Costain Regulatory News (COST)

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARES

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

YES

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

JPMorgan Asset Management Holdings Inc.

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

JPMorgan Asset Management (UK) Limited

JPMorgan Asset Management (Taiwan) Limited

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

10 September 2015

6. Date on which issuer notified:

11 September 2015

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

5% Upwards

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

GB00B64NSP76

Below minimum threshold

Below minimum threshold

4,931,188

4.83%

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

Contract for Difference

171,598

Nominal

Delta

0.17%

Total (A+B+C)

Number of voting rights

Percentage of voting rights

5,102,786

5.00%

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

Total disclosable holding for JPMorgan Asset Management Holdings Inc : 5,102,786 (5.00%)

JPMorgan Asset Management (UK) Limited

JPMorgan Asset Management (Taiwan) Limited

Proxy Voting:

10. Name of the proxy holder:

N/A

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

N/A

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

N/A

13. Additional information:

N/A

14. Contact name:

Tung T Le

15. Contact telephone number:

020 7742 7272