SCHEDULE 13D/A 0001882923 XXXXXXXX LIVE 5 Ordinary Shares, par value $0.0025 per share 08/01/2025 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 Gabi Monaco O9 98000 0001882923 N Heritage Assets SCSp AF N N4 0.00 10273245.00 0.00 10273245.00 10273245.00 N 49.6 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 10273245.00 0.00 10273245.00 10273245.00 N 49.6 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 10273245.00 0.00 10273245.00 10273245.00 N 49.6 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. 5 to Schedule 13D (this "Amendment No. 5") 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 and May 29, 2025, the "Schedule 13D"). The class of equity security to which this Amendment No. 5 relates is the Ordinary Shares, par value $0.0025 per share, of the Issuer. The address of the principal executive offices of the Issuer is 1st Floor, 3 Orchard Place, London SW1H 0BF, United Kingdom. Information given in response to each item shall be deemed incorporated by reference in all other items, as applicable. Item 3 of the Schedule 13D is amended by adding the information set forth in Item 4 of this Amendment No. 5. Item 4 of the Schedule 13D is amended by adding the following information: This Amendment No. 5 is being filed to update the aggregate number of Ordinary Shares and percentage of Ordinary Shares of Arqit beneficially owned by the Reporting Persons (a) due to the sale by the Reporting Persons of Business Combination Warrants (as defined in Arqit's Annual Report on Form 20-F for the fiscal year ended September 30, 2024, filed with the Securities and Exchange Commission (the "SEC") on December 5, 2024) at the average prices set forth in the table below, in each case on a post-Reverse Stock Split basis, in each case in open market transactions and as set forth in the table below; and (b) because on August 1, 2025, warrants of Arqit to purchase up to 4,600,000 Ordinary Shares, which Heritage Assets SCSp purchased from Arqit in a private placement transaction pursuant to a securities purchase agreement, dated September 30, 2024 (the "September 2024 Warrants"), became exercisable within 60 days, which resulted in an increase of over one percent (1%) in the aggregate percentage ownership reported by the Reporting Persons in Amendment No. 4 to Schedule 13D, with respect to the Ordinary Shares of Arqit, which was filed by the Reporting Persons on May 29, 2025. Certain terms of the September 2024 Warrants are set forth in Amendment No. 3 to Schedule 13D, with respect to the Ordinary Shares of Arqit, which was filed by the Reporting Persons on October 2, 2024. Date of Transaction Amount of Business Average Price per Combination Warrants Business Combination Warrant ($) 05/28/2025 266 69.4 05/29/2025 182 63.4 05/30/2025 402 62.7 06/02/2025 1 62.5 06/04/2025 2,737 45.3 06/05/2025 1,409 46.4 06/06/2025 1,694 49.1 06/09/2025 1,147 45.3 06/10/2025 768 43.3 06/11/2025 1,632 45.6 06/12/2025 754 43.3 06/13/2025 404 41.3 06/16/2025 4,104 41.2 06/17/2025 6,005 39.1 06/18/2025 5,544 37.8 06/20/2025 6,333 33.9 06/23/2025 3,722 31.8 06/24/2025 11,038 31.4 06/25/2025 3,101 28.2 06/26/2025 8,587 27.2 06/27/2025 1,507 26.3 07/07/2025 932 25.0 07/08/2025 96 25.1 07/09/2025 1,709 25.1 07/10/2025 740 25.2 07/18/2025 132 25.0 07/21/2025 275 21.8 07/22/2025 1,247 19.5 07/23/2025 922 18.9 07/24/2025 714 18.3 07/25/2025 15,621 15.6 07/28/2025 12,570 8.5 07/29/2025 303 7.8 07/30/2025 1,578 9.1 07/31/2025 761 10.3 08/01/2025 712 10.3 08/04/2025 532 11.5 08/05/2025 420 9.8 08/06/2025 326 9.0 08/07/2025 155 9.1 08/08/2025 307 9.2 08/11/2025 419 8.6 08/12/2025 384 8.7 08/13/2025 363 8.2 08/14/2025 326 7.8 08/15/2025 127 8.0 08/18/2025 801 8.0 08/19/2025 142 7.6 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. 5 are incorporated herein by reference. The Reporting Persons' aggregate percentage of beneficial ownership is approximately 49.6% of the outstanding Ordinary Shares. Calculations of the percentage of Ordinary Shares beneficially owned are based on (i) 16,130,473 Ordinary Shares outstanding (including Ordinary Shares that the Reporting Persons have a right to acquire within 60 days) as of May 16, 2025, based on information included in the Issuer's prospectus supplement filed pursuant to Rule 424(b)(3) with the SEC on May 22, 2025, and (ii) 4,600,000 Ordinary Shares that the Reporting Persons have a right to acquire, in relation with the September 2024 Warrants as set forth in Item 4 of this Amendment No. 5, within 60 days as of August 1, 2025. Except as set forth in this Amendment No. 5, none of the Reporting Persons has engaged in any transaction with respect to the Ordinary Shares during the 60 days prior to the date of filing of this 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 08/26/2025 By: M Management S.A., its Sole Manager and General Partner /s/ Giorgio Scelsi 08/26/2025 M Management S.A. /s/ Manfredi Lefebvre d'Ovidio 08/26/2025 /s/ Giorgio Scelsi 08/26/2025 Manfredi Lefebvre d'Ovidio /s/ Manfredi Lefebvre d'Ovidio 08/26/2025