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Income taxes | 12 Months Ended
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Dec. 31, 2024
Income taxes |
Income taxes | 10. Income taxes The components of net loss before income tax provision are as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended
​ | ​ | December 31,
​ |  | 2024 |  | 2023 |  | 2022
United Kingdom | ​ | $ | (179,610) | ​ | $ | (182,980) | ​ | $ | (116,275)
United States | ​ |  | 5,814 | ​ |  | 3,773 | ​ |  | 2,034
Total | ​ | $ | (173,796) | ​ | $ | (179,207) | ​ | $ | (114,241)
​ The components of the (benefit from) provision for income taxes are as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | Year Ended
​ | ​ | ​ | December 31,
​ |  | ​ | 2024 |  | 2023 |  | 2022
Current income tax provision (benefit) |  | ​ | ​ |  |  | ​ |  |  | ​ |
Federal | ​ | ​ | $ | 283 | ​ | $ | (1,180) | ​ | $ | 2,048
State | ​ | ​ |  | 178 | ​ |  | (669) | ​ |  | 1,404
Total current income tax provision (benefit) | ​ | ​ |  | 461 | ​ |  | (1,849) | ​ |  | 3,452
Deferred income tax (benefit) provision | ​ | ​ |  |  | ​ |  |  | ​ |  |
Federal | ​ | ​ |  | (3,772) | ​ |  | 2,513 | ​ |  | (4,111)
State | ​ | ​ |  | (1,454) | ​ |  | 793 | ​ |  | (865)
Total deferred income tax (benefit) provision | ​ | ​ |  | (5,226) | ​ |  | 3,306 | ​ |  | (4,976)
Total (benefit from) provision for income taxes | ​ | ​ | $ | (4,765) | ​ | $ | 1,457 | ​ | $ | (1,524)
​ A reconciliation of the (benefit from) provision for income taxes computed at the statutory income tax rate to the (benefit from) provision for income taxes as reflected in the financial statement is as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended | ​
​ | ​ | December 31, | ​
​ |  | 2024 |  | 2023 |  | 2022 | ​
(Benefit from) provision for income taxes at statutory rate |  | 25.0 | % | 23.5 | % | 19.0 | %
Increases (decreases) resulting from: | ​ | ​ | ​ | ​ | ​ | ​ | ​
Tax credits |  | 3.7 | % | 0.6 | % | 0.4 | %
Change in valuation allowance |  | (11.2) | % | (14.8) | % | (16.8) | %
Net losses surrendered for research credit |  | (14.2) | % | (11.1) | % | (6.5) | %
Impact of statutory rate change | ​ | — | % | 2.7 | % | 11.3 | %
Impact of foreign exchange rates | ​ | (1.0) | % | (0.1) | % | (9.9) | %
Other |  | 0.4 | % | (1.6) | % | 3.8 | %
Effective income tax rate |  | 2.7 | % | (0.8) | % | 1.3 | %
​ Significant components of the Company’s deferred tax assets are as follows (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​
​ | ​ | December 31,
​ |  | 2024 |  | 2023
Deferred tax assets: | ​ | ​ | ​ | ​ | ​ | ​
Operating loss carryforwards | ​ | $ | 81,492 | ​ | $ | 66,555
Research credit carryforwards | ​ |  | 3,362 | ​ |  | —
Operating lease liability | ​ | ​ | 2,641 | ​ | ​ | 3,680
Share-based compensation | ​ | ​ | 21,035 | ​ | ​ | 15,577
Depreciation & amortization | ​ | ​ | 1,508 | ​ | ​ | —
Accrued expenses and other | ​ |  | 1,952 | ​ |  | 2,742
Total deferred tax assets | ​ |  | 111,990 | ​ |  | 88,554
Deferred tax liabilities: | ​ | ​ | ​ | ​ | ​ | ​
Operating lease right-of-use asset | ​ | ​ | (2,201) | ​ | ​ | (3,389)
Total deferred tax liabilities | ​ |  | (2,201) | ​ |  | (3,389)
Valuation allowance | ​ |  | (99,672) | ​ |  | (80,274)
Net deferred tax assets | ​ | $ | 10,117 | ​ | $ | 4,891
​ During the years ended December 31, 2024, 2023 and 2022, the Company recorded an income tax benefit of $4.8 million, an income tax provision of $1.5 million and an income tax benefit of $1.5 million, respectively. The Company is subject to U.K. corporate taxation. Due to the nature of its business, the Company has generated losses since inception and therefore not paid U.K. corporation tax. The (benefit from) provision for income taxes included in the consolidated statements of operations and comprehensive loss represents the tax impact from operating activities in the United States, which has generated taxable income based on intercompany service arrangements. Deferred tax assets benefitted in the United States do not have a valuation allowance against them because of profits that will be generated by an intercompany service agreement. ​ The Company’s income tax benefit recognized during the year ended December 31, 2024 is mainly the result of deferred tax assets in the United States that do not have a valuation allowance against them because of profits that will be generated by an intercompany service agreement, including incremental income tax benefits of approximately $3.5 million recognized during the year ended December 31, 2024 related to the completion of a U.S. research and development tax credit study. The Company’s income tax provision recognized during the year ended December 31, 2023 is primarily related to the completion of an assessment, inclusive of an external tax analysis, during the year ended December 31, 2023, whereby the Company concluded that it is not required to capitalize certain research and development expenses incurred by its U.S. subsidiary associated with contractual research services performed on behalf of its U.K. subsidiary pursuant to an intercompany service arrangement because its U.S. subsidiary does not retain any ownership or rights in the underlying intellectual property resulting from the research services. The change in estimate upon the completion of this analysis resulted in the recognition of an income tax provision of $2.4 million during the year ended December 31, 2023. The Company's income tax benefit recognized during the years ended December 31, 2022 is mainly the result of deferred tax assets benefitted in the U.S. that do not have a valuation allowance against them because of profits that will be generated by an intercompany service agreement. The Company regularly assesses its ability to realize its deferred tax assets. Assessing the realization of deferred tax assets requires significant judgment. In determining whether its deferred tax assets are more likely than not realizable, the Company evaluated all available positive and negative evidence, and weighed the evidence based on its objectivity. After consideration of the evidence, including the Company's history of cumulative net losses in the U.K., the Company has concluded that it is more likely than not that the Company will not realize the benefits of its U.K. deferred tax assets and accordingly the Company has provided a valuation allowance for the full amount of the net deferred tax assets in the U.K. The Company has considered its history of cumulative net profits in the United States and estimated future taxable income and has concluded that it is more likely than not that the Company will realize the benefits of its United States deferred tax assets and has not provided a valuation allowance against the net deferred tax assets in the United States. The valuation allowance increased in the year ended December 31, 2024 by $19.4 million due to the corresponding increase in U.K. deferred tax assets, primarily due to operating loss carryforwards generated during the year that were not surrendered for research credit utilization. The Company recorded a valuation allowance against all of its U.K. deferred tax assets as of December 31, 2024 and 2023. The Company intends to continue to maintain a full valuation allowance on its U.K. deferred tax assets until there is sufficient evidence to support the reversal of all or some portion of these allowances. The release of the valuation allowance would result in the recognition of certain deferred tax assets and an increase to the benefit for income taxes for the period the release is recorded. However, the exact timing and amount of the valuation allowance release are subject to change on the basis of the level of profitability that the Company is able to actually achieve. The (benefit from) provision for income taxes shown on the consolidated statements of operations differs from amounts that would result from applying the statutory tax rates to income before taxes primarily because of certain permanent expenses that were not deductible and U.K., U.S. federal and state research and development credits, as well as the application of valuation allowances against the U.K. deferred tax assets. As of December 31, 2024, the Company had $326.0 million of U.K. operating loss carryforwards that have an indefinite life. The Company recognizes, in its consolidated financial statements, the effect of a tax position when it is more likely than not, based on the technical merits, that the position will be sustained upon examination. The Company had no uncertain tax positions during the years ended December 31, 2024 and 2023. There are no amounts of interest or penalties recognized in the consolidated statement of operations or accrued on the consolidated balance sheet for any period presented. The Company does not expect any material changes in these uncertain tax benefits within the next 12 months. The Company files income tax returns in the United Kingdom, and in the United States for federal income taxes and in 11 jurisdictions for state income taxes. In the normal course of business, the Company is subject to examination by tax authorities in these jurisdictions. The 2023 and 2022 tax years remain open to examination by the HM Revenue & Customs. The statute of limitations for assessment with the Internal Revenue Service is generally three years from filing the tax return. As such, all years since 2021 in the U.S. remain open to examination. The Company is currently not under examination by jurisdictions for any tax years.

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