v3.26.1
ASSETS CHARGED AS SECURITY FOR LIABILITIES AND COLLATERAL ACCEPTED AS SECURITY FOR ASSETS (Details) - GBP (£)
£ in Millions
 6 Months Ended
Jun. 30, 2026
Dec. 31, 2025
Disclosure Of Assets Pledged As Security [Line Items]    
Gross assets charged as security for liabilities £ 47,815 £ 37,123
TSB    
Disclosure Of Assets Pledged As Security [Line Items]    
Increase in assets recognised in entity's financial statements in relation to structured entities 7,727  
Increase in note issuances available for creating collateral 1,492  
Internally retained | Securitisations and covered bonds    
Disclosure Of Assets Pledged As Security [Line Items]    
Notes issued under securitisation and covered bond programmes retained internally 6,563 2,975
Internally retained | Securitisations and covered bonds | Santander UK Plc    
Disclosure Of Assets Pledged As Security [Line Items]    
Internally retained securitisation and covered bond issuances available for creating collateral 3,708 657
Third party bilateral secured funding transactions | Securitisations and covered bonds    
Disclosure Of Assets Pledged As Security [Line Items]    
Financial assets pledged as collateral for liabilities or contingent liabilities £ 2,293 £ 1,500