Ordinary shares (Details)	3 Months Ended
	Mar. 31, 2022 item £ / shares $ / shares shares	Mar. 31, 2021 $ / shares	Dec. 31, 2021 £ / shares shares
Ordinary shares.
Vote per ordinary share | item	1
Dividends declared | $ / shares	$ 0	$ 0
Ordinary shares, shares authorized | shares	57,070,181		55,295,420
Ordinary shares, nominal value | £ / shares	$ 0.01		£ 0.01