EXHIBIT 5.1



              [LETTERHEAD OF TROUTMAN SANDERS LLP APPEARS HERE]
 

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 preliminary prospectus, filed with the Securities and Exchange 
Commission (the "Commission") on July 29, 1996 (File No. 333-09033) as amended
by Amendment No. 1 filed with the Commission on August 28, 1996, and by 
Amendment No. 2 filed with the Commission on September 24, 1996, (as so 
amended, 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 filed as exhibits
to the 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, 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 filed as 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 acting giving 
effect to foreign governmental 



 
Southern Investments UK plc
September 26, 1996
Page 2

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 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 
caption "Legal Matters" in the Registration Statement.

                                    Very truly yours,

                                    TROUTMAN SANDERS LLP