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Leases - Summary of Maturity Analysis of Lease Liabilities (Detail) - GBP (£)
£ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure Of Maturity Analysis Of Operating Lease Payments [Line Items]      
Total contractual undiscounted payments £ 677 £ 860  
Less: effect of discounting (32) (54)  
Discounted lease liabilities 645 806 £ 434
Not later than 1 year [member]      
Disclosure Of Maturity Analysis Of Operating Lease Payments [Line Items]      
Total contractual undiscounted payments 296 293  
Later than 1 year and not later than 3 years [member]      
Disclosure Of Maturity Analysis Of Operating Lease Payments [Line Items]      
Total contractual undiscounted payments 307 400  
Later than 3 years and not later than 5 years [member]      
Disclosure Of Maturity Analysis Of Operating Lease Payments [Line Items]      
Total contractual undiscounted payments £ 74 £ 167