The amount of outstanding funds that the entity is obligated to repay.

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The amount of assets that are: (a) cash; (b) an equity instrument of another entity; (c) a contractual right: (i) to receive cash or another financial asset from another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially favourable to the entity; or (d) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to receive a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose the entity’s own equity instruments do not include puttable financial instruments classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. [Refer: Financial instruments, class [member]; Financial liabilities]

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The amount of liabilities that are: (a) a contractual obligation: (i) to deliver cash or another financial asset to another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially unfavourable to the entity; or (b) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to deliver a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose, rights, options or warrants to acquire a fixed number of the entity’s own equity instruments for a fixed amount of any currency are equity instruments if the entity offers the rights, options or warrants pro rata to all of its existing owners of the same class of its own non-derivative equity instruments. Also, for those purposes the entity’s own equity instruments do not include puttable financial instruments that are classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. As an exception, an instrument that meets the definition of a financial liability is classified as an equity instrument if it has all the features and meets the conditions in paragraphs 16A-16B or paragraphs 16C-16D of IAS 32. [Refer: Financial instruments, class [member]; Financial assets; Derivatives [member]]

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The maturity of financial assets and liabilities maturity of contractual cash flows.

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Amount of cash paid in advance for clinical trials.

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Financial instruments (Details) $ in Millions	12 Months Ended
Financial instruments (Details) $ in Millions	Dec. 31, 2020 GBP (£)	Dec. 31, 2020 USD ($)	Nov. 06, 2020 USD ($)	Dec. 31, 2019 GBP (£)	Dec. 31, 2018 GBP (£)	Dec. 31, 2017 GBP (£)
Liquidity risk [Abstract]
Proceeds from agreement	£ 36,654,000			£ 0
Credit risk [Abstract]
Cash and cash equivalents	£ 129,716,000			73,966,000	£ 124,385,000	£ 82,883,000
Oxford Finance Agreement [Member]
Liquidity risk [Abstract]
Maturity date for monthly payments of principal and interest	Nov. 30, 2025
Oxford Finance Agreement, Tranche One [Member]
Liquidity risk [Abstract]
Proceeds from agreement \| $			$ 50
Liquidity Risk [Member]
Disclosure of financial assets [abstract]
Financial assets	£ 136,307,000			80,279,000
Disclosure of financial liabilities [abstract]
Financial liabilities	61,738,000			39,863,000
Liquidity Risk [Member] \| Trade Payables [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities	25,084,000			15,579,000
Liquidity Risk [Member] \| Interest Bearing Loans and Borrowings [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities	36,654,000			19,157,000
Liquidity Risk [Member] \| Derivative Liability [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities				5,127,000
Liquidity Risk [Member] \| Trade Receivables [Member]
Disclosure of financial assets [abstract]
Financial assets	1,797,000			1,471,000
Liquidity Risk [Member] \| Clinical Trial Deposits in Current Assets [Member]
Disclosure of financial assets [abstract]
Financial assets	1,221,000
Liquidity Risk [Member] \| Non-current Financial Assets [Member]
Disclosure of financial assets [abstract]
Financial assets	3,573,000
Liquidity Risk [Member] \| Interest Receivable [Member]
Disclosure of financial assets [abstract]
Financial assets				28,000
Liquidity Risk [Member] \| Prepayments and Accrued Income [Member]
Disclosure of financial assets [abstract]
Financial assets				2,282,000
Liquidity Risk [Member] \| Long Term Security Deposits [Member]
Disclosure of financial assets [abstract]
Financial assets				2,532,000
Liquidity Risk [Member] \| Cash and Cash Equivalents [Member]
Disclosure of financial assets [abstract]
Financial assets	129,716,000			73,966,000
Liquidity Risk [Member] \| Other Non-current Financial Assets [Member]
Liquidity risk [Abstract]
Paid in advance for clinical trials	3,426,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member]
Disclosure of financial assets [abstract]
Financial assets	136,307,000			80,279,000
Disclosure of financial liabilities [abstract]
Financial liabilities	76,505,000			35,005,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Trade Payables [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities	25,084,000			15,579,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Interest Bearing Loans and Borrowings [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities	51,421,000			19,426,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Derivative Liability [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities				0
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Trade Receivables [Member]
Disclosure of financial assets [abstract]
Financial assets	1,797,000			1,471,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Clinical Trial Deposits in Current Assets [Member]
Disclosure of financial assets [abstract]
Financial assets	1,221,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Non-current Financial Assets [Member]
Disclosure of financial assets [abstract]
Financial assets	3,573,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Interest Receivable [Member]
Disclosure of financial assets [abstract]
Financial assets				28,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Prepayments and Accrued Income [Member]
Disclosure of financial assets [abstract]
Financial assets				2,282,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Long Term Security Deposits [Member]
Disclosure of financial assets [abstract]
Financial assets				2,532,000
Liquidity Risk [Member] \| Financial Assets Contractual Cash Flows [Member] \| Cash and Cash Equivalents [Member]
Disclosure of financial assets [abstract]
Financial assets	129,716,000			73,966,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member]
Disclosure of financial assets [abstract]
Financial assets	132,734,000			75,889,000
Disclosure of financial liabilities [abstract]
Financial liabilities	28,438,000			39,863,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Trade Payables [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities	25,084,000			15,579,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Interest Bearing Loans and Borrowings [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities	3,354,000			19,157,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Derivative Liability [Member]
Disclosure of financial liabilities [abstract]
Financial liabilities				5,127,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Trade Receivables [Member]
Disclosure of financial assets [abstract]
Financial assets	1,797,000			1,471,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Clinical Trial Deposits in Current Assets [Member]
Disclosure of financial assets [abstract]
Financial assets	1,221,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Non-current Financial Assets [Member]
Disclosure of financial assets [abstract]
Financial assets	0
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Interest Receivable [Member]
Disclosure of financial assets [abstract]
Financial assets				28,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Prepayments and Accrued Income [Member]
Disclosure of financial assets [abstract]
Financial assets				424,000
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Long Term Security Deposits [Member]
Disclosure of financial assets [abstract]
Financial assets				0
Liquidity Risk [Member] \| Financial Assets Contractual Maturity One Year or Less [Member] \| Cash and Cash Equivalents [Member]
Disclosure of financial assets [abstract]
Financial assets	£ 129,716,000			73,966,000
Liquidity Risk [Member] \| Oxford Finance Agreement, Tranche One [Member]
Liquidity risk [Abstract]
Proceeds from agreement \| $		$ 50
Maturity date for monthly payments of principal and interest	Nov. 30, 2025
Liquidity Risk [Member] \| Bottom of Range [Member] \| Long Term Security Deposits [Member]
Liquidity risk [Abstract]
Financial assets estimated receivable period	P4Y
Liquidity Risk [Member] \| Bottom of Range [Member] \| Other Non-current Financial Assets [Member]
Liquidity risk [Abstract]
Financial assets estimated receivable period	P1Y
Liquidity Risk [Member] \| Top of Range [Member]
Liquidity risk [Abstract]
Financial assets and liabilities maturity of contractual cash flows	P1Y
Liquidity Risk [Member] \| Top of Range [Member] \| Other Non-current Financial Assets [Member]
Liquidity risk [Abstract]
Financial assets estimated receivable period	P5Y
Credit Risk [member]
Credit risk [Abstract]
Cash and cash equivalents	£ 129,716,000			£ 73,966,000