August 2, 2006

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                            SCHEDULE 14A INFORMATION

                  Proxy Statement Pursuant to Section 14(a) of
            the Securities and Exchange Act of 1934 (Amendment No. )

Filed by the Registrant  [X]
Filed by a Party other than the Registrant  [ ]

Check the appropriate box:
[ ]     Preliminary Proxy Statement
[ ]     Confidential, For Use of the Commission Only (as permitted by
        Rule 14a-6(e)(2))
[ ]     Definitive Proxy Statement
[X]     Definitive Additional Materials
[ ]     Soliciting Material Pursuant to Section 240.14a-12

                              KeySpan Corporation
                              -------------------
                (Name of Registrant as Specified in Its Charter)

                                     (N/A)
                                     -----
    (Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (Check the appropriate box):
[X]     No fee required.
[ ]     Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

(1)  Title of each class of securities to which transaction applies:
     N/A______________________________________________________________
(2)  Aggregate number of securities to which transaction applies:
     N/A______________________________________________________________
(3)  Per unit price or other underlying value of transaction  computed  pursuant
     to Exchange  Act Rule 0-11 (set forth the amount on which the filing fee is
     calculated and state how it was determined):
     N/A______________________________________________________________
(4)  Proposed maximum aggregate value of transaction:
     N/A______________________________________________________________
(5)  Total fee paid:
     N/A______________________________________________________________




[ ]       Fee paid previously with preliminary materials.

[ ]       Check box if any part of the fee is offset as provided by Exchange Act
          Rule  0-11(a)(2)  and identify the filing for which the offsetting fee
          was  paid  previously.   Identify  the  previous  filing  registration
          statement number, or the Form or Schedule and date of its filing.

(1)  Amount Previously Paid:
     N/A______________________________________________________________
(2)  Form, Schedule or Registration Statement No.:
     N/A______________________________________________________________
(3)  Filing Party:
     N/A______________________________________________________________
(4)  Date Filed:
     N/A______________________________________________________________












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The  following  letter  is being  mailed  to  unvoted  stockholders  of  KeySpan
Corporation who own 100 or more shares.

KeySpan                                                    One MetroTech Center
                                                  Brooklyn, New York 11201-3850

                               IMPORTANT REMINDER
                          PLEASE VOTE YOUR PROXY TODAY

                                                                 August 2, 2006

Dear KeySpan Stockholder:

     We recently  distributed  proxy  materials  regarding the Annual Meeting of
Stockholders  of KeySpan  Corporation.  The meeting is  scheduled  to be held on
August 17, 2006. If you have not yet voted,  please take one moment of your time
now to cast your vote for this important meeting.

     Your vote is  important  no matter  how many  shares  you hold.  Please act
promptly to vote your shares. Telephone and internet voting is available to most
stockholders.  See  instructions  regarding  voting on the reverse  side of this
letter.

     For the reasons more fully described in the Proxy Statement, dated July 11,
2006, your Board of Directors unanimously recommends that you vote:

1.   "FOR"  the  adoption  of the  Agreement  and  Plan of  Merger,  dated as of
     February 25, 2006,  among  National Grid plc,  National Grid US8 Inc.,  and
     KeySpan  pursuant  to  which,  upon the  merger  becoming  effective,  each
     outstanding  share of common stock of KeySpan  will be  converted  into the
     right to receive $42.00 in cash, without interest;

2.   "FOR" the election of ten directors;

3.   "FOR" the ratification of Deloitte & Touche LLP, as independent  registered
     public accountants for the year ending December 31, 2006; and

4.   "AGAINST" the stockholder proposal to adopt simple majority vote.

     The Board of Directors has  unanimously  determined that the merger is fair
to and in the best  interests of our  stockholders  and has approved the merger.
The adoption of the merger  agreement  requires the approval of the holders of a
majority of the combined voting power of the outstanding  shares of common stock
entitled  to  vote  thereon.  Accordingly,  the  vote  of  all  stockholders  is
important.  If a KeySpan  stockholder  does not vote,  it has the same effect as
voting against the merger. Please act today to vote your proxy!

     If you have any  questions or need  assistance  voting your shares,  please
call  our  proxy  solicitation  agent,  D. F.  King & Co.,  Inc.,  toll-free  at
1-800-628-8536.

     Thank you for your cooperation.

                                                  Sincerely,


                                                  /s/Robert B. Catell
                                                  -------------------
                                                  ROBERT B. CATELL
                                                  CHAIRMAN AND CHIEF EXECUTIVE
                                                  OFFICER


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                               3 EASY WAYS TO VOTE

     Help your  company  avoid the  expense  of further  solicitation  by voting
today. You may use one of the following simple methods to vote your shares:

1.   Vote by  Telephone.  Call the  toll-free  number listed for this purpose on
     your proxy or voting  instruction  form. Have your control number listed on
     the form ready and follow the simple instructions.

2.   Vote by  Internet.  Go to the  website  listed  on  your  proxy  or  voting
     instruction  form.  Have your control  number  listed on the form ready and
     follow the simple instructions.

3.   Vote by Mail. Mark, sign, date and return your proxy or voting  instruction
     form in the postage-paid return envelope provided.


                            STREET NAME STOCKHOLDERS
                            ------------------------

     Please refer to your proxy or voting  instruction  form for instructions on
how to vote.  Your broker or bank cannot vote your shares on the merger proposal
unless it receives your specific instructions.

                                PLEASE ACT TODAY
                                ----------------

- --------------------------------------------------------------------------------
                                  YOUR VOTE IS
                                    IMPORTANT

Please help your company save additional  solicitation costs by signing,  dating
and mailing your proxy or voting  instruction form today. If you submit a signed
proxy card without giving  specific voting  instructions  with respect to any or
all  proposals,  you give the named proxies the authority to vote, in accordance
with the Board's recommendations,  on each such proposal and in their discretion
on any other matter that may arise at the meeting. However, a failure to vote is
equivalent to a vote against the merger agreement. Please refer to your proxy or
voting instruction form for instructions on how to vote. Please return your vote
immediately.  If you have any questions or need  assistance  voting your shares,
please call our proxy solicitation  agent, D. F. King & Co., Inc.,  toll-free at
1-800-628-8536.
- --------------------------------------------------------------------------------

In connection with the proposed merger, the Company has filed a definitive proxy
statement with the Securities and Exchange Commission.  BEFORE MAKING ANY VOTING
OR  INVESTMENT  DECISION,  THE  COMPANY  STOCKHOLDERS  ARE  URGED  TO  READ  THE
DEFINITIVE PROXY STATEMENT BECAUSE IT CONTAINS  IMPORTANT  INFORMATION ABOUT THE
PROPOSED MERGER. The definitive proxy statement is also available free of charge
at  the  Securities  and  Exchange   Commission's  website,   www.sec.gov,   and


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stockholders  of the  Company are also able to obtain  additional  copies of the
definitive proxy statement free of charge by directing their requests to KeySpan
Corporation One MetroTech Center, Brooklyn, New York 11201-3850.

The  Company  and its  directors  and  executive  officers  may be  deemed to be
participants in the  solicitation of proxies from its stockholders in connection
with the proposed merger.  Information concerning the interests of the Company's
participants in the  solicitation is set forth in the Company's proxy statements
and Annual  Reports  on Form 10-K,  previously  filed  with the  Securities  and
Exchange  Commission,  and in the  definitive  proxy  statement  relating to the
merger.








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Additional Information and Where to Find It
- -------------------------------------------

In connection with the proposed merger, the Company has filed a definitive proxy
statement with the Securities and Exchange Commission.  BEFORE MAKING ANY VOTING
OR  INVESTMENT  DECISION,  THE  COMPANY  STOCKHOLDERS  ARE  URGED  TO  READ  THE
DEFINITIVE PROXY STATEMENT BECAUSE IT CONTAINS  IMPORTANT  INFORMATION ABOUT THE
PROPOSED MERGER. The definitive proxy statement is also available free of charge
at  the  Securities  and  Exchange   Commission's  website,   www.sec.gov,   and
stockholders  of the  Company are also able to obtain  additional  copies of the
definitive proxy statement free of charge by directing their requests to KeySpan
Corporation One MetroTech Center, Brooklyn, New York 1120-3850.

The  Company  and its  directors  and  executive  officers  may be  deemed to be
participants in the  solicitation of proxies from its stockholders in connection
with the proposed merger.  Information concerning the interests of the Company's
participants in the  solicitation is set forth in the Company's proxy statements
and Annual  Reports  on Form 10-K,  previously  filed  with the  Securities  and
Exchange  Commission,  and in the  definitive  proxy  statement  relating to the
merger.






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