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Exhibit 2(b).2.2
 SUPPLEMENTARY PROSPECTUS DATED 6 MARCH 2006
 
 NATIONAL GRID GAS HOLDINGS plc
 (incorporated with limited liability in England and Wales on 27 November 1998 under registered number 3675375)
 NATIONAL GRID GAS plc
 (incorporated with limited liability in England and Wales on 1 April 1986 under registered number 2006000)
 Euro 10,000,000,000
Euro Medium Term Note Programme
 Supplement Prospectus NGGH NGG Issuer Issuers FSMA th NGG Supplement Programme




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Acquisition of KeySpan
 The following text is extracted from the announcement issued by National Grid plc on 27
February 2006:National Grid and KeySpan today announce that they have reached agreement under which National
Grid will acquire KeySpan for $42.00 (£24.00) per share in cash. The terms of the agreement
value the equity of KeySpan at approximately $7.3 billion (£4.2 billion) and the enterprise
value of KeySpan at approximately $11.8 billion (£6.7 billion) (including estimated net debt of
approximately $4.5 billion (£2.6 billion) as at 31 December 2005).KeySpan is a major US energy delivery company. It is the largest distributor of natural gas in
the North-eastern US and the fifth largest in the US, with approximately 2.6 million customers
in New York, Massachusetts and New Hampshire. In addition, it operates an electricity
transmission and distribution system serving approximately 1.1 million customers in New York,
under a contract with the Long Island Power Authority (LIPA). KeySpan also owns and operates
6.7 GW of generation capacity in New York. Its other assets include investments in natural gas
pipeline and storage assets.
 Acquisition benefits
 KeySpan is an excellent strategic and operational fit with National Grid and a natural
extension of National Grids business. Together with the recently agreed acquisition of the
Rhode Island gas distribution assets from Southern Union Company, the acquisition of KeySpan
will build upon National Grids successful track record in the US.
 
    
    KeySpans gas distribution and electricity distribution and transmission businesses
operate in states where National Grid already has a presence and where it has strong
regulatory relationships. The geographic fit between the two companies will facilitate the
implementation of efficiency initiatives across the enlarged Group.
    
    The Acquisition will allow National Grid to deploy its core skills of owning and
operating network infrastructure within an incentive-based regulatory environment across a
larger rate base.
 In addition, National Grid will have a stronger US growth platform across its distribution
business including building on KeySpans investments in gas pipelines and gas storage.National Grid believes the Acquisition will create significant value and deliver a return on
invested capital greater than National Grids cost of capital. It is expected to be earnings
and cash flow enhancing1 in the first full year following Completion.National Grid expects to:
 
    
    Deliver identified integration savings of $200 million per year, through the
rationalisation of overlapping functions and the sharing of best practices.
    
    Unlock additional organic growth by investing in KeySpans gas distribution business.
    
    Invest in other growth opportunities including gas pipelines and storage.
 Generation
 KeySpans well managed generation business includes plants on Long Island (4.2 GW) which
operate under agreements that purchase their full production capacity on a full cost pass
through basis. The remaining 2.5 GW of capacity is located within the constrained New York City
load pocket.
 
 1
    
    On a Business Performance basis. 2




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Management
 Following Completion, Michael E. Jesanis will continue as CEO of the enlarged National Grid USA
and Bob Catell, Chairman and CEO of KeySpan, will join the Board as Deputy Chairman of National
Grid and Chairman of National Grid USA.
 Financing
 National Grid intends to finance the Acquisition wholly from borrowings. National Grid expects
that its credit ratings post Completion will be downgraded by no more than one notch and it
remains committed to its ratings target of an A range for both of its rated UK operating
companies.
 Financial Results
 For the year ended 31 December 2004, KeySpan reported earnings before interest, tax,
depreciation and amortisation of $1.5 billion (£0.9 billion) on revenues of $6.7 billion (£3.8
billion), and had net assets of $3.9 billion (£2.2 billion)2. KeySpans gas and
electricity delivery businesses accounted for 66 per cent. of its operating income for the year
ending 31 December 2004, and 75 per cent. of its assets as at that date. The corresponding
figures for generation are 33 per cent. and 17 per cent. respectively.
 Completion
 The Acquisition is subject to a number of conditions, including approval by National Grids and
KeySpans shareholders as well as certain regulatory and other consents and approvals in the
US. The principal regulatory approvals required are from the Federal Energy Regulatory
Commission and the states of New York and New Hampshire. The Acquisition also requires
clearance under US anti-trust and foreign investment laws. National Grid is targeting
Completion to take place by early 2007.For ease of reference, in the above statement: (i) all currency conversions between pounds
sterling and US dollars have been made at a rate of $1.75: £1.00; and (ii) financial
information for KeySpan is presented in US GAAP.
 Amendment to the Terms and Conditions
 The Terms and Conditions of the Instruments have been amended pursuant to a Trust Deed
between the Issuers and the Trustee dated 6 March 2006 by the deletion of the previous
Conditions 4.3 (ii) and (iii) and the addition of the following paragraphs as new Conditions
4.3(ii) and (iii):
 (ii)
    
    Delay in publication of Index if sub-paragraph (i) of the definition of Index Figure
is applicable: If the Index Figure which is normally published in the seventh month and
which relates to the eighth month (the relevant month) before the month in which a
payment is due to be made is not published on or before the fourteenth business day before
the date on which such payment is due (the date for payment), the Index Figure
applicable to the month in which the date for payment falls shall be (1) such substitute
index figure (if any) as the Trustee considers (acting solely on the advice of the
Indexation Advisor) to have been published by the United Kingdom Debt Management Office or
the Bank of England, as the case may be, for the purposes of indexation of payments on the
Reference Gilt or, failing such publication, on any one or more issues of index-linked
Treasury Stock selected by an Indexation Adviser (and approved by the Trustee (acting
solely on the advice of the Indexation Advisor)) or (2) if no such determination is made
by such Indexation Adviser within seven days, the Index Figure last published (or, if
later, the substitute index figure last determined pursuant to Condition 4.3(i)) before
the date for payment.(iii)
    
    Delay in publication of Index if sub-paragraph (ii) and/or (iii) of the definition
of Index Figure is applicable: If the Index Figure relating to any month (the calculation
month) which is required to be taken into account for the purposes of the determination
of the Index Figure for any date is not published on or before the fourteenth business day
before the date on which such payment is due (the date for payment), the Index Figure
applicable for the relevant calculation month shall be (1)
 
 2
    
    US GAAP. 3




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such substitute index figure (if any) as the Trustee considers (acting solely on the
advice of the Indexation Advisor) to have been published by the United Kingdom Debt
Management Office or the Bank of England, as the case may be, for the purposes of
indexation of payments on the Reference Gilt or, failing such publication, on any one or
more issues of index-linked Treasury Stock selected by an Indexation Adviser (and
approved by the Trustee (acting solely on the advice of the Indexation Advisor)) or (2)
if no such determination is made by such Indexation Adviser within seven days, the Index
Figure last published (or, if later, the substitute index figure last determined pursuant
to Condition 4.3(i)) before the date for payment.
 4