CONSOLIDATED CASH FLOW STATEMENT (Details) - Narrative - GBP (£) £ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of cash flow statement [Abstract]
Cash and cash equivalents held by entity unavailable for use by group	£ 84	£ 49	£ 40

The amount of significant cash and cash equivalent balances held by the entity that are not available for use by the group. [Refer: Cash and cash equivalents]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 7
-IssueDate 2020-01-01
-Paragraph 48
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2020-en-r&anchor=para_48&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_CashAndCashEquivalentsHeldByEntityUnavailableForUseByGroup
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant