Holding(s) in Company

1. Identity of the issuer or the underlying issuer of existing shares to which voting rights are attached: ii

National Grid plc

2 Reason for the notification (please tick the appropriate box or boxes):

An acquisition or disposal of voting rights

An acquisition or disposal of qualifying financial instruments which may result in the acquisition of shares already issued to which voting rights are attached

An acquisition or disposal of instruments with similar economic effect to qualifying financial instruments

An event changing the breakdown of voting rights

Other (please specify):

Extension of previously announced position. See Box 13 below. No threshold has been crossed.

X

3. Full name of person(s) subject to the notification obligation: iii

Competrol International Investments Limited

4. Full name of shareholder(s)

(if different from 3.): iv

5. Date of the transaction and date on which the threshold is crossed or reached: v

Existing position extended on 23 February 2017. See Box 13 below. No threshold was crossed.

6. Date on which issuer notified:

23 February 2017

7. Threshold(s) that is/are crossed or

reached: vi, vii

8. Notified details:

A: Voting rights attached to shares viii, ix

Class/type ofshares

if possible usingthe ISIN CODE

Situation previousto the triggeringtransaction

Resulting situation after the triggering transaction

NumberofShares

NumberofVotingRights

Numberof shares

Number of votingrights

% of voting rights x

Direct

Direct xi

Indirect xii

Direct

Indirect

B: Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Expirationdate xiii

Exercise/ConversionPeriod xiv

Number of votingrights that may beacquired if theinstrument isexercised/ converted.

% of votingrights

C: Financial Instruments with similar economic effect to Qualifying Financial Instruments xv, xvi

Resulting situation after the triggering transaction

Type of financialinstrument

Exerciseprice

Expirationdate xvii

Exercise/Conversionperiod xviii

Number of votingrights instrumentrefers to

% of voting rights xix, xx

Total Return Equity Swaps

-

27 February 2018

-

31,500,000

Nominal

Delta

-

0.84

-

27 February 2020

-

105,664,285

-

2.81

Total

137,164,285

-

3.65

Total (A+B+C)

Number of voting rights

Percentage of voting rights

137,164,285

3.65

9. Chain of controlled undertakings through which the voting rights and/or thefinancial instruments are effectively held, if applicable: xxi

Proxy Voting:

10. Name of the proxy holder:

 N/A

11. Number of voting rights proxy holder will cease to hold:

 N/A

12. Date on which proxy holder will cease to hold voting rights:

 N/A

13. Additional information:

This notification is merely as a result of the extension of part of an existing position to 27 February 2018 and the extension of the remainder of the existing position to 27 February 2020. There has been no change to the aggregate number of shares referable to the aggregate position and no threshold has been crossed.

14. Contact name:

Struan Oliver, Sidley Austin LLP

15. Contact telephone number:

020 7360 2063