v3.25.4
Deferred Income Tax - Additional Information (Detail) - GBP (£)
£ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deferred income tax assets £ 58 £ 52
Accruals and Other Provision 15 23
Other unrecognised tax losses 100 116
Other unrecognised tax losses Tax effect 34 39
Deferred tax liability (asset) 31 11
Gross Amount 896 965
Trading losses [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deferred income tax assets 0 9
Other [member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deductible temporary differences for which no deferred tax asset is recognised 198 194
Temporary Differences Interest Limitations [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deductible temporary differences for which no deferred tax asset is recognised 190 188
Temporary Differences Associated with Subsidiaries [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deductible temporary differences for which no deferred tax asset is recognised 274 290
Other Temporary Differences right of use assets deferred tax asset [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deferred tax liability (asset) 37 47
Other Temporary Differences right of use assets deferred tax liability [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deferred tax liability (asset) 33 37
Other Temporary Differences accelerated capital allowances [Member]    
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]    
Deferred tax liability (asset) £ 10 £ 11