Subsequent Events	12 Months Ended
Dec. 31, 2022
Subsequent Events [Abstract]
Subsequent Events	19. Subsequent events Ratio change On February 10, 2023, the Company announced that the Company's Board of Directors approved a change to the ratio of the Company's ADSs to ordinary shares (the "ADS Ratio") from the previous ADS Ratio of one ADS to one ordinary share to a new ADS Ratio of one ADS to ten ordinary shares. The ratio change became effective on March 10, 2023. The change in the ADS Ratio had the same effect as a one-for-ten reverse ADS split and is intended to enable the Company to regain compliance with the Nasdaq minimum bid price requirement. As all financial statement and disclosure information is presented in ordinary share amounts, not ADSs, there was no impact to the consolidated financial statements and footnote disclosures. Issuance of shares through 2023 Private Placement On March 6, 2023, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) pursuant to which the Company agreed to sell, in an unregistered offering, up to an aggregate of (i) 99,166,900 shares, consisting of a combination of Ordinary Shares, nominal value £0.10 per share (“Ordinary Shares”) and Non-Voting Ordinary Shares, nominal value £0.10 per share (“Non-Voting Ordinary Shares” and together with the Ordinary Shares, “Shares”) and (ii) warrants to purchase an aggregate of 109,083,590 Ordinary Shares or Non-Voting Ordinary Shares (the “Warrants”). The 2023 Private Placement consists of two closings. The Company agreed to sell and issue in the initial closing of the 2023 Private Placement (i) 56,666,900 Shares and (ii) Warrants to purchase an aggregate of 62,333,590 Shares, at a purchase price of $6.00 per unit, where each unit consists of ten (10) Shares and an accompanying Warrant to purchase eleven (11) Shares. The initial closing of the 2023 Private Placement occurred on March 10, 2023. The Company received gross proceeds of approximately $34.0 million from the initial closing of the 2023 Private Placement, before deducting fees to the placement agent and other offering expenses payable by the Company. In addition, the Company agreed to sell and issue in the second closing of the 2023 Private Placement (i) 42,500,000 Shares and (ii) Warrants to purchase an aggregate of 46,750,000 Shares, at a purchase price of $8.00 per unit, where each unit consists of ten (10) Shares and an accompanying Warrant to purchase eleven (11) Shares. The second closing is conditioned upon (x) the Company’s announcement of its intention to file a biologics license application (“BLA”) submission following receipt of the minutes from the U.S. Food and Drug Administration (“FDA”) in connection with the Company’s pre-BLA (Type B) meeting for OTL-200, provided such minutes do not expressly advise the Company not to proceed with a BLA submission, and (y) receipt of Shareholder Approval (as defined below) (collectively, the “Second Closing Trigger”). In connection with the Private Placement, the Company has agreed to hold a meeting of its shareholders no later than 120 days following the initial closing of the Private Placement to seek approval to give the Company’s directors authority under s551 Companies Act 2006 to issue the securities to be issued and sold in the second closing of the Private Placement and the Shares issuable upon exercise of the Warrants to be issued and sold in the Private Placement, and to disapply pre-emption rights in respect of such authority under s570 of the Companies Act 2006 (collectively, “Shareholder Approval”). The second closing is expected to occur on the fifth trading day after the Company notifies the purchasing parties that the Second Closing Trigger has occurred and is subject to additional, customary closing conditions. If the Second Closing Trigger occurs, the Company anticipates receiving gross proceeds of approximately $34.0 million from the second closing of the 2023 Private Placement, before deducting fees to the placement agent and other offering expenses payable by the Company. Each Warrant will have an exercise price equal to $1.10 per Share in the event the Vesting Event (as defined below) occurs on or prior to December 31, 2024, and $0.95 per Share in the event the Vesting Event occurs after December 31, 2024. The Warrants will be exercisable during the 30 days following the Company’s announcement of receipt of marketing approval of its BLA with respect to OTL-200 (the “Vesting Event”); provided that exercise of any Warrant is conditioned upon the receipt of Shareholder Approval. Commencement of the 30-day exercise period may be delayed as set forth in the Warrants in the event the Vesting Event occurs prior to Shareholder Approval. The Warrants will expire at the conclusion of the 30-day exercise period or, if the Vesting Event does not occur, March 10, 2026.

Subsequent Events

12 Months Ended

Dec. 31, 2022

19. Subsequent events

Ratio change

On February 10, 2023, the Company announced that the Company's Board of Directors approved a change to the ratio of the Company's ADSs to ordinary shares (the "ADS Ratio") from the previous ADS Ratio of one ADS to one ordinary share to a new ADS Ratio of one ADS to ten ordinary shares. The ratio change became effective on March 10, 2023. The change in the ADS Ratio had the same effect as a one-for-ten reverse ADS split and is intended to enable the Company to regain compliance with the Nasdaq minimum bid price requirement. As all financial statement and disclosure information is presented in ordinary share amounts, not ADSs, there was no impact to the consolidated financial statements and footnote disclosures.

Issuance of shares through 2023 Private Placement

On March 6, 2023, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) pursuant to which the Company agreed to sell, in an unregistered offering, up to an aggregate of (i) 99,166,900 shares, consisting of a combination of Ordinary Shares, nominal value £0.10 per share (“Ordinary Shares”) and Non-Voting Ordinary Shares, nominal value £0.10 per share (“Non-Voting Ordinary Shares” and together with the Ordinary Shares, “Shares”) and (ii) warrants to purchase an aggregate of 109,083,590 Ordinary Shares or Non-Voting Ordinary Shares (the “Warrants”).

The 2023 Private Placement consists of two closings. The Company agreed to sell and issue in the initial closing of the 2023 Private Placement (i) 56,666,900 Shares and (ii) Warrants to purchase an aggregate of 62,333,590 Shares, at a purchase price of $6.00 per unit, where each unit consists of ten (10) Shares and an accompanying Warrant to purchase eleven (11) Shares. The initial closing of the 2023 Private Placement occurred on March 10, 2023. The Company received gross proceeds of approximately $34.0 million from the initial closing of the 2023 Private Placement, before deducting fees to the placement agent and other offering expenses payable by the Company.

In addition, the Company agreed to sell and issue in the second closing of the 2023 Private Placement (i) 42,500,000 Shares and (ii) Warrants to purchase an aggregate of 46,750,000 Shares, at a purchase price of $8.00 per unit, where each unit consists of ten (10) Shares and an accompanying Warrant to purchase eleven (11) Shares. The second closing is conditioned upon (x) the Company’s announcement of its intention to file a biologics license application (“BLA”) submission following receipt of the minutes from the U.S. Food and Drug Administration (“FDA”) in connection with the Company’s pre-BLA (Type B) meeting for OTL-200, provided such minutes do not expressly advise the Company not to proceed with a BLA submission, and (y) receipt of Shareholder Approval (as defined below) (collectively, the “Second Closing Trigger”).

In connection with the Private Placement, the Company has agreed to hold a meeting of its shareholders no later than 120 days following the initial closing of the Private Placement to seek approval to give the Company’s directors authority under s551 Companies Act 2006 to issue the securities to be issued and sold in the second closing of the Private Placement and the Shares issuable upon exercise of the Warrants to be issued and sold in the Private Placement, and to disapply pre-emption rights in respect of such authority under s570 of the Companies Act 2006 (collectively, “Shareholder Approval”).

The second closing is expected to occur on the fifth trading day after the Company notifies the purchasing parties that the Second Closing Trigger has occurred and is subject to additional, customary closing conditions. If the Second Closing Trigger occurs, the Company anticipates receiving gross proceeds of approximately $34.0 million from the second closing of

the 2023 Private Placement, before deducting fees to the placement agent and other offering expenses payable by the Company.

Each Warrant will have an exercise price equal to $1.10 per Share in the event the Vesting Event (as defined below) occurs on or prior to December 31, 2024, and $0.95 per Share in the event the Vesting Event occurs after December 31, 2024. The Warrants will be exercisable during the 30 days following the Company’s announcement of receipt of marketing approval of its BLA with respect to OTL-200 (the “Vesting Event”); provided that exercise of any Warrant is conditioned upon the receipt of Shareholder Approval. Commencement of the 30-day exercise period may be delayed as set forth in the Warrants in the event the Vesting Event occurs prior to Shareholder Approval. The Warrants will expire at the conclusion of the 30-day exercise period or, if the Vesting Event does not occur, March 10, 2026.