exchange Capital
Securities are being, issued pursuant to the Amended and Restated Declaration of
Trust dated as of January 29, 1997 among the Company, as sponsor, Bankers Trust
Company, as institutional trustee, Bankers Trust (Delaware), as Delaware
trustee, and the regular trustees named therein. The Original Capital Securities
were, and the Exchange Capital Securities will be, guaranteed by the Company on
a subordinated basis with respect to distributions and payments upon
liquidation, redemption and otherwise pursuant to the Guarantee Agreement. The
Original Subordinated Debentures were, and the Exchange Subordinated Debentures
will be, issued pursuant to an Indenture dated as of January 29, 1997 (the
"Indenture") among the Company, Bankers Trust Company, as trustee, and Bankers
Trust Luxembourg S.A., as paying agent and transfer agent.

         We have reviewed copies of the Registration Statement and the
Prospectus and such other documents as we have deemed necessary or appropriate
as a basis for the opinion set forth below.

         Based on the foregoing, we are of the opinion that:

                  (i) assuming (a) due authorization, execution and delivery of
         the Indenture, (b) establishment of the terms of the Exchange
         Subordinated Debentures in conformity with the Indenture and (c) due
         execution, delivery, authentication and issuance of the Exchange
         Subordinated Debentures in accordance with the Indenture and exchange
         for a like principal amount of validly tendered Original Subordinated
         Debentures, the Exchange Subordinated Debentures will constitute valid
         and binding obligations of the Company entitled to the benefits of the
         Indenture and enforceable against the Company in accordance with their
         terms, except as enforcement thereof may be limited by bankruptcy,
         insolvency (including, without limitation, all laws relating to
         fraudulent transfer), reorganization, moratorium or similar laws
         affecting creditors' rights generally and except as enforcement thereof
         is subject to general principles of equity (regardless of whether
         enforcement is considered in a proceeding in equity or at law); and

                  (ii) assuming due authorization, execution and delivery of the
         Guarantee Agreement by the Company and the Guarantee Trustee, the
         Exchange Guarantee will constitute a valid and binding obligation of
         the Company enforceable against the Company in accordance with its
         terms, except as enforcement thereof may be limited by bankruptcy,
         insolvency (including, without limitation, all laws relating to
         fraudulent transfer), reorganization, moratorium or similar laws
         affecting creditors' rights generally and except as enforcement thereof
         is subject to general principles of equity (regardless of whether
         enforcement is considered in a proceeding in equity or at law).

Southern Investments UK plc
June 25, 1997
Page 3

         In rendering the foregoing opinion, with respect to matters of New York
law, we have relied on the opinion of Shearman & Sterling attached hereto as
Annex I.

         We consent to the filing of this opinion as an exhibit to the
Registration Statement. We also consent to the reference to Troutman Sanders LLP
under the caption "Validity of Exchange Capital Securities" in the Registration
Statement. In giving the foregoing consent, we do not hereby admit that we come
within the category of persons whose consent is required under Section 7 of the
Securities Act of 1933, as amended, or the rules and regulations of the
Commission thereunder.

                                                     Very truly yours,

                                                     /s/Troutman Sanders LLP

                                                     TROUTMAN SANDERS LLP



                                                                         ANNEX I

                               Shearman & Sterling
                              599 Lexington Avenue
                         New York, New York 10022-6069


 June 25, 1997


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


                           Southern Investments UK plc
                     Southern Investments UK Capital Trust I



Ladies and Gentlemen:

                  We have acted as special New York counsel to Southern
Investments UK Capital Trust I, a statutory business trust organized under the
Business Trust Act (the "Delaware Act") of the State of Delaware (Chapter 38,
Title 12, of the Delaware Code, 12 Del. C. Section 3801 et seq.)(the "Trust")
and Southern Investments UK plc, a public limited company incorporated under the
laws of England and Wales (the "Company" and, together with the Trust, the
"Offerors"), in connection with the filing by the Offerors of a registration
statement on Form S-4 (Registration No. 333-26939) (the "Registration
Statement") under the Securities Act of 1933, as amended (the "Securities Act").
Pursuant to the Registration Statement, the Offerors are offering to exchange
(i) 8.23% Exchange Subordinated Capital Income Securities (the "Exchange Capital
Securities") for a like liquidation amount of the Trust's 8.23% Subordinated
Capital Income Securities (the "Original Capital Securities"), (ii) 8.23%
Exchange Subordinated Debentures (the "Exchange Subordinated Debentures") for a
like aggregate principal amount of the Company's 8.23% Subordinated Debentures
(the "Original Subordinated Debentures") and (iii) a guarantee agreement dated
as of January 29, 1997 (the "Guarantee Agreement") between the Company and
Bankers Trust Company, as trustee (the "Guarantee Trustee") referring to an
original guarantee (the "Original Guarantee") and an exchange guarantee (the
"Exchange Guarantee).

                  The Original Capital Securities were, and the Exchange Capital
Securities are being, issued pursuant to the Amended and Restated Declaration of
Trust dated as of





                                        2

January 29, 1997 among the Company, as sponsor, Bankers Trust Company, as
trustee, Bankers Trust (Delaware), as trustee and the regular trustees. The
Original Capital Securities were, and the Exchange Capital Securities will be,
guaranteed by the Company on a subordinated basis with respect to distributions
and payments upon liquidation, redemption and otherwise pursuant to the
Guarantee Agreement. The Original Subordinated Debentures were, and the Exchange
Subordinated Debentures will be, issued pursuant to an Indenture dated as of
January 29, 1997 (the "Indenture") among the Company, Bankers Trust Company, as
trustee (the "Indenture Trustee"), and Bankers Trust Luxembourg, as paying agent
and transfer agent.

                  In our capacity as special New York counsel to the Offerors,
we have examined originals, or copies identified to our satisfaction, of such
documents as we have deemed necessary as a basis for the opinions hereinafter
expressed. In our examinations, we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals and
the conformity with the originals of all documents submitted to us as copies.

                  Our opinions set forth below are limited to the laws of the
State of New York and the federal laws of the United States and we do not
express any opinion herein concerning any other law.

                  Based upon and subject to the foregoing, we are of the opinion
that:

                  (i) assuming (a) due authorization, execution and delivery of
         the Indenture by the Company and the Indenture Trustee, (b)
         establishment of the terms of the Exchange Subordinated Debentures in
         conformity with the Indenture and (c) due execution, delivery,
         authentication and issuance of the Exchange Subordinated Debentures in
         accordance with the Indenture and exchange for a like principal amount
         of validly tendered Original Subordinated Debentures, the Exchange
         Subordinated Debentures will constitute valid and binding obligations
         of the Company entitled to the benefits of the Indenture and
         enforceable against the Company in accordance with their terms, except
         as enforcement thereof may be limited by bankruptcy, insolvency
         (including, without limitation, all laws relating to fraudulent
         transfer), reorganization, moratorium or similar laws affecting
         creditors' rights generally and except as enforcement thereof is
         subject to general principles of equity (regardless of whether
         enforcement is considered in a proceeding in equity or at law); and

                  (ii) assuming due authorization, execution and delivery of the
         Guarantee Agreement by the Company and the Guarantee Trustee, the
         Exchange Guarantee will constitute a valid and binding obligation of
         the Company enforceable against the Company in accordance with its
         terms, except as enforcement thereof may be limited by bankruptcy,
         insolvency (including, without limitation, all laws relating to
         fraudulent transfer), reorganization, moratorium or similar laws
         affecting creditors' rights generally and except as enforcement thereof
         is subject to general principles of





                                        3

         equity (regardless of whether enforcement is considered in a proceeding
         in equity or at law).

                  In rendering the opinion expressed above, we have assumed the
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.

                  This opinion is furnished solely for your benefit in
connection with your rendering an opinion to the Company in response to Exhibit
5 to the Registration Statement and we hereby consent to your attaching this
opinion as an annex to such opinion. This opinion may not be relied upon for any
other purpose, or quoted to or relied upon by any other person, firm or entity
for any purpose, without our prior written consent.


                                                    Very truly yours,

                                                  /s/Shearman & Sterling