v3.26.1
Income Tax - Schedule of Major Components of Income Tax Credit (Detail) - GBP (£)
£ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Current tax:        
Total current tax £ 330 £ 325 £ 737 £ 672
Deferred tax:        
Income tax credit 333 328 743 681
U.K. [member]        
Current tax:        
In respect of current period 330 301 737 648
In respect of prior period   24   24
U.S. [member]        
Deferred tax:        
In respect of current period £ 3 £ 3 £ 6 £ 9