Operating costs - Other external charges (Details) - GBP (£) £ in Millions	12 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Analysis of income and expense [abstract]
Research and development expenditure	£ 34	£ 35	£ 36
Maintenance and repairs expense	£ 105	£ 103	£ 117

The amount of expenses incurred for the day-to-day servicing of assets, which may include the cost of labour, consumables or small parts.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 85
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_85&doctype=Standard
-URIDate 2019-03-27

Name:	ifrs-full_RepairsAndMaintenanceExpense
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration