Investments in joint ventures and associates - Disclosure of aggregate information of associates and joint venture (Details) - GBP (£) £ in Millions	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
Disclosure of joint ventures [line items]
Share of post-tax results of joint ventures and associates	£ 76	£ 73	£ 37
Impairment	0	(303)
Aggregated individually immaterial associates and joint ventures
Disclosure of joint ventures [line items]
Share of post-tax results of joint ventures and associates	6	24
Impairment	0	(303)
Share of total comprehensive income	6	(279)
Aggregate carrying value of the Group’s interests	£ 226	£ 216

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

No definition available.

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- References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 133
-Subparagraph a
-Clause iv
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-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 99
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_99&doctype=Standard
-URIDate 2025-03-27

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- Definition

The amount of investments in subsidiaries, joint ventures and associates in an entity's separate financial statements. [Refer: Total for all associates [member]; Total for all joint ventures [member]; Total for all subsidiaries [member]; Investments in subsidiaries reported in separate financial statements]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 27
-IssueDate 2025-01-01
-Paragraph 10
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=27&code=ifrs-tx-2025-en-r&anchor=para_10&doctype=Standard
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- References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 8
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-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Note Expiry date 2027-01-01
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- Definition

The entity's share of the total comprehensive income of associates and joint ventures accounted for using the equity method. [Refer: Total for all associates [member]; Total for all joint ventures [member]; Investments accounted for using equity method]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-IssueDate 2025-01-01
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