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Share-based payments - Fair value of options granted (Details)
12 Months Ended
Dec. 31, 2021
GBP (£)
Y
Dec. 31, 2021
GBP (£)
£ / shares
Dec. 31, 2021
GBP (£)
Dec. 31, 2020
GBP (£)
£ / shares
Share-based payments        
Weighted average fair value per option of options granted | £ £ 31.97 £ 31.97 £ 31.97 £ 6.70
Average share price at date of grant | £ / shares   £ 492.42   £ 40.36
Expected volatility (%)     50.00% 50.00%
Vesting period in years 4   4 1
Option life in years     4.25 4.00
Risk-free interest rate (%)     0.28% (0.13%)