v3.26.1
Income taxes - Reconciliation of benefit for income taxes (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Increase (decrease) as an amount      
Provision for (benefit from) income taxes at U.K. federal statutory rate $ (54,702)    
Changes in valuation allowance 19,869    
Net losses surrendered for research credit 21,626    
Impact of foreign exchange rates 13,893    
Total provision for (benefit from) income taxes $ 152 $ (4,765) $ 1,457
Tax Jurisdiction of Domicile [Extensible Enumeration] United Kingdom    
Increase (decrease) as a percent      
Provision for (benefit from) income taxes at U.K. federal statutory rate 25.00% 25.00% 23.50%
Changes in valuation allowance (9.10%) (11.20%) (14.80%)
Tax credits   3.70% 0.60%
Net losses surrendered for research credit (9.90%) (14.20%) (11.10%)
Impact of statutory rate change     2.70%
Impact of foreign exchange rates (6.30%) (1.00%) (0.10%)
Effective income tax rate (0.10%) 2.70% (0.80%)
United States      
Increase (decrease) as an amount      
Other $ (1,513)    
Increase (decrease) as a percent      
Other 0.70%    
United Kingdom      
Increase (decrease) as an amount      
Other $ 979    
Increase (decrease) as a percent      
Other (0.50%) 0.40% (1.60%)