| 
             Three Months Ended March 31, 
           | 
          ||||||||||||
| 
              2022 
           | 
          
             2021 
           | 
          |||||||||||
| 
             $ 
           | 
          
             ’000 
           | 
          
             £ 
           | 
          
             ’000 
           | 
          
             £ 
           | 
          
             ’000 
           | 
          |||||||
| 
             Product revenue, net 
           | 
          
             10,103 
           | 
          
             7,682 
           | 
          
             — 
           | 
          |||||||||
| 
             Pre-product revenue, net 
           | 
          
             3,721 
           | 
          
             2,829 
           | 
          
             — 
           | 
          |||||||||
| 
             Collaboration revenue 
           | 
          
             15,734 
           | 
          
             11,963 
           | 
          
             8,270 
           | 
          |||||||||
| 
             Total revenue 
           | 
          
             29,558 
           | 
          
             22,474 
           | 
          
             8,270 
           | 
          |||||||||
| 
             Cost of product revenue 
           | 
          
             (326 
           | 
          
             ) 
           | 
          
             (248 
           | 
          
             ) 
           | 
          
             — 
           | 
          |||||||
| 
             Research and development expenses 
           | 
          
             (24,438 
           | 
          
             ) 
           | 
          
             (18,581 
           | 
          
             ) 
           | 
          
             (19,885 
           | 
          
             ) 
           | 
        ||||||
| 
             Selling and administrative expenses 
           | 
          
             (26,443 
           | 
          
             ) 
           | 
          
             (20,106 
           | 
          
             ) 
           | 
          
             (20,184 
           | 
          
             ) 
           | 
        ||||||
| 
             Net other operating income / (expense) 
           | 
          
             1 
           | 
          
             1 
           | 
          
             (82 
           | 
          
             ) 
           | 
        ||||||||
| 
             Operating loss 
           | 
          
             (21,648 
           | 
          
             ) 
           | 
          
             (16,460 
           | 
          
             ) 
           | 
          
             (31,881 
           | 
          
             ) 
           | 
        ||||||
| 
             Finance income 
           | 
          
             13 
           | 
          
             10 
           | 
          
             22 
           | 
          |||||||||
| 
             Finance costs 
           | 
          
             (1,753 
           | 
          
             ) 
           | 
          
             (1,333 
           | 
          
             ) 
           | 
          
             (1,860 
           | 
          
             ) 
           | 
        ||||||
| 
             Non-operating expense 
           | 
          
             (1,740 
           | 
          
             ) 
           | 
          
             (1,323 
           | 
          
             ) 
           | 
          
             (1,838 
           | 
          
             ) 
           | 
        ||||||
| 
             Loss before taxes 
           | 
          
             (23,388 
           | 
          
             ) 
           | 
          
             (17,783 
           | 
          
             ) 
           | 
          
             (33,719 
           | 
          
             ) 
           | 
        ||||||
| 
             Income tax credit 
           | 
          
             2,177 
           | 
          
             1,655 
           | 
          
             4,681 
           | 
          |||||||||
| 
             Loss for the period 
           | 
          
             (21,211 
           | 
          
             ) 
           | 
          
             (16,128 
           | 
          
             ) 
           | 
          
             (29,038 
           | 
          
             ) 
           | 
        ||||||
| 
             Three Months Ended March 31, 
           | 
          ||||||||||||
| 
              2022 
           | 
          
             2022 
           | 
          
             2021 
           | 
          ||||||||||
| 
             $ 
           | 
          
             ’000 
           | 
          
             £ 
           | 
          
             ’000 
           | 
          
             £ 
           | 
          
             ’000 
           | 
          |||||||
| 
             | 
          ||||||||||||
| 
             Cash and cash equivalents at beginning of year 
           | 
          
             312,868 
           | 
          
             237,886 
           | 
          
             129,716 
           | 
          |||||||||
| 
             Net cash flows used in operating activities 
           | 
          
             (40,552 
           | 
          
             ) 
           | 
          
             (30,833 
           | 
          
             ) 
           | 
          
             (25,979 
           | 
          
             ) 
           | 
        ||||||
| 
             Net cash flows (used in) / from investing activities 
           | 
          
             (175 
           | 
          
             ) 
           | 
          
             (133 
           | 
          
             ) 
           | 
          
             25 
           | 
          |||||||
| 
             Net cash flows (used in) / from financing activities 
           | 
          
             (1,752 
           | 
          
             ) 
           | 
          
             (1,332 
           | 
          
             ) 
           | 
          
             209,373 
           | 
          |||||||
| 
             Net foreign exchange difference on cash held 
           | 
          
             349 
           | 
          
             265 
           | 
          
             (52 
           | 
          
             ) 
           | 
        ||||||||
| 
             Cash and cash equivalents at end of period 
           | 
          
             270,738 
           | 
          
             205,853 
           | 
          
             313,083 
           | 
          |||||||||
| 
             March 31, 
            2022 
            £’000 
           | 
          
             December 31, 
            2021 
            £’000 
           | 
          |||||||
| 
             Non-current assets 
           | 
          ||||||||
| 
             Property, plant and equipment 
           | 
          
             7,849 
           | 
          
             8,944 
           | 
          ||||||
| 
             Right of use assets 
           | 
          
             22,199 
           | 
          
             22,593 
           | 
          ||||||
| 
             Other non-current assets 
           | 
          
             5,955 
           | 
          
             4,935 
           | 
          ||||||
| 
             Deferred tax asset 
           | 
          
             2,650 
           | 
          
             2,575 
           | 
          ||||||
| 
             Total non-current assets 
           | 
          
             38,653 
           | 
          
             39,047 
           | 
          ||||||
| 
             Current assets 
           | 
          ||||||||
| 
             Inventory 
           | 
          
             496 
           | 
          
             — 
           | 
          ||||||
| 
             Trade and other receivables 
           | 
          
             25,746 
           | 
          
             15,208 
           | 
          ||||||
| 
             Tax receivable 
           | 
          
             11,289 
           | 
          
             9,632 
           | 
          ||||||
| 
             Cash and cash equivalents 
           | 
          
             205,853 
           | 
          
             237,886 
           | 
          ||||||
| 
             Total current assets 
           | 
          
             243,384 
           | 
          
             262,726 
           | 
          ||||||
| 
             Total assets 
           | 
          
             282,037 
           | 
          
             301,773 
           | 
          ||||||
| 
             Equity 
           | 
          ||||||||
| 
             Share capital 
           | 
          
             88 
           | 
          
             88 
           | 
          ||||||
| 
             Share premium 
           | 
          
             212,499 
           | 
          
             212,238 
           | 
          ||||||
| 
             Foreign currency translation reserve 
           | 
          
             294 
           | 
          
             89 
           | 
          ||||||
| 
             Other reserves 
           | 
          
             386,167 
           | 
          
             386,167 
           | 
          ||||||
| 
             Share-based payment reserve 
           | 
          
             61,770 
           | 
          
             54,357 
           | 
          ||||||
| 
             Accumulated deficit 
           | 
          
             (497,520 
           | 
          
             ) 
           | 
          
             (481,392 
           | 
          
             ) 
           | 
        ||||
| 
             Total equity 
           | 
          
             163,298 
           | 
          
             171,547 
           | 
          ||||||
| 
             Non-current liabilities 
           | 
          ||||||||
| 
             Interest-bearing loans and borrowings 
           | 
          
             38,370 
           | 
          
             37,226 
           | 
          ||||||
| 
             Deferred revenue 
           | 
          
             2,136 
           | 
          
             6,408 
           | 
          ||||||
| 
             Lease liabilities 
           | 
          
             25,043 
           | 
          
             25,355 
           | 
          ||||||
| 
             Provisions 
           | 
          
             70 
           | 
          
             57 
           | 
          ||||||
| 
             Total non-current liabilities 
           | 
          
             65,619 
           | 
          
             69,046 
           | 
          ||||||
| 
             Current liabilities 
           | 
          ||||||||
| 
             Trade and other payables 
           | 
          
             34,695 
           | 
          
             35,436 
           | 
          ||||||
| 
             Deferred revenue 
           | 
          
             17,089 
           | 
          
             24,450 
           | 
          ||||||
| 
             Lease liabilities 
           | 
          
             1,294 
           | 
          
             1,255 
           | 
          ||||||
| 
             Provisions 
           | 
          
             42 
           | 
          
             39 
           | 
          ||||||
| 
             Total current liabilities 
           | 
          
             53,120 
           | 
          
             61,180 
           | 
          ||||||
| 
             Total liabilities 
           | 
          
             118,739 
           | 
          
             130,226 
           | 
          ||||||
| 
             Total equity and liabilities 
           | 
          
             282,037 
           | 
          
             301,773 
           | 
          ||||||