Income taxes - Components of net loss before tax provision from income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income taxes
United Kingdom	$ (116,275)	$ (69,546)	$ (52,521)
United States	2,034	1,064	787
Net loss before income tax provision	$ (114,241)	$ (68,482)	$ (51,734)