v3.26.1
FINANCIAL INSTRUMENTS AND RELATED DISCLOSURES - Financial instruments held at fair value by fair value hierarchy (Details) - GBP (£)
£ in Millions
Jun. 30, 2026
Dec. 31, 2025
Financial liabilities at fair value through profit or loss    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities £ (141) £ (65)
Financial liabilities at fair value through profit or loss | Level 2    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (141) (65)
Financial liabilities at fair value through profit or loss | Held for trading derivatives that are not in a designated and effective hedging relationship    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (5) (3)
Financial liabilities at fair value through profit or loss | Held for trading derivatives that are not in a designated and effective hedging relationship | Level 2    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (5) (3)
Financial liabilities at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Fair value hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (42) (24)
Financial liabilities at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Cash flow hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (22) (10)
Financial liabilities at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Net investment hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (72) (28)
Financial liabilities at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Level 2 | Fair value hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (42) (24)
Financial liabilities at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Level 2 | Cash flow hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (22) (10)
Financial liabilities at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Level 2 | Net investment hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial liabilities (72) (28)
Financial assets at fair value    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 296 762
Financial assets at fair value | Level 1    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 173 608
Financial assets at fair value | Level 2    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 54 87
Financial assets at fair value | Level 3    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 69 67
Financial assets at fair value through other comprehensive income | Equity investments    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 69 67
Financial assets at fair value through other comprehensive income | Equity investments | Level 3    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 69 67
Financial assets at fair value through profit or loss | Held for trading derivatives that are not in a designated and effective hedging relationship    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 23 26
Financial assets at fair value through profit or loss | Held for trading derivatives that are not in a designated and effective hedging relationship | Level 2    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 23 26
Financial assets at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Fair value hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 2 3
Financial assets at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Cash flow hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 13 11
Financial assets at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Net investment hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 16 47
Financial assets at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Level 2 | Fair value hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 2 3
Financial assets at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Level 2 | Cash flow hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 13 11
Financial assets at fair value through profit or loss | Derivatives designated and effective as hedging instruments | Level 2 | Net investment hedge    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 16 47
Financial assets at fair value through profit or loss | Cash and cash equivalents (money market funds)    
Financial instruments held at fair value by fair value hierarchy    
Financial assets 173 608
Financial assets at fair value through profit or loss | Cash and cash equivalents (money market funds) | Level 1    
Financial instruments held at fair value by fair value hierarchy    
Financial assets £ 173 £ 608