SCHEDULE 13D/A 0001882923 XXXXXXXX LIVE 6 Ordinary Shares, par value $0.0025 per share 08/29/2025 false 0001859690 G0567U127 Arqit Quantum Inc.

1st Floor 3 Orchard Place London X0 SW1H 0BF

Heritage Assets SCSp 377 97 97 63 19 c/o Heritage Services SAM 7 rue du Gabian Monaco O9 98000 0001882923 N Heritage Assets SCSp AF N N4 0.00 10214252.00 0.00 10214252.00 10214252.00 N 46.0 OO (Rows 8, 10 and 11) On a post-Reverse Stock Split (as defined herein) basis. On September 19, 2024, Arqit Quantum Inc., a Cayman Islands exempted limited liability company ("Arqit"), announced the implementation of a reverse stock split whereby every 25 outstanding ordinary shares of Arqit were consolidated into one ordinary share, par value $0.0025 per share (the "Ordinary Shares") (such consolidation, the "Reverse Stock Split"). The Ordinary Shares began trading on the Nasdaq Capital Market on a post-Reverse Stock Split basis on September 25, 2024. The CUSIP of the Ordinary Shares following the Reverse Stock Split is G0567U127. 0001882928 N M Management S.A. AF N N4 0.00 10214252.00 0.00 10214252.00 10214252.00 N 46.0 OO (Rows 8, 10 and 11) On a post-Reverse Stock Split basis. The Ordinary Shares began trading on the Nasdaq Capital Market on a post-Reverse Stock Split basis on September 25, 2024. The CUSIP of the Ordinary Shares following the Reverse Stock Split is G0567U127. 0001840678 N Manfredi Lefebvre d'Ovidio AF N L6 0.00 10214252.00 0.00 10214252.00 10214252.00 N 46.0 IN (Rows 8, 10 and 11) On a post-Reverse Stock Split basis. The Ordinary Shares began trading on the Nasdaq Capital Market on a post-Reverse Stock Split basis on September 25, 2024. The CUSIP of the Ordinary Shares following the Reverse Stock Split is G0567U127. Ordinary Shares, par value $0.0025 per share Arqit Quantum Inc. 1st Floor 3 Orchard Place London X0 SW1H 0BF This Amendment No. 6 to Schedule 13D (this "Amendment No. 6") is being filed by Heritage Assets SCSp, a Luxembourg company, M Management S.A., a Luxembourg company, and Manfredi Lefebvre d'Ovidio (collectively, the "Reporting Persons"), with respect to the Ordinary Shares of Arqit Quantum Inc., a Cayman Islands exempted limited liability company ("Arqit" or the "Issuer"), to amend the Schedule 13D filed by the Reporting Persons on September 14, 2021 (as amended on December 9, 2021, September 15, 2023, October 2, 2024, May 29, 2025 and August 26, 2025, the "Schedule 13D"). The class of equity security to which this Amendment No. 6 relates is the Ordinary Shares, par value $0.0025 per share, of the Issuer. The address of the principal executive offices of the Issuer is 1st Floor, 3 Orchard Place, London SW1H 0BF, United Kingdom. Information given in response to each item shall be deemed incorporated by reference in all other items, as applicable. Item 3 of the Schedule 13D is amended by adding the information set forth in Item 4 of this Amendment No. 6. Item 4 of the Schedule 13D is amended by adding the following information: This Amendment No. 6 is being filed to update the aggregate number of Ordinary Shares and percentage of Ordinary Shares of Arqit beneficially owned by the Reporting Persons due to the dilution caused by Arqit's issuance of additional Ordinary Shares from time to time since the date of the filing of Amendment No. 5 to Schedule 13D by the Reporting Persons, with respect to the Ordinary Shares of Arqit, on August 26, 2025 ("Amendment No. 5"), which resulted in a decrease of over one percent (1%) in the aggregate percentage ownership reported by the Reporting Persons in Amendment No. 5. In addition, this Amendment No.6 contains information regarding the sale by the Reporting Persons of Business Combination Warrants (as defined in Arqit's Annual Report on Form 20-F for the fiscal year ended September 30, 2024, filed with the Securities and Exchange Commission (the "SEC") on December 5, 2024) at the average prices set forth in the table below, in each case on a post-Reverse Stock Split basis, in each case in open market transactions and as set forth in the table below. Date of Transaction Amount of Business Average Price per Combination Warrants Business Combination Warrant ($) 08/20/2025 272 7.3 08/21/2025 555 7.4 08/22/2025 5,223 6.7 08/25/2025 5,640 5.2 08/26/2025 960 5.1 08/27/2025 1,432 5.3 08/28/2025 11,903 4.2 08/29/2025 195 4.5 09/02/2025 131 4.6 09/03/2025 1,109 4.8 09/04/2025 5,672 3.6 09/05/2025 9,474 2.9 09/09/2025 480 4.2 09/11/2025 6,318 3.8 09/12/2025 2,490 3.9 09/15/2025 6,197 3.3 The responses of the Reporting Person with respect to Rows 7 through 13 of the respective cover pages of the individual Reporting Persons to this Amendment No. 6 are incorporated herein by reference. The Reporting Persons' aggregate percentage of beneficial ownership is approximately 46.0% of the outstanding Ordinary Shares. Calculations of the percentage of Ordinary Shares beneficially owned are based on 22,184,708 Ordinary Shares outstanding (including Ordinary Shares that the Reporting Persons have a right to acquire within 60 days) as of September 18, 2025, based on information included in the Issuer's prospectus supplement filed pursuant to Rule 424(b)(3) with the SEC on September 19, 2025. Except as set forth in this Amendment No. 6, none of the Reporting Persons has engaged in any transaction with respect to the Ordinary Shares since the date of the filing of Amendment No. 5. Not applicable. Not applicable. No material changes. Heritage Assets SCSp By: M Management S.A., its Sole Manager and General Partner /s/ Manfredi Lefebvre d'Ovidio 09/24/2025 By: M Management S.A., its Sole Manager and General Partner /s/ Giorgio Scelsi 09/24/2025 M Management S.A. /s/ Manfredi Lefebvre d'Ovidio 09/24/2025 /s/ Giorgio Scelsi 09/24/2025 Manfredi Lefebvre d'Ovidio /s/ Manfredi Lefebvre d'Ovidio 09/24/2025