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FINANCIAL INSTRUMENTS AND RELATED DISCLOSURES - Carrying value and fair value of financial instruments (Details) - Carrying value - Bonds - GBP (£)
£ in Millions
Jun. 30, 2023
Dec. 31, 2022
Carrying value and fair value of financial instruments    
Carrying value, Financial liabilities £ 9,191 £ 9,861
Fair value, Financial Liabilities £ 8,483 £ 9,016