Income taxes - Reconciliation of Effective Tax Rate (Details) - Her Majesty's Revenue and Customs (HMRC) |
12 Months Ended | 36 Months Ended | ||||
|---|---|---|---|---|---|---|
Apr. 01, 2020 |
Mar. 31, 2020 |
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2020 |
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| Income taxes | ||||||
| UK tax rate | 19.00% | 17.00% | 19.00% | 19.00% | 19.00% | 21.00% |
| Reimbursable tax credits within Research and development expense | 2.80% | 2.80% | 3.50% | |||
| R&D expenditures surrendered for R&D tax credit refund | (8.40%) | (7.70%) | (10.00%) | |||
| Expenses not deductible | (1.40%) | (0.20%) | ||||
| Permanent differences for unrealized foreign exchange on intercompany loans of a long-term investment nature | (1.50%) | |||||
| Change in valuation allowances | (17.80%) | (12.40%) | (17.50%) | |||
| Change in tax rates | 4.10% | |||||
| Difference in tax rates | (1.20%) | (1.30%) | ||||
| R&D tax credits generated | 1.80% | 1.50% | 5.10% | |||
| Other | (0.10%) | (0.70%) | 1.00% | |||
| Effective income tax rate | 0.00% | (0.20%) | (0.50%) | |||
| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to unrealized foreign exchange in subsidiary. No definition available.
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| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pre-tax income (loss) from continuing operations attributable to permanent difference relating to reimbursable tax credits. No definition available.
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| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pre-tax income (loss) from continuing operations attributable to the surrender of R&D expenditures for R&D tax credits. No definition available.
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| X | ||||||||||
- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- References No definition available.
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| X | ||||||||||
- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the income tax rates. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to statutory income tax expense (benefit) outside of the country of domicile. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to nondeductible expenses. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to research and development expense. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other adjustments. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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| X | ||||||||||
- Details
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