BASIS OF PREPARATION AND SIGNIFICANT ACCOUNTING POLICIES - Hyperinflationary reporting (Details) - GBP (£) £ in Millions	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025
BASIS OF PREPARATION AND SIGNIFICANT ACCOUNTING POLICIES
Retained earnings	£ 27,687		£ 27,847
Hyperinflationary reporting, effect on revenue in the period	7
Hyperinflationary reporting, effect on operating profit in the period	2
Net monetary gain arising from hyperinflationary economies	£ 3	£ 1

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Hyperinflationary reporting, effect on operating profit (loss) in the period

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Hyperinflationary reporting, effect on revenue in the period

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The gains (losses) representing the difference resulting from the restatement of non-monetary assets, owners' equity and items in the statement of comprehensive income and the adjustment of index linked assets and liabilities in hyperinflationary reporting.

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A component of equity representing the entity's cumulative undistributed earnings or deficit.

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