Costain Regulatory News (COST)

NOTIFICATION OF MAJOR HOLDINGS (to be sent to the relevant issuer and to the FCA in Microsoft Word format if possible)i

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

COSTAIN GROUP 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

x

An acquisition or disposal of financial instruments

x

An event changing the breakdown of voting rights

Other (please specify)iii:

3. Details of person subject to the notification obligationiv

Name

GLG PARTNERS LP

City and country of registered office (if applicable)

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

Name

N/A

City and country of registered office (if applicable)

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

11/01/2019

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

14/01/2019

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

7.87

2.21

10.08

107,013,848

Position of previous notification (if

applicable)

4.01

1.08

5.09

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)

GB00B64NSP76

8,421,571

7.87

SUBTOTAL 8. A

8,421,571

7.87

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

CFD

2,366,067

2.21

SUBTOTAL 8.B.2

2,366,067

2.21

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

x

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)

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

10. In case of proxy voting, please identify:

Name of the proxy holder

Not Applicable

The number and % of voting rights held

Not Applicable

The date until which the voting rights will be held

Not Applicable

11. Additional informationxvi

Not Applicable

Place of completion

London

Date of completion

14/01/2019