Financial instruments and risk management - Management of Financial Risks, Additional Information (Details) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Abstract]
Proportion of average cost of debt	4.90%	5.20%
Adjustments for gains (losses) on change in fair value of derivatives		£ 151
Proportion of average cost of debt, excluding adjusting items	4.80%

Adjustments for gains (losses) on changes in the fair value of derivatives to reconcile profit (loss) to net cash flow from (used in) operating activities. [Refer: At fair value [member]; Derivatives [member]; Profit (loss)]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2024-01-01
-Paragraph 20
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=7&code=ifrs-tx-2024-en-r&anchor=para_20&doctype=Standard
-URIDate 2024-03-27

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