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Share-based Payments - Disclosure of stock option activity (Details)
 12 Months Ended
Dec. 31, 2022
shares
£ / shares
Dec. 31, 2021
shares
£ / shares
Dec. 31, 2020
shares
£ / shares
Dec. 31, 2019
shares
£ / shares
Disclosure of share capital, reserves and other equity interest [Abstract]        
Outstanding at beginning of period (in shares) | shares 13,414,118 10,916,086 8,472,827  
Granted (in shares) | shares 8,881,000 5,424,000 4,076,982  
Exercised (in shares) | shares (577,022) (2,238,187) (514,410)  
Forfeited and expired (in shares) | shares (3,924,215) (687,781) (1,119,313)  
Options exercisable (in shares) | shares 6,185,216 4,773,873 5,447,405  
Outstanding at end of period (in shares) | shares 17,793,881 13,414,118 10,916,086 8,472,827
Weighted-average exercise price, beginning of year (in GBP per share) £ 2.58 £ 1.81 £ 1.16  
Weighted average exercise price, options granted (in GBP per share) 2.04 3.34 3.14  
Weighted average exercise price, options exercised (in GBP per share) 0.50 0.70 1.52  
Weighted average exercise price, options forfeited and expired (in GBP per share) 2.89 2.53 1.88  
Weighted average exercise price of, options exercisable (in GBP per share) 2.03 1.42 0.98  
Weighted-average exercise price, end of year (in GBP per share) £ 2.31 £ 2.58 £ 1.81 £ 1.16
Weighted average remaining contractual life of outstanding share options (in years) 8 years 10 days 8 years 3 months 14 days 8 years 4 months 17 days 8 years 6 months 18 days
Weighted average remaining contractual life of options excisable (in years) 6 years 2 months 15 days 6 years 6 months 7 years 5 months 15 days  
Weighted average stock price of share options exercised in share-based payment arrangement (in GBP per share) £ 2.43 £ 3.63 £ 2.88