Tax - Schedule of deferred tax assets not recognised (Details) - GBP (£) £ in Millions	Mar. 31, 2026	Mar. 31, 2025
Capital losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax assets not recognised	£ 2,482	£ 2,484
Trading losses
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Deferred tax assets not recognised	£ 9	£ 9

The amount of unused tax losses for which no deferred tax asset is recognised in the statement of financial position. [Refer: Unused tax losses [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2025-01-01
-Paragraph 81
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2025-en-r&anchor=para_81_e&doctype=Standard
-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 194
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_194_e&doctype=Standard
-URIDate 2025-03-27

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 194
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_194_e&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_UnusedTaxLossesForWhichNoDeferredTaxAssetRecognised
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant