Holding(s) in Company

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARESi

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

Costain Group PLC

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

An acquisition or disposal of voting rights

X

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):

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

Mohammed Abdulmohsin Al-Kharafi & Sons Company for General Trading, General Contracting and Industrial Structures WLL

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

BBHISL Nominees Limited (designation 125688)

5. Date of the transaction and date onwhich the threshold is crossed orreached: v

16 March 2015

6. Date on which issuer notified:

16 March 2015

7. Threshold(s) that is/are crossed orreached: vi, vii

10%, 9% and 8%

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

ORD 50p SHARES

GB00B64NSP76

10,429,490

10,429,490

7,339,490

7,339,490

7.25%

B: Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Expirationdate xiii

Exercise/Conversion Period 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

Exercise price

Expiration date xvii

Exercise/Conversion period xviii

Number of voting rights instrument refers to

% of voting rights xix, xx

Nominal

Delta

Total (A+B+C)

Number of voting rights

Percentage of voting rights

7,339,490

7.25%

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:

11. Number of voting rights proxy holder will ceaseto hold:

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

13. Additional information:

(a) In accordance with DTR 3.1.2R, Mohammed Abdulmohsin Al-Kharafi & Sons Company for General Trading, General Contracting and Industrial Structures WLL are deemed to be a connected person of Mr Ahmed Samy, a non-executive director of Costain Group PLC

(b) 3,090,000 shares were sold at 305p per share

 (c) The transaction was carried out in London

14. Contact name:

Ahmed Samy

15. Contact telephone number:

+(965)-2483 0025