BASIS OF PREPARATION (Details) £ in Millions	12 Months Ended
Dec. 31, 2017 GBP (£)
Disclosure of basis of preparation of financial statements [text block] [Abstract]
Right-of-use assets, increase (decrease) in revaluation surplus	£ 40

The increase (decrease) in the revaluation surplus that relates to right-of-use assets. [Refer: Revaluation surplus; Right-of-use assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2019-01-01
-Name IFRS
-Number 16
-IssueDate 2016-01-13
-Paragraph 57
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=16&date=2016-03-30&anchor=para_57&doctype=Standard
-URIDate 2016-03-31

Name:	ifrs-full_RightofuseAssetsIncreaseDecreaseInRevaluationSurplus
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration