Tax - Narrative (Details) - GBP (£) £ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2022
Income taxes paid (refund) [abstract]
Deferred tax liability	£ 7,519	£ 7,181	£ 6,765

The amount of deferred tax liabilities or assets. [Refer: Deferred tax liabilities; Deferred tax assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2023-01-01
-Paragraph 81
-Subparagraph g
-Clause i
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=12&code=ifrs-tx-2023-en-r&anchor=para_81_g_i&doctype=Standard
-URIDate 2023-03-23

Name:	ifrs-full_DeferredTaxLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant