PRICING ANNOUNCEMENT

NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION, IN WHOLE OR IN PART, DIRECTLY OR INDIRECTLY, IN OR INTO THE UNITED STATES, AUSTRALIA, CANADA, JAPAN OR SOUTH AFRICA OR ANY OTHER JURISDICTION WHERE SUCH RELEASE, PUBLICATION OR DISTRIBUTION WOULD BE UNLAWFUL. FURTHER, THIS ANNOUNCEMENT IS FOR INFORMATION PURPOSES ONLY AND IS NOT AN OFFER OF SECURITIES IN ANY JURISDICTION.

THIS ANNOUNCEMENT CONTAINS INSIDE INFORMATION.

RESULTS OF PLACING IN Costain Group Plc (THE "COMPANY")

 11^th September 2024

Further to the announcement released on 10^th September 2024, ASGC Construction L.L.C. (the "Seller") announces that it has sold an aggregate of 41,666,666 ordinary shares of 1 pence each in the capital of the Company (the "Placing Shares") at a price of 91 pence per share (the "Placing Price") through a placing to institutional investors (the "Placing"). The Placing Shares represent approximately 14.97% of the Company's issued ordinary share capital. On the back of strong deal momentum, the Placing was upsized by approximately 39% from the original Placing size of 30 million ordinary shares (as announced 10 September 2024)

The aggregate gross sale proceeds raised through the Placing are approximately £37.9m.This represents a full exit by ASGC Construction L.L.C. of its position in the Company.

The Company is not party to the Placing and will not receive any proceeds from the Placing.

The proceeds of the Placing are payable in cash on usual settlement terms, and closing of the Placing is expected to occur on a T+2 basis on 13th September 2024, subject to the satisfaction or waiver of certain customary conditions.

Following its exit ASGC Construction L.L.C. will not be subject to the lock-up obligation announced on 10 September 2024.

Redburn (Europe) Limited ("Redburn Atlantic") is acting as sole bookrunner in connection with the Placing (the "Manager").

The Placing Shares rank pari passu in all respects with the Company's voting ordinary shares.

For further information, please contact:

Redburn Atlantic                              

Aisling Meany/ Aisling.Meany@redburnatlantic.com / +44 20 7000 2002

Ben Glaeser / Ben.Glaeser@redburnatlantic.com / +44 20 7000 2015

IMPORTANT NOTICES

THIS ANNOUNCEMENT IS RESTRICTED AND IS NOT FOR PUBLICATION, RELEASE, TRANSMISSION, FORWARDING OR DISTRIBUTION, DIRECTLY OR INDIRECTLY, IN WHOLE OR IN PART, IN OR INTO THE UNITED STATES OF AMERICA, ITS TERRITORIES AND POSSESSIONS, ANY STATE OF THE UNITED STATES OR THE DISTRICT OF COLUMBIA (COLLECTIVELY, THE "UNITED STATES"), AUSTRALIA, CANADA, JAPAN OR SOUTH AFRICA OR ANY OTHER JURISDICTION IN WHICH SUCH PUBLICATION, RELEASE OR DISTRIBUTION WOULD BE UNLAWFUL. FURTHER, THIS ANNOUNCEMENT IS FOR INFORMATION PURPOSES ONLY AND IS NOT AN OFFER OF SECURITIES IN ANY JURISDICTION.

This Announcement or any part of it does not constitute or form part of any offer to issue or sell, or the solicitation of an offer to acquire, purchase or subscribe for, any securities in the United States, Australia, Canada, Japan or South Africa or any other jurisdiction in which the same would be unlawful. No public offering of the Placing Shares is being made in any such jurisdiction.

No action has been taken by the Seller, Redburn Atlantic or any of their respective affiliates, or any person acting on its or their behalf that would permit an offer of the Placing Shares or possession or distribution of this Announcement or any other offering or publicity material relating to such Placing Shares in any jurisdiction where action for that purpose is required. Persons into whose possession this Announcement comes are required by the Seller and Redburn Atlantic to inform themselves about, and to observe, such restrictions.

No prospectus, offering memorandum, offering document or admission document has been or will be made available in connection with the matters contained in this Announcement and no such prospectus is required (in accordance with Regulation (EU) No 2017/1129 (as amended) (the "EU Prospectus Regulation") or the EU Prospectus Regulation as it forms part of UK domestic law by virtue of the European Union (Withdrawal) Act 2018 (the "UK Prospectus Regulation")) to be published. Persons needing advice should consult a qualified independent legal adviser, business adviser, financial adviser or tax adviser for legal, financial, business or tax advice.

The securities referred to herein have not been and will not be registered under the US Securities Act of 1933, as amended (the "Securities Act"), or with any securities regulatory authority of any State or other jurisdiction of the United States, and may not be offered, sold or transferred, directly or indirectly, in or into the United States except pursuant to an exemption from, or in a transaction not subject to, the registration requirements of the Securities Act and in compliance with the securities laws of any State or any other jurisdiction of the United States. Accordingly, the Placing Shares have been offered and sold  outside of the United States in "offshore transactions" (as such term is defined in Regulation S under the Securities Act ("Regulation S")) pursuant to Regulation S and otherwise in accordance with applicable laws. No public offering of the Securities has been or will be made in the United States or elsewhere.

The Placing has not been approved or disapproved by the US Securities and Exchange Commission, any state securities commission in the United States or any US regulatory authority, nor have any of the foregoing authorities passed upon or endorsed the merits of the Placing, or the accuracy or adequacy of this presentation. Any representation to the contrary is a criminal offence in the United States.

This Announcement has not been approved by the Financial Conduct Authority (the "FCA") or the London Stock Exchange.

Members of the public were not eligible to take part in the Placing. This Announcement is directed at and is only being distributed to: (a) if in a member state of the European Economic Area (the "EEA"), qualified investors ("Qualified Investors") within the meaning of Article 2(e) of the EU Prospectus Regulation; (b) if in the United Kingdom, qualified investors within the meaning of Article 2(e) of the UK Prospectus Regulation who are also (i) persons having professional experience in matters relating to investments who fall within the definition of "investment professional" in Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended (the "Order"); or (ii) high net worth companies, unincorporated associations and partnerships and trustees of high value trusts as described in Article 49(2)(a) to (d) of the Order ("UK Qualified Investors"); or (c) other persons to whom it may otherwise be lawfully communicated (all such persons together being "Relevant Persons"). This Announcement must not be acted on or relied on by persons who are not Relevant Persons. Any investment or investment activity to which this Announcement relates is available only to Relevant Persons and will be engaged in only with Relevant Persons.

Certain statements contained in this Announcement may constitute "forward-looking statements". Words such as "believes", "anticipates", "estimates", "expects", "intends", "plans", "aims", "potential", "will", "would", "could", "considered", "likely", "estimate" and variations of these words and similar future or conditional expressions, are intended to identify forward-looking statements but are not the exclusive means of identifying such statements. These statements and forecasts involve risk and uncertainty because they relate to events and depend upon future circumstances that have not occurred. There are a number of factors that could cause actual results or developments to differ materially from those expressed or implied by these forward-looking statements and forecasts. No representation or warranty is made as to the achievement or reasonableness of, and no reliance should be placed on, such forward-looking statements. The forward-looking statements contained in this Announcement speak only as of the date of this Announcement. The Seller, Redburn Atlantic, their respective affiliates and any person acting on their behalf each expressly disclaim any obligation or undertaking to update or revise publicly any forward-looking statements, whether as a result of new information, future events or otherwise, unless required to do so by applicable law or regulation, the FCA or the London Stock Exchange.

Redburn Atlantic is authorised and regulated in the United Kingdom by the FCA. Redburn Atlantic is acting exclusively for the Seller and no one else in connection with the Placing, the contents of this Announcement or any other matters described in this Announcement. Redburn Atlantic will not regard any other person as its client in relation to the Placing, the content of this Announcement or any other matters described in this Announcement and will not be responsible to anyone other than the Seller for providing the protections afforded to its clients or for providing advice to any other person in relation to the Placing, the content of this Announcement or any other matters referred to in this Announcement.

This Announcement has been issued by and is the sole responsibility of the Seller. No representation or warranty, express or implied, is or will be made as to, or in relation to, and no responsibility or liability is or will be accepted by Redburn Atlantic or by any of its affiliates or any person acting on its or their behalf as to, or in relation to, the accuracy or completeness of this Announcement or any other written or oral information made available to or publicly available to any interested party or its advisers, and any liability therefore is expressly disclaimed.

This Announcement does not constitute a recommendation concerning any investor's investment decision with respect to the Placing. Any indication in this Announcement of the price at which ordinary shares have been bought or sold in the past cannot be relied upon as a guide to future performance. The price of shares and any income expected from them may go down as well as up and investors may not get back the full amount invested upon disposal of the shares. Past performance is no guide to future performance. This Announcement does not identify or suggest, or purport to identify or suggest, the risks (direct or indirect) that may be associated with an investment in the Placing Shares. The contents of this Announcement are not to be construed as legal, business, financial or tax advice. Each investor or prospective investor should consult their or its own legal adviser, business adviser, financial adviser or tax adviser for legal, financial, business or tax advice.

This Announcement has been prepared for the purposes of complying with applicable law and regulation in the United Kingdom and the information disclosed may not be the same as that which would have been disclosed if this Announcement had been prepared in accordance with the laws and regulations of any jurisdiction outside the United Kingdom.