v3.25.4
Treasury shares - Additional Information (Detail) - GBP (£)
£ / shares in Units, £ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Treasury shares transaction [line items]      
Percentage of called up share capital 0.10% 0.10%  
Treasury shares held, par value £ 0.25 £ 0.25  
Treasury shares, nominal value £ 0.2 £ 0.2  
Treasury shares, market value 8.0 9.0  
Treasury shares £ 9.0 7.0  
Treasury shares [member]      
Treasury shares transaction [line items]      
Treasury shares held, par value £ 0.25    
Treasury shares £ 9.0 £ 7.0 £ 19.0