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Income tax (Details) - GBP (£)
1 Months Ended 12 Months Ended
Apr. 01, 2020
Mar. 11, 2020
Apr. 01, 2017
Sep. 30, 2016
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Tax rate [Abstract]              
Deferred tax asset, unrecognised         £ 30,827,000 £ 20,820,000  
Tax credit increase         33,852,000 23,007,000  
Unused tax credits [Member]              
Tax rate [Abstract]              
Deferred tax asset, recognised         £ 2,230,000 £ 1,507,000  
UK [Member]              
Tax rate [Abstract]              
Tax rate 17.00% 19.00% 19.00% 20.00% 19.00% 19.00% 19.00%