Income taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income taxes [Abstract]

Net Loss Before Income Taxes

Net loss before income taxes is as follows (in thousands):

	2023			2022			2021
United States	$	11,612		$	7,509		$	2,566
United Kingdom		(76,866	)		(47,566	)		(182,816	)
Other worldwide		4,364			(826	)		371
Net loss before income taxes	$	(60,890	)	$	(40,883	)	$	(179,879	)

Components of Income Tax Credit

The components of income tax credit are as follows (in thousands):

	2023			2022			2021
Current:
United Kingdom	$	—		$	(12,420	)	$	(54	)
United States - Federal and State		215			(968	)		(146	)
Other worldwide		(455	)		—			(43	)
Total current tax	$	(240	)	$	(13,388	)		(243	)
Deferred:
United Kingdom	$	—		$	—		$	—
United States - Federal and State		5,873			1,694			93
Other worldwide		(30	)		34			—
Total deferred tax	$	5,843		$	1,728		$	93
Total income tax credit (expense)	$	5,603		$	(11,660	)	$	(150	)

Deferred Tax Assets and Liabilities

The tax effects of temporary differences and carryforwards that give rise to deferred tax assets and liabilities were as follows (in thousands):

	2023			2022
Deferred tax assets
Net losses	$	74,916		$	73,059
Fixed assets		4,286			5,241
R&D credits		5,745			6,166
Corporate interest restriction		—			731
Stock based compensation		9,795			6,329
Other deferred tax assets		511			875
Total deferred tax assets	$	95,253		$	92,401
Deferred tax liabilities
Other deferred tax liabilities		(1,154	)		(844	)
Total deferred tax liabilities	$	(1,154	)	$	(844	)
Valuation allowance		(83,126	)		(86,436	)
Net deferred tax assets	$	10,973		$	5,121

Deferred Tax Asset Valuation Allowance

The movements in the deferred tax asset valuation allowances are as follows (in thousands):

	2023			2022
Valuation allowance as of January 1,	$	(86,436	)	$	(87,867	)
Decrease (Increase) in valuation allowance through net loss		7,573			(7,680	)
Foreign currency translation adjustments		(4,263	)		9,111
Valuation allowance as of December 31,	$	(83,126	)	$	(86,436	)

Reconciliation of Effective Income Tax Rate

Reconciliation of the U.K. statutory income tax rate, the income tax rate of the country of domicile of the Company, to the Company’s effective income tax rate is as follows (in percentages):

	2023		2022		2021
U.K. statutory income tax rate		23.5%		19.0%		19.0%
Non-deductible expenses		(1.1)%		(20.7)%		(9.8)%
Above the line credit not taxable		(2.9)%		7.3%		1.4%
Additional deduction for R&D expenditure		—		50.6%		9.4%
Surrender of tax losses for R&D tax credit refund		—		(9.6)%		(9.4)%
R&D expenditure credits		5.3%		(28.0)%		0.8%
Share based payments		(3.0)%		—		—
State taxes		0.1%		1.3%		—
Foreign rate differential		1.3%		(0.5)%		(0.1)%
Prior period adjustments		0.5%		0.4%		(0.3)%
Leases		—		(0.4)%		(0.4)%
Change in valuation allowances		(14.5)%		(47.9)%		(10.7)%
Effective income tax rate		9.2%		(28.5)%		(0.1)%

Tax Years Subject to Examination

The following table summarizes tax years that remain subject to examination by tax jurisdiction as of December 31, 2023:

Jurisdiction	Open Tax Years Based on Originally Filed Returns
United Kingdom	2021-2022
United States	2020-2022