Related-party transactions - Disclosure of transactions between related parties (Details) - GBP (£) £ in Thousands	3 Months Ended
Apr. 30, 2018	Apr. 30, 2017
Directors of the Company
Disclosure of transactions between related parties [line items]
Aggregate emoluments	£ 152	£ 176
Pension contributions	5	5
Employee benefits expense	157	181
Directors of the Company and key management
Disclosure of transactions between related parties [line items]
Aggregate emoluments	311	276
Pension contributions	13	10
Employee benefits expense	£ 324	£ 286

The expense of all forms of consideration given by an entity in exchange for a service rendered by employees or for the termination of employment.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 102
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_102&doctype=Standard
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 99
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_99&doctype=Standard
-URIDate 2017-03-09

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 104
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_104&doctype=Standard
-URIDate 2017-03-09

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