National Grid Regulatory News (NG.)

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

National Grid PLC

1b. Please indicate if the issuer is a non-UK issuer (please mark with an "X" if appropriate)

Non-UK issuer

2. Reason for the notification (please mark the appropriate box or boxes with an "X")

An acquisition or disposal of voting rights

An acquisition or disposal of financial instruments

An event changing the breakdown of voting rights

Other (please specify): Extension of part of previously announced position. No threshold has been crossed. See Box 11 below.

X

3. Details of person subject to the notification obligationiv

Name

Competrol International Investments Limited

City and country of registered office (if applicable)

Tortola, British Virgin Islands

4. Full name of shareholder(s) (if different from 3.)v

Name

City and country of registered office (if applicable)

5. Date on which the threshold was crossed or reachedvi:

Part of existing position extended on 23 February 2018. No threshold has been crossed. See Box 11 below.

6. Date on which issuer notified (DD/MM/YYYY):

23/02/2018

7. Total positions of person(s) subject to the notification obligation

% of voting rights attached to shares (total of 8. A)

% of voting rights through financial instruments(total of 8.B 1 + 8.B 2)

Total of both in % (8.A + 8.B)

Total number of voting rights of issuervii

Resulting situation on the date on which threshold was crossed or reached

-

3.72

3.72

125,733,926

Position of previous notification (if

applicable)

-

3.65

3.65

8. Notified details of the resulting situation on the date on which the threshold was crossed or reachedviii

A: Voting rights attached to shares

Class/type ofshares

ISIN code (if possible)

Number of voting rightsix

% of voting rights

Direct

(Art 9 of Directive 2004/109/EC) (DTR5.1)

Indirect

(Art 10 of Directive 2004/109/EC) (DTR5.2.1)

Direct

(Art 9 of Directive 2004/109/EC) (DTR5.1)

Indirect

(Art 10 of Directive 2004/109/EC) (DTR5.2.1)

SUBTOTAL 8. A

B 1: Financial Instruments according to Art. 13(1)(a) of Directive 2004/109/EC (DTR5.3.1.1 (a))

Type of financial instrument

Expirationdatex

Exercise/Conversion Periodxi

Number of voting rights that may be acquired if the instrument is

exercised/converted.

% of voting rights

SUBTOTAL 8. B 1

B 2: Financial Instruments with similar economic effect according to Art. 13(1)(b) of Directive 2004/109/EC (DTR5.3.1.1 (b))

Type of financial instrument

Expirationdatex

Exercise/Conversion Period xi

Physical or cash

settlementxii

Number of voting rights

% of voting rights

Total Return Equity Swaps

27 February 2019

-

Cash

28,875,000

0.85

27 February 2020

-

Cash

96,858,926

2.87

SUBTOTAL 8.B.2

125,733,926

3.72

9. Information in relation to the person subject to the notification obligation (please mark the

applicable box with an "X")

Person subject to the notification obligation is not controlled by any natural person or legal entity and does not control any other undertaking(s) holding directly or indirectly an interest in the (underlying) issuerxiii

Full chain of controlled undertakings through which the voting rights and/or thefinancial instruments are effectively held starting with the ultimate controlling natural person or legal entityxiv (please add additional rows as necessary)

X

Namexv

% of voting rights if it equals or is higher than the notifiable threshold

% of voting rights through financial instruments if it equals or is higher than the notifiable threshold

Total of both if it equals or is higher than the notifiable threshold

Olayan Investments Company Establishment

-

3.72

3.72

Competrol Establishment

-

3.72

3.72

10. In case of proxy voting, please identify:

Name of the proxy holder

The number and % of voting rights held

The date until which the voting rights will be held

11. Additional informationxvi

This notification is merely as a result of the extension of part of the existing position to 27 February 2019. There has been no change to the aggregate number of shares referable to the aggregate position (other than as a result of the share consolidation effected in May 2017) and no threshold has been crossed. The change in the % of voting rights in Box 7 is as a result of the change to the total number of voting rights.

Place of completion

London, UK

Date of completion

23 February 2018