Filed Pursuant to Rule 424(b)(3)

Registration No. 333-259982

Supplement No. 1

(To Prospectus dated December 23, 2021)

Arqit Quantum Inc.

117,925,000 Ordinary Shares

6,266,667 Warrants to Purchase Ordinary Shares

14,891,640 Ordinary Shares Underlying Warrants

This prospectus supplement updates and amends certain information contained in the prospectus dated December 23, 2021 (the “Prospectus”) covering the offer and sale from time to time by the selling securityholders named in the Prospectus of up to 117,925,000 of our ordinary shares, par value $0.0001 per share (“Ordinary Shares”), and warrants to purchase up to 6,266,667 Ordinary Shares. The Prospectus also relates to the issuance by us of up to 14,891,640 Ordinary Shares, that are issuable by us upon the exercise of the Public Warrants (as defined in the Prospectus), which were previously registered, and the Private Warrants (as defined in the Prospectus). You should read this supplement no. 1 in conjunction with the Prospectus. This prospectus supplement is not complete without, and may not be utilized except in connection with, the Prospectus, including any amendments or supplements thereto.

Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” beginning on page 8 of the Prospectus, and under similar headings in any amendment or supplements to the Prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of the Prospectus or this prospectus supplement. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is May 12, 2022

EXPLANATORY NOTE

This prospectus supplement updates and supplements the Prospectus to (i) update the table of Selling Securityholders (as defined in the Prospectus) to reflect certain sales and distributions that have been made as permitted under the “Plan of Distribution” included in the Prospectus, and (ii) provide the disclosure regarding amendments to extend the Lock-Up Agreements (as defined below) and financial statements tables for the six months ended March 31, 2022 that were contained in our report of foreign private issuer on Form 6-K, furnished to the Securities and Exchange Commission on May 12, 2022.

Extension of Lock-up Agreements

In connection with the business combination among Centricus Acquisition Corp., Arqit Limited and us, which closed on September 3, 2021 (the “Business Combination”), we entered into lock-up agreements with Centricus Heritage, LLC (the “Sponsor”) and the former shareholders of Arqit Limited (the “Arqit Limited Shareholders”), which were amended and restated on October 4, 2021 (the “Lock-Up Agreements”).

Pursuant to the Lock-Up Agreements, the Sponsor and the Arqit Limited Shareholders (and their transferees) had agreed not to transfer any Ordinary Shares received pursuant to the Business Combination during the period commencing from the date of the closing of the Business Combination until the earlier to occur of (i) 11:59 p.m. Eastern time on the close of trading on the second full trading day following the public dissemination by us of our financial results for the six months ended March 31, 2022 by press release to the national wire services or by making a filing with the SEC; and (ii) such time as determined by our board of directors as being in the best interest of the parties to permit transfers.

On May 11, 2022, the majority of the former members of the Sponsor and the Arqit Limited Shareholders (or their transferees), agreed to amend the Lock-Up Agreements (the “Extensions”), and have agreed not to transfer any Ordinary Shares received pursuant to the Business Combination during the period commencing from the date of the Extensions until the earlier to occur of (i) September 3, 2022 and (ii) such time as determined by our board of directors as being in the best interest of the parties to permit transfers, in whole or in part.

All of the shareholders approached regarding lock-up extensions (holding 105,886,259 of the 108,585,000 shares subject to the Lock-Up Agreements) agreed to extend their lock-up agreements.

Condensed consolidated interim financial statements for the period ended 31 March 2022

Arqit Quantum Inc.  

Condensed Consolidated Statement of Comprehensive Income 

For the period ended 31 March 2022

All of the Group’s activities were derived from continuing operations during the above financial periods.

Arqit Quantum Inc. 

Condensed Consolidated Statement of Financial Position 

As at 31 March 2022

Arqit Quantum Inc. 

Condensed Consolidated Statement of Cash Flows 

For the period ended 31 March 2022