Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Options (Details)

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Summary of Significant Accounting Policies - Options (Details) - £ / shares
2 Months Ended
Feb. 29, 2020
Dec. 31, 2019
Dec. 31, 2018
Nominal value of ordinary shares £ 0.001 £ 0.001 £ 0.001
Exercise price determined by reference to the market value of an ADS at the date of grant      
Number of options granted (in shares) 10,229,280    
Exercise price equal to the nominal value of the ordinary shares      
Number of options granted (in shares) 6,060,696