August 7, 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  communication  is being  distributed  to all KeySpan  Corporation
employees.


KEYSPAN


August 2006



                 Important Information Regarding your Proxy Vote
            for your KeySpan Common Stock in the KeySpan 401(k) Plan



Dear 401(k) Plan Participant:

If you were a  participant  in the KeySpan  401(k) Plan and had an investment in
the KeySpan  Common stock fund on July 3rd 2006 proxy  materials  regarding  the
Annual Meeting of Shareholders of KeySpan Corporation were recently  distributed
to you. The Proxy  statement  provides you with  information  about the proposed
merger  providing for the  acquisition of KeySpan by National Grid plc and other
matters to be considered at the Annual Meeting. This letter is being sent to you
to explain  the voting  procedures  for  KeySpan  shares held within your 401(k)
Plan.

Vanguard  Fiduciary Trust Company  ("Vanguard"),  pursuant to the KeySpan 401(k)
Plan Trust Agreement  effective  March 12, 2000 between KeySpan  Corporation and
Vanguard  ("Trust  Agreement"),  was  appointed  as Trustee to vote all  KeySpan
shares  held in the 401(k) Plan for which  timely  voting  instructions  are not
received. Generally, unvoted shares of KeySpan stock held in the 401(k) Plan are
voted by Vanguard in the same  proportion  as those shares which have been voted
by other 401(k) shareholders.  This voting procedure applies to all proposals in
the  current  proxy  with the  exception  of  Proposal  1 related  to the merger
providing for the acquisition of KeySpan by National Grid plc.

Per the terms of the Trust  Agreement,  in the event of a merger or acquisition,
Vanguard is required to vote at its  discretion  all KeySpan  shares held in the
401(k) Plan for which timely  voting  instructions  have not been  received.  As
indicated  on your proxy card you will need to vote your  401(k)  Plan shares by
August 14, 2006 in order for your vote to be  considered  timely.  In voting any
shares for which it does not receive timely instructions,  Vanguard will vote in
its discretion and is required under the Employee Retirement Income Security Act
of  1974  to  vote  the  shares  in the  economic  best  interests  of the  Plan
participants with respect to their 401(k) Plan account.

If you do not vote your  shares in the  401(k)  Plan by August 14 you still have
the  ability to vote any shares you hold  outside  the 401(k)  Plan prior to the
closing of the polls at the Annual Meeting of Shareholders on August 17.

Please take this  opportunity  to vote today if you have not already  voted your
proxy.  To expedite  your vote you can vote by  telephone or Internet 24 hours a
day 7 days a week.


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To vote  using the  telephone,  call  1-800-652-VOTE  (8683).  To vote using the
Internet  go  to:  www.computershare.com/expressvote.   If  you  are  voting  by
telephone  or by the  Internet  have your proxy card  available to refer to your
control number and follow the simple voting instructions.

If you have any questions or need  assistance  voting your shares,  including if
you have misplaced your proxy card, please call the Company's proxy solicitation
agent D.F. King & Co., Inc. toll free at 1-800-628-8536.


Sincerely,


The KeySpan Investment Review Committee


    /s/Gerald Luterman,                               /s/Richard A. Rapp, Jr.
    Executive Vice President                          Vice President
    & Chief Financial Officer                         Energy Transactions


    /s/Michael Taunton                                /s/Justin Orlando,
    Senior Vice President, Treasurer                  Vice President
    & Chief Risk Officer                              Human Resources



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 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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