The number of dilutive potential ordinary shares that relate to the assumed conversion of the entity's convertible instruments.

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The increase (decrease) in the number of shares outstanding. [Refer: Number of shares outstanding]

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The number of shares issued by the entity.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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The number of shares issued by the entity, for which full payment has been received.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The nominal value per share.

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The cash inflow from issuing shares.

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The amount of cost related to the issuance of shares.

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- Definition

The number of equity shares converted during the period.

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No definition available.

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Price of a single share of a number of saleable stocks of a company.

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The balance of deferred income is associated with this target amount.

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No definition available.

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- Definition

The nominal value of common shares.

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No definition available.

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Events after the reporting period (Details)				12 Months Ended
Events after the reporting period (Details)	Feb. 09, 2021 USD ($)	Feb. 01, 2021 £ / shares shares	Jan. 22, 2021 shares	Dec. 31, 2020 shares	Dec. 31, 2019 shares	Dec. 31, 2018 shares	Mar. 31, 2021 GBP (£)	Feb. 09, 2021 GBP (£) shares	Feb. 09, 2021 $ / shares
Events after reporting period [Abstract]
Ordinary shares cancelled creating distributable reserve (in shares)				83,115	59,163	101
Ordinary Shares [Member]
Events after reporting period [Abstract]
Ordinary shares cancelled creating distributable reserve (in shares)				163,870	45,581	10,950
Growth Shares [Member]
Events after reporting period [Abstract]
Ordinary shares cancelled creating distributable reserve (in shares)				34,260	0	0
Forecast [Member]
Events after reporting period [Abstract]
Ordinary shares cancelled creating distributable reserve (in shares)			6,414,412
Forecast [Member] \| GlaxoSmithKline [Member]
Events after reporting period [Abstract]
Target amount for release of deferred income \| £							£ 3,208,000
Forecast [Member] \| Growth Shares [Member]
Events after reporting period [Abstract]
Shares converted (in shares)		1,926,000
Forecast [Member] \| Non-voting Ordinary Shares [Member]
Events after reporting period [Abstract]
Share conversion (in shares)		1
Shares converted (in shares)		831,627
Forecast [Member] \| Deferred Shares [Member]
Events after reporting period [Abstract]
Share conversion (in shares)		3
Shares converted (in shares)		4,349,000
Forecast [Member] \| Immunocore Holdings Limited [Member]
Events after reporting period [Abstract]
Share conversion (in shares)			0.01					0.01
Share price (in pounds per share) \| £ / shares		£ 0.002
Funding costs including underwriter fee \| $	$ 25,196,000
Forecast [Member] \| Immunocore Holdings Limited [Member] \| Ordinary Shares [Member]
Events after reporting period [Abstract]
Share conversion (in shares)		1
Shares issued in initial public offering (in shares)		20						11,426,280
Par value per share (in pounds per share) \| £ / shares		£ 0.0001
Nominal value of ordinary shares \| £								£ 23,000
Forecast [Member] \| Immunocore Holdings Limited [Member] \| IPO [Member]
Events after reporting period [Abstract]
Proceeds from shares issued \| $	297,083,000
Forecast [Member] \| Immunocore Holdings Limited [Member] \| ADS [Member]
Events after reporting period [Abstract]
Share price (in pounds per share) \| $ / shares									$ 26.00
Proceeds from shares issued \| $	$ 15,000,000
Additional ADS issued (in shares)								576,923
Forecast [Member] \| Immunocore Holdings Limited [Member] \| Non-voting Ordinary Shares [Member]
Events after reporting period [Abstract]
Shares issued in initial public offering (in shares)		20
Par value per share (in pounds per share) \| £ / shares		£ 0.0001