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Income taxes, Reconciliation of Effective Income Tax Rate (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Effective Income Tax Rate [Abstract]      
U.K. statutory income tax rate 23.50% 19.00% 19.00%
Non-deductible expenses (1.10%) (20.70%) (9.80%)
Above the line credit not taxable (2.90%) 7.30% 1.40%
Additional deduction for R&D expenditure 0.00% 50.60% 9.40%
Surrender of tax losses for R&D tax credit refund 0.00% (9.60%) (9.40%)
R&D expenditure credits 5.30% (28.00%) 0.80%
Share based payments (3.00%) 0.00% 0.00%
State taxes 0.10% 1.30% 0.00%
Foreign rate differential 1.30% (0.50%) (0.10%)
Prior period adjustments 0.50% 0.40% (0.30%)
Leases 0.00% (0.40%) (0.40%)
Change in valuation allowances (14.50%) (47.90%) (10.70%)
Effective income tax rate 9.20% (28.50%) (0.10%)
R&D credits $ 5,745 $ 6,166  
Federal tax credits $ 5,300    
Tax credit carryforwards period 20 years    
United Kingdom [Member]      
Effective Income Tax Rate [Abstract]      
Profitability threshold for lower tax rates $ 2,500    
Operating loss carryforwards $ 286,000