Related party transactions - Summary of Related Party Transactions Outstanding (Details) - GBP (£) £ in Millions	Jun. 30, 2026	Dec. 31, 2025
Disclosure of transactions between related parties [abstract]
Amounts owed by related parties	£ 65	£ 105
Amounts owed to related parties	£ (171)	£ (126)

The amounts receivable resulting from related party transactions. [Refer: Total for all related parties [member]]

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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Name:	ifrs-full_AmountsReceivableRelatedPartyTransactions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant