Transaction in Own Shares

Summary by AI ^BETAClose X

Costain Group PLC has purchased a total of 262,115 ordinary shares between April 15 and April 21, 2026, as part of its share buyback program. The weighted average purchase price during this period ranged from 186.08 pence to 195.91 pence per share. These shares are intended for cancellation, and following this, the company's total issued ordinary shares will be 268,417,436. The aggregate volume of shares purchased across various trading venues during this period was 221,615, with a volume-weighted average price of 189.27 pence.

Disclaimer*

Costain Group PLC

22 April 2026

Costain Group PLC

Transaction in own shares

Costain Group PLC ("Costain") announces that, in accordance with the terms of its share buyback programme (the "Programme") announced on 10 March 2026, it has purchased the following number of its ordinary shares of 1 pence each ("Ordinary Shares") on the London Stock Exchange through Panmure Liberum in the period from 15 April 2026 to 21 April 2026.

Date of Purchase	Number of ordinary shares purchased	Weighted average price per day (pence)	Highest price per share (pence)	Lowest price per share (pence)
15 April 2026	45,000	195.91	199.40	192.40
16 April 2026	59,966	189.45	192.40	187.60
20 April 2026	60,000	188.02	189.40	186.40
21 April 2026	57,149	186.08	188.40	184.20

The Company intends to cancel the purchased shares. The Company does not hold any ordinary shares in treasury.

Costain has now purchased 1,297,459 Ordinary Shares in aggregate for cancellation under the Buyback Programme. Following settlement of the above purchases and cancellation of the purchased Ordinary Shares, the Group's total number of Ordinary Shares in issue will be 268,417,436 Ordinary Shares.

In accordance with Article 5(1)(b) of Market Abuse Regulation (EU) No 596/2014 (as it forms part of the law of the United Kingdom by virtue of the European Union (Withdrawal) Act 2018, as implemented, retained, amended, extended, re-enacted or otherwise given effect in the United Kingdom from 1 January 2021 and as amended or supplemented in the United Kingdom thereafter) a full breakdown of the individual trades made by Panmure Liberum on behalf of the Company as part of the Programme can be found at:

http://www.rns-pdf.londonstockexchange.com/rns/5201B_1-2026-4-22.pdf

Aggregate information:

Venue	Volume-weighted average price (pence per share)	Aggregated volume	Lowest price per share (pence per share)	Highest price per share (pence per share)
BATE	189.03	87,600	184.20	198.60
XLON	189.83	118,399	184.20	199.40
CHIX	189.86	11,250	185.00	199.20
TRQX	189.37	4,866	184.40	198.80

Enquiries:

Investors and analysts

Matt Jones, Costain

Matt.Jones@costain.com

+44 (0) 7860 922 341

Financial media - Headland

Andy Rivett-Carnac

Charlie Twigg

costain@headlandconsultancy.com

+44 (0) 7968 997365

+44 (0) 7946 494568

This information is provided by RNS, the news service of the London Stock Exchange. RNS is approved by the Financial Conduct Authority to act as a Primary Information Provider in the United Kingdom. Terms and conditions relating to the use and distribution of this information may apply. For further information, please contact rns@lseg.com or visit www.rns.com.

RNS may use your IP address to confirm compliance with the terms and conditions, to analyse how you engage with the information contained in this communication, and to share such analysis on an anonymised basis with others as part of our commercial services. For further information about how RNS and the London Stock Exchange use the personal data you provide us, please see our Privacy Policy.

END