EARNINGS PER SHARE (Details) - GBP (£) £ in Millions, shares in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of earnings per share [text block] [Abstract]
Number of shares reserved for issue under options and contracts for sale of shares	38	57	140
Antidilutive Securities Excluded From Computation Of Earnings Per Share Number Of Shares	£ 0.0	£ 0.0	£ 0.3

The number of shares reserved for issue under options and contracts for the sale of shares.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 79
-Subparagraph a
-Clause vii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_79_a_vii&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_SharesReservedForIssueUnderOptionsAndContractsForSaleOfShares
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant