REG — Diploma PLC — Holding(s) in Company

For best results when printing this announcement, please click on link below: RNS Number: 3953V Diploma PLC 18 September 2026 10-11 CHARTERHOUSE SQUARE, LONDON EC1M 6EE TELEPHONE: +44 (0)20 7549 5700 18 September 2026 TR-1: Standard form for notification of major holdings 1. Issuer Details ISIN GB0001826634 Issuer Name DIPLOMA 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 The Capital Group Companies, Inc.

City of registered office (if applicable) Los Angeles Country of registered office (if applicable) USA 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 11-Sep-2026 6. Date on which Issuer notified 14-Sep-2026 7.

152920 8. Notified details of the resulting situation on the date on which the threshold was crossed or reached 8A. 817392% 8B1. B1 8B2.

B2 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 Total of both if it equals or is higher than the notifiable threshold than the notifiable threshold The Capital Group Companies, Inc.

655713% The Capital Group Companies, Inc. Capital International Limited The Capital Group Companies, Inc. Capital International Sarl The Capital Group Companies, Inc. Capital International, Inc.

The Capital Group Companies, Inc. SMALLCAP World Fund, Inc. 720077% Management Company) 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 The Capital Group Companies, Inc. ("CGC") is the parent company of Capital Research and Management Company ("CRMC") and Capital Bank & Trust Company ("CB&T"). -based investment management company that serves as investment manager to the American Funds family of mutual funds, other pooled investment vehicles, as well as individual and institutional clients. CRMC and its investment manager affiliates manage equity assets for various investment companies through three divisions, Capital Research Global Investors, Capital International Investors and Capital World Investors.

CRMC is the parent company of Capital Group International, Inc. , Capital Group Private Client Services Inc, and Capital Group Investment Management Private Limited. CGII management companies primarily serve as investment managers to institutional and high net worth clients. -based registered investment adviser and an affiliated federally chartered bank.

Neither CGC nor any of its affiliates own shares of the Issuer for its own account. Rather, the shares reported on this Notification are owned by accounts under the discretionary investment management of one or more of the investment management companies described above. 12. Date of Completion 14-Sep-2026 13.

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