Exhibit EX-99.1

National Grid plc
Announces Sale of Seneca Upshur drilling business for $152.5 million

On Friday 23 September, 2011, National Grid entered into a purchase agreement with PDC Mountaineer, LLC for the sale of Seneca-Upshur Petroleum, LLC (“Seneca”) for a sale price of $152.5 million in cash together with an adjustment for working capital.

Tom King, National Grid’s Executive Director and President, US commented:? “Seneca was part of the KeySpan business that National Grid acquired in August 2007. The sale is part of our ongoing programme to focus the business on our core regulated gas and electricity transmission and distribution operations and related activities.”?

Seneca is a gas and oil exploration and production company operating primarily in West Virginia and Pennsylvania?. In 2010/11 Seneca contributed a loss of £4.5m to National Grid’s earnings before interest and tax* of £3.6bn.?

Barclays Capital acted as financial advisor for National Grid in this transaction.


John Dawson	+44 (0) 20 7004 3170	+44 (0) 7810831944(m)
George Laskaris	+1 718 403 2526	+1 917 375 0989 (m)
Andy Mead	+44 (0) 20 7004 3166	+44 (0) 77 5289 0787 (m)
Michael Smart	+44 (0) 20 7004 3214	+44 (0) 77 6729 8988 (m)
Iwan Hughes	+44 (0) 20 7004 3169	+44 (0) 79 0040 5898 (m)


Chris Mostyn		+44 (0) 20 7004 3149		+44 (0) 77 74827710 (m)

This announcement contains certain statements that are neither reported financial results nor other historical information. These statements are forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These statements include information with respect to National Grid’s financial condition, its results of operations and businesses, strategy, plans and objectives. Words such as ‘anticipates’, ‘expects’, ‘intends’, ‘plans’, ‘believes’, ‘seeks’, ‘estimates’, ‘targets’, ‘may’, ‘will’, ‘continue’, ‘project’ and similar expressions, as well as statements in the future tense, identify forward-looking statements. These forward-looking statements are not guarantees of National Grid’s future performance and are subject to assumptions, risks and uncertainties that could cause actual future results to differ materially from those expressed in or implied by such forward-looking statements. Many of these assumptions, risks and uncertainties relate to factors that are beyond National Grid’s ability to control or estimate precisely, such as such as changes in laws or regulations and decisions by governmental bodies or regulators; breaches of, or changes in, environmental, climate change and health and safety laws or regulations; network failure or interruption, the inability to carry out critical non-network operations and damage to infrastructure; performance against regulatory targets and standards, including delivery of costs and efficiency savings; customers and counterparties failing to perform their obligations to National Grid; and unseasonable weather affecting energy demands. Other factors that could cause actual results to differ materially from those described in this announcement include fluctuations in exchange rates, interest rates, commodity price indices and settlement of hedging arrangements; restrictions in National Grid’s borrowing and debt arrangements; changes to credit ratings of National Grid and its subsidiaries; adverse changes and volatility in the global credit markets; National Grid’s ability to access capital markets and other sources of credit in a timely manner and other sources of credit on acceptable terms; deflation or inflation; the seasonality of National Grid’s businesses; the future funding requirements of National Grid’s pension schemes and other post-retirement benefit schemes, and the regulatory treatment of pension costs; the loss of key personnel or the inability to attract, train or retain qualified personnel; new or revised accounting standards, rules and interpretations, including changes of law and accounting standards that may affect National Grid’s effective rate of tax; incorrect assumptions or conclusions underpinning business development activity, and any unforeseen significant liabilities or other unanticipated or unintended effects of such activities and the performance of National Grid’s subsidiaries. In addition National Grid’s reputation may be harmed if consumers of energy suffer a disruption to their supply. For a more detailed description of some of these assumptions, risks and uncertainties, together with any other risk factors, please see National Grid’s filings with and submissions to the US Securities and Exchange Commission (the SEC) (and in particular the Risk Factors and Operating and Financial Review sections in its most recent Annual Report on Form 20-F). The effects of these factors are difficult to predict. New factors emerge from time to time and National Grid cannot assess the potential impact of any such factor on its activities or the extent to which any factor, or combination of factors, may cause its results to differ materially from those contained in any forward-looking statement. Except as may be required by law or regulation, National Grid undertakes no obligation to update any of its forward-looking statements, which speak only as of the date of this announcement. The contents of any website references herein do not form part of this announcement.