Taxation - Net deferred tax assets and liabilities (Details) - GBP (£) £ in Millions	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2019
Income Taxes [Abstract]
Deferred tax assets	£ 100	£ 119
Deferred tax liabilities	(1,945)	(1,972)
Net deferred tax liabilities	£ (1,845)	£ (1,853)	£ (1,894)

The amounts of income taxes recoverable in future periods in respect of: (a) deductible temporary differences; (b) the carryforward of unused tax losses; and (c) the carryforward of unused tax credits. [Refer: Temporary differences [member]; Unused tax credits [member]; Unused tax losses [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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