Announcement PDF RNS Number : 2028Z Mendell Helium PLC 15 October 2026 TR-1: Standard form for notification of major holdings 1. Issuer Details ISIN GB00BLD3FF28 Issuer Name MENDELL HELIUM PLC UK or Non-UK Issuer UK 2. Reason for Notification An event changing the breakdown of voting rights 3. Details of person subject to the notification obligation Name Premier Miton Group plc City of registered office (if applicable) London Country of registered office (if applicable) United Kingdom 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 15-Oct-2026 6. Date on which Issuer notified 15-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 12.921074 0.000000 12.921074 46248517 Position of previous notification (if applicable) 13.879197 0.000000 13.879197 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) GB00BLD3FF28 46248517 12.921074 Sub Total 8.A 46248517 12.921074% 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 Sub Total 8.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 than the notifiable threshold Total of both if it equals or is higher than the notifiable threshold Premier Miton Group plc Premier Miton Group Plc Premier Miton Group plc Premier Asset Management Midco Ltd Premier Miton Group plc Premier Asset Management Holdings Ltd Premier Miton Group plc Premier Asset Management Limited Premier Miton Group plc Premier Investment Group Ltd Premier Miton Group plc Premier Fund Managers Ltd 12.921074 12.921074% 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 15-Oct-2026 13. Place Of Completion Guildford, UK 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 HOLEAKESFSPKFFA