Tax (Details) - GBP (£) £ in Millions	6 Months Ended	12 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Mar. 31, 2026
Income taxes paid (refund) [abstract]
Tax on exceptional items and remeasurements	£ 386	£ 208
Average effective tax rate	(22.30%)	(25.20%)	22.50%

- References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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+ Details