Costain Group PlcLSE: COST

Holding(s) in Company

· Issued by Costain Group Plc

TR-1: Standard form for notification of major holdings

1. Issuer Details

ISIN

GB00B64NSP76

Issuer Name

COSTAIN GROUP PLC

UK or Non-UK Issuer

UK

2. Reason for Notification

An acquisition or disposal of voting rights

3. Details of person subject to the notification obligation

Name

FIL Limited

City of registered office (if applicable)

Hamilton

Country of registered office (if applicable)

Bermuda

4. Details of the shareholder

Full name of shareholder(s) if different from the person(s) subject to the notification obligation, above

City of registered office (if applicable)

Country of registered office (if applicable)

5. Date on which the threshold was crossed or reached

02-Oct-2026

6. Date on which Issuer notified

06-Oct-2026

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 held in issuer

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

8.717800

2.227200

10.945000

28711458

Position of previous notification (if applicable)

9.295100

1.922200

11.217300

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

8A. Voting rights attached to shares

Class/Type of shares ISIN code(if possible)

Number of direct voting rights (DTR5.1)

Number of indirect voting rights (DTR5.2.1)

% of direct voting rights (DTR5.1)

% of indirect voting rights (DTR5.2.1)

GB00B64NSP76

22868900

8.717800

Sub Total 8.A

22868900

8.717800%

8B1. Financial Instruments according to (DTR5.3.1R.(1) (a))

Type of financial instrument

Expiration date

Exercise/conversion period

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

% of voting rights

Sub Total 8.B1

8B2. Financial Instruments with similar economic effect according to (DTR5.3.1R.(1) (b))

Type of financial instrument

Expiration date

Exercise/conversion period

Physical or cash settlement

Number of voting rights

% of voting rights

CFD

Cash

5842558

2.227200

Sub Total 8.B2

5842558

2.227200%

9. Information in relation to the person subject to the notification obligation

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

Ultimate controlling person

Name of controlled undertaking

% 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

FIL Limited

FIL Limited

8.717800

2.227200

10.945000%

FIL Limited

FIL Financial Services Holdings Limited

8.717800

2.227200

10.945000%

FIL Limited

FIL Financial Services Holdings 2 Limited

8.717800

2.227200

10.945000%

FIL Limited

FIL Holdings (UK) Limited

8.717800

2.227200

10.945000%

FIL Limited

FIL Investments International

8.717800

2.227200

10.945000%

10. In case of proxy voting

Name of the proxy holder

The number and % of voting rights held

The date until which the voting rights will be held

If date does not apply, explain below

11. Additional Information

12. Date of Completion

06-Oct-2026

13. Place Of Completion

Dublin, Ireland

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