Deferred tax - Additional Information (Details) - GBP (£)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Temporary Difference Unused Tax Losses And Unused Tax Credits [Line Items]
U.K. corporation tax rate	19.00%	19.00%	19.00%
In Respect of Capital Losses
Disclosure Of Temporary Difference Unused Tax Losses And Unused Tax Credits [Line Items]
Deferred tax expense (income) recognized in profit or loss	£ 0	£ 0

The amount of tax expense or income relating to changes in deferred tax liabilities and deferred tax assets, recognised in profit or loss. [Refer: Deferred tax assets; Deferred tax expense (income); Deferred tax liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2021-01-01
-Paragraph 81
-Subparagraph g
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2021-en-r&anchor=para_81_g_ii&doctype=Standard
-URIDate 2021-03-24

Name:	ifrs-full_DeferredTaxExpenseIncomeRecognisedInProfitOrLoss
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration