Mereo BioPharma (MREO) 20-F 15 Jun 20 2019 FY Annual report (foreign) Financial data

Cover Page

Cover Page	12 Months Ended
	Dec. 31, 2019shares
Cover [Abstract]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	MREO
Entity Registrant Name	Mereo Biopharma Group plc
Entity Central Index Key	0001719714
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding	97,959,622
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Address, Country	GB
Document Annual Report	true
Document Transition Report	false
Document Shell Company Report	false
Title of 12(b) Security	Common Shares
Security Exchange Name	NASDAQ

Consolidated statement of compr

Consolidated statement of comprehensive loss - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of comprehensive income [abstract]
Research and development expenses	£ (23,608)	£ (22,703)	£ (34,607)
Administrative expenses	(15,909)	(11,775)	(10,697)
Operating loss	(39,517)	(34,478)	(45,304)
Net income recognized on acquisition of subsidiary	1,035
Finance income	377	307	827
Finance charge	(3,496)	(3,091)	(1,090)
Net foreign exchange (loss)/gain	483	(44)	(1,384)
Loss before tax	(41,118)	(37,306)	(46,951)
Taxation	6,274	5,277	8,152
Loss attributable to equity holders of the parent	(34,844)	(32,029)	(38,799)
Other comprehensive income – items that may be reclassified to profit or loss
Net fair value gain / (loss) on investments in debt instruments held at fair value
Exchange differences on translation of foreign operations	(499)
Other comprehensive income, net of tax	(499)
Total comprehensive loss attributable to equity holders of the parent	£ (35,343)	£ (32,029)	£ (38,799)
Basic and diluted loss per share	£ (0.39)	£ (0.45)	£ (0.56)

Consolidated balance sheet

Consolidated balance sheet - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Non-current assets
Property, plant and equipment	£ 11,558	£ 149
Intangible assets	44,456	32,632
Total non-current assets	56,014	32,781
Current assets
Prepayments	2,111	1,067
R&D tax credits	10,426	5,277
Other taxes recoverable	979
Other receivables	572	609
Short-term investments		2,500
Cash and short-term deposits	16,347	25,042
Total current assets	30,435	34,495
Total assets	86,449	67,276
Equity
Issued capital	294	214
Share premium	121,684	118,492
Other capital reserves	59,147	18,593
Employee Benefit Trust shares	(1,305)	(307)
Other reserves	7,000	7,000
Accumulated loss	(146,065)	(111,221)
Translation reserve	(499)
Total equity	40,256	32,771
Non-current liabilities
Provisions	1,449	2,641
Interest-bearing loans and borrowings	5,373	14,647
Warrant liability	131	1,006
Other liabilities	44	34
Lease liability	9,318
Total non-current liabilities	16,315	18,328
Current liabilities
Trade and other payables	6,352	4,570
Accruals	5,138	4,437
Provisions	309	332
Interest-bearing loans and borrowings	15,139	6,838
Contingent consideration liability	354
Lease liability	2,586
Total current liabilities	29,878	16,177
Total liabilities	46,193	34,505
Total equity and liabilities	£ 86,449	£ 67,276

Consolidated statement of cash

Consolidated statement of cash flows - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Loss before tax	£ (41,118)	£ (37,306)	£ (46,951)
Adjustments to reconcile loss before tax to net cash flows:
Depreciation of property, plant and equipment	1,577	39	36
Share-based payment expense	1,636	2,190	3,652
Net foreign exchange loss / (gain)	(483)	44	1,384
Provision for social security contributions on employee share options	(738)	(1,446)	1,116
Provision for deferred cash consideration	221	443
Interest earned	(377)	(307)	(827)
Finance charges	3,731	1,916	1,090
Modification gain on bank loan	(456)
Modification loss on bank loan		730
Gain on bargain purchase	(3,681)
Fair value remeasurement on contingent consideration	354
Working capital adjustments:
(Increase) / decrease in trade and other receivables	(936)	804	(840)
Increase / (decrease) in trade and other payables	(6,730)	1,602	3,860
Tax received	1,069	8,152	5,331
Net cash flows (used in) operating activities	(45,931)	(23,139)	(32,149)
Investing activities
Cash acquired from acquisition	10,074
Purchase of property, plant and equipment	(21)	(36)	(16)
Disposal of property, plant and equipment		2
Purchase of license			(2,280)
(Investments)/proceeds from sale of short-term investments	32,865		(2,500)
Interest earned	377	286	1,052
Net cash flows (used in)/from investing activities	43,295	252	(3,744)
Financing activities
Proceeds from issue of ordinary shares		273	15,000
Transaction costs on issue of shares	(761)	(8)	(730)
Proceeds from issue of bank loan		455	20,000
Transaction costs on bank loan		(921)	(200)
Interest paid on bank loan	(1,739)	(1,645)	(327)
Proceeds from TAP agreement		78
Purchase of treasury shares	(998)	(307)
Payment of lease liabilities	(2,212)
Net cash flows from/(used in) financing activities	(5,710)	(2,075)	33,743
Net (decrease) in cash and cash equivalents	(8,346)	(24,962)	(2,150)
Cash and cash equivalents at the beginning of the period	25,042	50,045	53,578
Effect of exchange rate changes on cash and cash equivalents	(349)	(41)	(1,383)
Cash and cash equivalents at the end of the period	£ 16,347	£ 25,042	£ 50,045

Consolidated statement of chang

Consolidated statement of changes in equity - GBP (£) £ in Thousands	Total	Share options [member]	LTIPs [member]	Deferred bonus shares [member]	Deferred equity consideration [member]	Conversion of loan note [member]	April 23, 2019 [member]	October 31, 2017 [member]	June 1, 2018 [member]	August 3, 2018 [member]	October 22, 2018 [member]	Issued capital [member]	Issued capital [member]Conversion of loan note [member]	Issued capital [member]Novartis bonus shares [member]	Issued capital [member]April 23, 2019 [member]	Issued capital [member]October 31, 2017 [member]	Issued capital [member]October 22, 2018 [member]	Share premium [member]	Share premium [member]Conversion of loan note [member]	Share premium [member]Novartis bonus shares [member]	Share premium [member]October 31, 2017 [member]	Share premium [member]June 1, 2018 [member]	Share premium [member]August 3, 2018 [member]	Share premium [member]October 22, 2018 [member]	Other capital reserves [member]	Other capital reserves [member]Share options [member]	Other capital reserves [member]LTIPs [member]	Other capital reserves [member]Deferred bonus shares [member]	Other capital reserves [member]Deferred equity consideration [member]	Other capital reserves [member]Conversion of loan note [member]	Other capital reserves [member]Novartis bonus shares [member]	Other capital reserves [member]April 23, 2019 [member]	Employee benefit trust [member]	Other reserves [member]	Own shares [Member]	Accumulated losses [member]	Translated reserve
Beginning balance at Dec. 31, 2016	£ 79,255											£ 193						£ 99,975							£ 12,666									£ 7,000		£ (40,579)
Loss for the period	(38,799)																																			(38,799)
Issue of share capital	15,000							£ 1,520				15				£ 1		14,985			£ 1,519
Issue of share capital						£ 1,399							£ 2	£ 2					£ 1,397	£ 1,081											£ (1,083)
Net fair value gain / (loss) on investments in debt instruments held at fair value (Note 25)
Share-based payments		£ 3,028	£ 298	£ 326	£ 1,331																					£ 3,028	£ 298	£ 326	£ 1,331
Conversion of convertible loan	62					£ (207)																								£ (207)						62
Transaction costs on issuance of share capital	(730)																	(730)
Ending balance at Dec. 31, 2017	62,483											213						118,227							16,359									7,000		(79,316)
Loss for the period	(32,029)																																			(32,029)
Issue of share capital									£ 150	£ 13	£ 111						£ 1					£ 150	£ 13	£ 110
IFRS 9 restatement	124																																			124
Net fair value gain / (loss) on investments in debt instruments held at fair value (Note 25)
Share-based payments			1,871	£ 319																							1,871	£ 319
Issue of warrants for TAP agreement	44																								44
Transaction costs on issuance of share capital	(8)																	(8)
Purchase of treasury shares	(307)																																£ (307)
Ending balance at Dec. 31, 2018	32,771											214						118,492							18,593								(307)	7,000		(111,221)
Loss for the period	(34,844)																																			(34,844)
Issue of share capital	2,369						£ 40,892					3			£ 74			2,366														£ 40,818
Issue of share capital												3						1,587							(1,590)
Currency translation of foreign operations	(499)																																				£ (499)
Net fair value gain / (loss) on investments in debt instruments held at fair value (Note 25)
Share-based payments		£ 1,543	£ 93																							£ 1,543	£ 93
Transaction costs on issuance of share capital	(761)																	(761)
Equity element of convertible loan	(310)																								(310)
Purchase of treasury shares	(998)																																£ (998)
Ending balance at Dec. 31, 2019	£ 40,256											£ 294						£ 121,684							£ 59,147									£ (1,305)	£ 7,000	£ (146,065)	£ (499)

Corporate information

Corporate information	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Corporate information	1. Corporate information Mereo BioPharma Group plc (the “Company”) is a clinical-stage, U.K.-based biopharmaceutical company focused on oncology and rare diseases. The Company is a public limited company incorporated and domiciled in the U.K., and registered in England, with our shares publicly traded on the Alternative Investment Market of the London Stock Exchange under the ticker symbol MPH. The Company is also listed on the Nasdaq Global Market via American Depositary Shares (“ADSs”) under the ticker symbol MREO. The Company’s registered office is located at Fourth Floor, 1 Cavendish Place, London, W1G 0QF, United Kingdom. The consolidated financial statements of Mereo BioPharma Group plc and its subsidiaries (collectively, the “Group”) for the year ended December 31, 2019 were authorized for issue in accordance with a resolution of the Directors on [April] [•], 2020]. The principal activities of the Group is the research and development of novel pharmaceutical products. On April 23, 2019, the Group completed the acquisition of OncoMed Pharmaceuticals, Inc. (“OncoMed”), a company which is based in California and was previously a public company listed on the Nasdaq Global Market in the U.S.

Significant accounting policies

Significant accounting policies	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Significant accounting policies	2. Significant accounting policies 2.1 Basis of preparation The Group’s consolidated financial statements have been prepared in accordance with International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). The financial statements are presented in pound sterling (“£’000”), which is the functional and presentational currency of the Group. All amounts disclosed in the financial statements and notes have been rounded off to the nearest thousand currency units, unless otherwise stated. 2.2 Revision of previously issued financial statements During 2019, we identified a classification error in our statement of comprehensive loss for the year ended December 31, 2018 related to loan modification expense. In correcting the error, administrative expenses reduced by £0.7 million and finance charges increased by an equivalent amount. There was no impact on net loss. We evaluated the materiality of the error quantitatively and qualitatively and concluded it was not material to our previously issued Consolidated Financial Statements as a whole for the year ended and as of December 31, 2018. Please refer to Financial statement notes 9 and 19. 2. 3 The consolidated financial information comprises the financial statements of Mereo BioPharma Group plc and its subsidiaries as at December 31, 2019. Subsidiaries are all entities over which the Group has control. The Group controls an entity when the Group is exposed to, or has rights to, variable returns from its involvement with the entity and has the ability to affect those returns through its power over the entity. Subsidiaries are fully consolidated from the date on which control is transferred to the Group. They are deconsolidated from the date that control ceases. Intercompany transactions, balances and unrealized gains on transactions between Group companies are eliminated in preparing the consolidated financial statements. Accounting policies of subsidiaries are consistent with the policies adopted by the Group. The Company has an employee share trust to facilitate share transactions pursuant to employee share schemes. Although the trust is a separate legal entity from the Group, it is consolidated into the Group’s results in accordance with the IFRS 10 rules on special purpose vehicles. The Company is deemed to control the trust principally because the trust cannot operate without the funding the Group provides. 2. 4 Management views the Group as a single portfolio of product candidates. Only research and development expenses are monitored at a product candidate level, however the Chief Operating Decision Maker (“CODM”) makes decisions over resource allocation at an overall portfolio level. The Group’s financing is managed and monitored on a consolidated basis. Following the acquisition of OncoMed during the year, non-current non-current The Group’s CODM is the executive leadership team which is comprised of several individuals including the Chief Executive Officer (“CEO”) and Chief Financial Officer (“CFO”). The executive leadership team is responsible for managing the operating results of the business. The operations of the Group are mostly influenced by the timing of progression on underlying clinical development programmes across product candidates which remain under development. 2.5 Going concern As at May 31, 2020 the group had total cash resources* £10.1 million. Taken together with the private placement which completed on June 3, 2020 and which raised net proceeds of approximately £51.4 million, the group has current total cash resources of £61.5 million. The Directors have prepared detailed cashflow forecasts for the 30-month period to December 31, 2022 based on delivering the business plan objectives set out in the strategic report which include: • Completion of the adult Phase 2b extension study for setrusumab • Completion of the current Phase 2 study for alvelestat • Commencement later in 2020 of a new Phase 1b study for etiligimab These forecasts indicate that the group has a total cash runway into 2022 and will have sufficient funds to meet its liabilities as they fall due for at least the next 12 months. In preparing these forecasts the directors have considered the impact of COVID-19 and in particular the unprecedented burden on health systems in impacted countries around the world. As a result, clinical centres have diverted resources away from the performance of clinical trials and because of that and the vulnerability of patients in the Company’s setrusumab clinical development program for osteogenesis imperfecta (OI) and its Phase 2 alvelestat program for patients with alpha-1 antitrypsin deficiency (AATD), the Company’s clinical activities will face some delays. AATD patients, in particular, are at greater risk from COVID-19 given that the condition is a respiratory and lung condition, for this reason, our Phase 2 alvelestat trial will be delayed with topline data now expected in 2021. Subject to a partnership, we are also currently planning to initiate a Phase 3 study in children with OI in late 2020, however, the initiation of the study may also be delayed. In addition, the Directors have considered a downside scenario involving an increase in operating overheads, an increase in the costs of setting up and running the planned Phase 1b study for etiligimab when this study is contracted out to third parties and increased investment in manufacturing development costs for setrusumab. In addition, In this scenario the forecasts also indicate that the group will have sufficient funds to meet its liabilities as they fall due for at least the next 12 months. In both scenarios the Directors have not taken into account potential income from partnering one or more of its assets which would increase the cash resources available to the Group In conclusion, although the Group continues to make losses, the directors believe it is appropriate to prepare the financial information on the going concern basis. This is because the Group’s development into new products continues to progress according to plan and the funding secured to date, together with the funds that have come into the Group since the year end (as described more fully in Note 30) will allow it to meet its liabilities as they fall due for at least 12 months from the date of authorization for the issue of these consolidated financial statements. • Total cash resources are a non-GAAP measure being cash and short-term deposits and short-term investments 2. 6 a) Taxes Tax expense recognized in the statement of comprehensive income comprises the sum of deferred tax and current tax not recognized in other comprehensive income or directly in equity Current income tax Current income tax assets and / or liabilities are measured at the amount expected to be recovered from or paid to the taxation authorities that are unpaid at the reporting date. Current tax is payable on taxable profit, which differs from profit or loss in the financial statements. Calculation of current tax is based on tax rates and tax laws that have been enacted or substantively enacted by the end of the reporting period within the jurisdictions that the Group operates in. Amounts receivable in respect of research and development tax credits are recognized in the financial statements provided there is sufficient evidence that the amounts are recoverable. These credits are recognized within income tax in the consolidated statement of comprehensive loss. Deferred tax Deferred tax is provided using the liability method on temporary differences between the tax bases of assets and liabilities and their carrying amounts for financial reporting purposes at the reporting date. Deferred income tax assets are recognized for all deductible temporary differences, carry-forward of unused tax credits and unused tax losses, to the extent that it is probable that taxable profit will be available against which the deductible temporary differences and the carry-forward of unused tax credits and unused tax losses can be utilized. The carrying amount of deferred income tax assets is reviewed at the end of each reporting period and reduced to the extent that it is no longer probable that sufficient taxable profit will be available to allow all or part of the deferred income tax asset to be utilized. Unrecognized deferred income tax assets are reassessed at the end of each reporting period and are recognized to the extent that it has become probable that future taxable profit will allow the deferred tax asset to be recovered. Deferred tax assets and liabilities are measured on an undiscounted basis at the tax rates that are expected to apply to the year when the asset is realized, based on tax rates (and tax laws) enacted or substantively enacted at the end of the reporting period. IFRIC 23, Uncertainty over Income Tax Treatments In June 2017, the IASB issued IFRIC Interpretation 23, Uncertainty over Income Tax Treatments (IFRIC 23), which addresses how uncertain tax positions should be accounted for under IFRS. IFRIC 23 requires that, where acceptance of the tax treatment by the relevant tax authority is considered probable, it should be assumed as an accounting recognition matter that treatment of the item will ultimately be accepted. Therefore, no tax provision would be required in such cases. However, if acceptance of the tax treatment is not considered probable, the entity is required to reflect that uncertainty using an expected value (i.e., a probability-weighted approach) or the single most likely amount. IFRIC 23 is mandatorily effective for accounting periods beginning on or after 1 January 2019 and any resulting change to the tax provisions should be recognized in retained earnings. Mereo has recognized a net tax expense of nil in retained earnings on 1 January 2019 in respect of the adoption of IFRIC 23. b) Foreign currencies Items included in the financial statements are measured using the curren cy Transactions in foreign currencies are initially recorded by the Group’s entities at the rate ruling on the date the transaction first qualifies for recognition. Differences arising on settlement or translation of monetary items are recognized in the consolidated statement of comprehensive loss, as well as gains or losses on the retranslation of foreign currency balances at the year end. The results and financial position of Group entities that have a functional currency different from the presentational currency of the Group are translated into the presentational currency (pound sterling). The assets and liabilities of such entities are translated into pound sterling at the rate of exchange ruling at the balance sheet date. Income and expenses are translated at the average rate for the period. Fair value adjustments arising on acquisition of such entities are treated as assets and liabilities of the relevant entity and translated into pound sterling at the closing rate. The exchange differences arising on translation for consolidation are recognized in other comprehensive income. c) Property, plant and equipment Property, plant and equipment is stated at cost, net of accumulated depreciation and accumulated impairment losses, if any. Such cost includes the cost of replacing part of the plant and equipment if the recognition criteria are met. All other repair and maintenance costs are recognized in profit or loss as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the assets, as follows: • Leasehold improvements ten years • Office equipment five years • IT equipment three years The right-of-use property, plant and equipment. Right-of-use • Right-of-use asset (building) six to nine years • Right-of-use asset (equipment) one to two years An item of property, plant and equipment and any significant part initially recognized is derecognized upon disposal or when no future economic benefits are expected from its use or disposal. Any gain or loss arising on derecognition of the asset (calculated as the difference between the net disposal proceeds and the carrying amount of the asset) is included in the statement of comprehensive loss when the asset is derecognized. The residual values, useful lives and methods of depreciation of property, plant and equipment are reviewed at each financial year end and adjusted prospectively, if appropriate. d) Business combinations Business combinations are accounted for using the acquisition method of accounting. At the date of the acquisition, the Group initially recognizes the fair value of the identifiable assets acquired, the liabilities assumed and any non-controlling interest in the acquired business. The consideration transferred is measured at fair value at the date acquisition. The excess of the consideration transferred over the fair value of net identifiable assets of the business acquired is recorded as goodwill, unless the amount of consideration transferred is less than the fair value of net identifiable assets of the business acquired in which case the difference is recognized directly in the consolidated statement of comprehensive loss as a bargain purchase. A valuation is performed of assets and liabilities assumed on each acquisition accounted for as a business combination based on our best estimate of fair value. Where the settlement of any part of cash consideration is deferred, the amounts payable in the future are discounted to their present value. Contingent consideration is classified either as equity or a financial liability and is recognized at fair value on the acquisition date. Amounts classified as a financial liability are subsequently remeasured to fair value in accordance with IFRS 9 (Financial Instruments), with changes in fair value recognized in the consolidated statement of comprehensive loss as an administrative expense. Directly attributable acquisition-related costs are expensed as incurred within the consolidated statement of comprehensive loss. d) Leases (IFRS 16) Effective January 1, 2019, the Group implemented IFRS 16 (Leases). IFRS 16 (Leases) replaces existing guidance, including IAS 17 ( L For further information, refer to Note 4. e) Intangible assets Intangible assets are initially recorded at cost which has been determined as the fair value of the consideration paid and payable. Assets that have been acquired through a business combination are initially recorded at fair value. The fair value of consideration is regularly reviewed based on the probability of achieving contractual milestones. Intangible assets are reviewed for impairment at each reporting date by allocating the assets to the cash-generating units to which they relate. The estimated useful life is the lower of the legal duration and economic useful life. The estimated useful lives of intangible assets are regularly reviewed on an at least annual basis. Where the consideration paid or payable is in shares, the cost is measured in accordance with IFRS 2 (Share Based Payments). Amortization would commence when product candidates underpinned by the intangible asset become available for commercial use. No amortization has been charged to date, as the product candidates underpinned by the intellectual property rights are not yet available for commercial use. f) Financial instruments Financial assets and liabilities are recognized in the consolidated balance sheet only when the Group becomes party to the contractual provisions of the instrument. Financial assets On initial recognition, a financial asset is classified into one of three primary measurement categories: • Amortized cost; • Fair value through OCI (“FVOCI”); or • Fair value through profit or loss (“FVTPL”). The initial classification into a primary measurement category depends on the nature and purpose of the financial asset. For each reporting period covered herein, the Group’s financial assets were restricted to financial assets held at FVOCI. This relates to short-term investments which are not classified as cash and short-term deposits and are held in a business model whose objective is achieved by both collecting contractual cash flows and selling the short-term investment on maturity. For short-term investments, interest income and impairment gains or losses are recognized directly in the consolidated statement of comprehensive loss. The difference between cumulative fair value gains or losses and the cumulative amounts recognized in the consolidated statement of comprehensive loss is recognized in other comprehensive income until derecognition, when the amounts in other comprehensive income are reclassified to the consolidated statement of comprehensive loss. g) Fair value measurement Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value measurement is based on the presumption that the transaction to sell the asset or transfer the liability takes place either: • In the principal market for the asset or liability; or • In the absence of a principal market, in the most advantageous market for the asset or liability. The principal or the most advantageous market must be accessible by the Group. The fair value of an asset or a liability is measured using the assumptions that market participants would use when pricing the asset or liability, assuming that market participants act in their economic best interest. The Group uses valuation techniques that are appropriate in the circumstances and for which sufficient data are available to measure fair value, maximizing the use of relevant observable inputs and minimizing the use of unobservable inputs. All assets and liabilities for which fair value is measured or disclosed in the financial statements are categorized within the fair value hierarchy, described as follows, based on the lowest level input that is significant to the fair value measurement as a whole: • Level 1 — quoted (unadjusted) market prices in active markets for identical assets or liabilities. • Level 2 — valuation techniques for which the lowest level input that is significant to the fair value measurement is directly or indirectly observable. • Level 3 — valuation techniques for which the lowest level input that is significant to the fair value measurement is unobservable. For assets and liabilities that are recognized in the financial statements on a recurring basis, the Group determines whether transfers have occurred between levels in the hierarchy by reassessing categorization (based on the lowest level input that is significant to the fair value measurement as a whole) at the end of each reporting period. h) Impairment of non-financial Further disclosures relating to impairment of non-financial • Disclosures for significant assumptions Note 3 • Property, plant and equipment Note 12 • Intangible assets not yet available for use Notes 13 and 14 The Group assesses, at each reporting date, whether there is an indication that an asset may be impaired. If any indication exists, or when annual impairment testing for an asset is required, the Group estimates the asset’s recoverable amount. An asset’s recoverable amount is the higher of an asset’s or cash-generating unit’s fair value less costs of disposal and its value in use. The recoverable amount is determined for an individual asset, unless the asset does not generate cash inflows that are largely independent of those from other assets or groups of assets. When the carrying amount of an asset or cash-generating unit exceeds its recoverable amount, the asset is considered impaired and is written down to its recoverable amount. In assessing value in use, the estimated future cash flows are discounted to their present value using a pre-tax Impairment losses are recognized in the statement of comprehensive loss in expense categories consistent with the function of the impaired asset. An assessment is made at each reporting date to determine whether there is an indication that previously recognized impairment losses no longer exist or have decreased. If such indication exists, the Group estimates the asset’s or cash-generating unit’s recoverable amount. A previously recognized impairment loss is reversed only if there has been a change in the assumptions used to determine the asset’s recoverable amount since the last impairment loss was recognized. The reversal is limited so that the carrying amount of the asset does not exceed its recoverable amount, nor exceed the carrying amount that would have been determined, net of depreciation, had no impairment loss been recognized for the asset in prior years. Such reversal is recognized in the statement of comprehensive loss unless the asset is carried at a revalued amount, in which case the reversal is treated as a revaluation increase. i) Cash and short-term deposits Cash and short-term deposits in the balance sheet comprise cash at banks and on hand and short-term deposits with a maturity of three months or less, which are subject to an insignificant risk of changes in value. j) Short-term investments Cash held on deposit for terms greater than three months are recognized at fair value in the balance sheet with fair value changes recognized in other comprehensive income. Interest revenue, impairment gains and losses, and a portion of foreign exchange gains and losses, are recognized in profit and loss. When the short-term investment is derecognized or reclassified, changes in fair value previously recognized in other comprehensive income and accumulated in equity are reclassified to profit and loss. k) Provisions Provisions are recognized when the Group has a present obligation (legal or constructive) as a result of a past event, it is probable that an outflow of resources embodying economic benefits will be required to settle the obligation and a reliable estimate can be made of the amount of the obligation. When the Group expects some or all of a provision to be reimbursed, for example, under an insurance contract, the reimbursement is recognized as a separate asset, but only when the reimbursement is virtually certain. The expense relating to a provision is presented in the statement of comprehensive loss net of any reimbursement. If the effect of the time value of money is material, provisions are discounted using a current pre-tax l) Share-based payments Employees (including executives) of the Group receive remuneration in the form of share-based payments, whereby employees render services as consideration for equity instruments (equity settled transactions). Incentives in the form of shares are provided to employees under various plans (Note 26). Executive officer have outstanding shares under a deferred bonus share plan (“DBSP Plan”) and a long-term incentive plan (“LTIP Plan”). In accordance with IFRS 2 Share-based Payment (“IFRS 2”), charges for these incentives are expensed through the consolidated statement of comprehensive loss on a straight-line basis over their vesting period, based on the Group’s estimate of shares that will eventually vest. The total amount to be expensed is determined by reference to the fair value of the options or awards at the date they were granted. For LTIP shares, the fair value on grant date excludes the impact of any non-market vesting conditions – these are instead taken into account by adjusting the number of equity instruments included in the measurement of the share-based payment transaction and are adjusted each period until such time as the equity instruments vest. Share options awarded to non-employees are accounted for as options awarded to employees as the value of non-employee services could be readily determined. In accordance with IFRS 2, the cancellation of share options is accounted for as an acceleration of the vesting period and therefore any amount unrecognized that would otherwise have been charged in future accounting periods is recognized immediately. When options are forfeited, the accounting expense for any unvested awards is reversed. Purchases, where consideration is satisfied by issuing equity shares, is accounted for as equity settled share-based payment transactions in accordance with IFRS 2. Fair value is determined by the share price at the date of purchase. m) Costs of issuing capital Incremental costs incurred and directly attributable to the offering of equity securities are deducted from the related proceeds of the offering. The net amount is recorded as share premium in the period when such shares are issued. Where such expenses are incurred prior to the offering they are recorded in prepayments until the offering completes. Other costs incurred in such offerings are expensed as incurred and included in general and administrative expenses. n) Convertible loan instrument Convertible loan notes are regarded as compound instruments consisting of a liability component and an equity component. At the date of issue, the fair value of the liability component is estimated using a discount rate for an equivalent liability without the conversion feature. The difference between the proceeds of issue of the convertible loan note and the fair value assigned to the liability component is included in equity. o) Employee Benefit Trust The Group operates an Employee Benefit Trust (“EBT”), the Mereo BioPharma Group plc Employee Benefit Trust. The EBT has been established to fulfil awards made under the DBSP Plan and the LTIP Plan. The EBT is a Jersey-based trust which is funded by a loan from the Company, which it will utilize to buy shares at nominal value from the Company in sufficient quantity to fulfil the envisaged awards. The EBT will acquire shares in the Company and these will be deducted from the shareholders’ funds on the consolidated balance sheet at the cost of acquisition less proceeds on disposal. Shares held by the EBT are included in the consolidated balance sheet as a reduction in equity. The Group treats the EBT as an extension of the Group and the Company as it is ultimately controlled by the Company and therefore consolidated. p) R&D costs Expenditure on product development is capitalized as an intangible asset and amortized over the expected useful economic life of the product candidate concerned. Capitalization commences from the point at which technical feasibility and commercial viability of the product candidate can be demonstrated and the Group is satisfied that it is probable that future economic benefits will result from the product candidate once completed. Capitalization ceases when the product candidate receives regulatory approval for launch. No such costs have been capitalized to date. Expenditure on R&D activities that do not meet the above criteria, including ongoing costs associated with acquired intellectual property rights and intellectual property rights generated internally by the Group, is charged to the statement of comprehensive loss as incurred. Intellectual property and in-process R&D from asset acquisitions are recognized as intangible assets at cost. q) Provision for deferred cash consideration Provision for deferred cash consideration consists of future payments which are contractually committed but not yet certain. In respect of products which are not yet approved, such deferred cash consideration excludes potential milestones, royalties or other payments that are deemed to be so uncertain as to be unquantifiable. Deferred cash consideration is recognized as a liability with the amounts calculated as the risk adjusted net present value of anticipated deferred payments. The provision is reviewed at each balance sheet date and adjusted based on the likelihood of contractual milestones being achieved and therefore the deferred payment being settled. Increases in the provision relating to changes in the probability are recognized as an intangible asset. Increases in the provision relating to the unwinding of the time value of money are recognized as a finance expense. r) Bank loan Borrowings (including interest-bearing loans) are initially recognized at fair value, net of transaction costs incurred. Borrowings are subsequently measured at amortized cost. Any difference between the proceeds (net of transaction costs) and the redemption amount is recognized in profit or loss over the period of the borrowings using the effective interest method. Under the effective interest method, amortization is included as a finance charge in the consolidated statement of comprehensive loss. The Group’s policy is to account for non-substantial modifications to financial liabilities measured at amortized cost through a gain or loss which is recorded in the consolidated statement of comprehensive loss. The gain or loss is calculated as the difference between the original contractual cash flows and the modified cash flows, discounted at the original effective interest rate. For substantial modifications, the Group’s policy is to derecognize the existing financial liability and in turn recognize a new financial liability. Borrowings are removed from the balance sheet when the obligation specified in the contract is discharged, cancelled or expired. s) Associated warrants The Group has issued certain warrant instruments to its lenders (Note 19). As the terms of the warrant instruments allow for a cashless exercise, the Group’s policy is to account for the associated warrant instruments at fair value with changes in the fair value recognized in the consolidated statement of comprehensive loss (see Note 21). t) The Alpha-1 Project (TAP) funding agreement and associated warrants The agreement is accounted for as a compound instrument which includes both debt and equity components. The liability is measured first at fair value and the residual value allocated to the equity component. The difference between the funding payment amount received and the measurement of the liability will be allocated to the warrants and recognized in equity. The value of warrants in equity will not be subsequently remeasured as the warrants will be settled by providing a fixed number of shares for a fixed amount of cash.

Significant judgments, estimate

Significant judgments, estimates and assumptions	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Significant judgments, estimates and assumptions	3. Significant judgments, estimates and assumptions The preparation of these financial statements requires the management of the Group to make estimates and judgments that affect the reported amounts of assets, liabilities, revenues and expenses. The Group bases its estimates and judgments on historical experience and on various other assumptions that it considers to be reasonable. Actual results may differ from these estimates under different assumptions or conditions. 3.1 Judgments a) Share-based compensation Incentives in the form of shares are provided to employees under certain equity award plans (which consist of both share awards and option grants). The fair value of the employee services received in exchange for equity award plans is recognized as an expense. The expense is based upon a number of assumptions disclosed in Note 26. The selection of different assumptions in the measurement of fair value of the equity award plans could affect the results of the Group. b) Business combination On April 23, 2019, the Group obtained a 100% controlling interest in OncoMed, a Company based in the U.S. which was previously listed on the Nasdaq Global Market. Judgement is applied under IFRS 3 (Business Combinations) in determining whether a transaction meets the definition of a business combination, and so accounted for in accordance with its requirements. In applying this judgement, management has considered the underlying economic substance of the transaction in addition to the contractual terms. Our assessment is that OncoMed meets the definition of a ‘business’ and the transaction has therefore been accounted for as a business combination. Please refer to Note 5 for further details regarding the OncoMed acquisition. c) Impairment of intangible assets and property, plant and equipment An assessment was made in respect of indicators of impairment in the carrying value of the Group’s intangible assets (see Note 14), right-of-use If such an indication exists, the recoverable amount of the asset, being the higher of the asset’s fair value less costs to sell and value in use, is compared to the asset’s carrying value. Any excess of the asset’s carrying value over its recoverable amount is expensed to the income statement. The assessment of intangible assets involves a number of significant judgments regarding the likelihood of successful product approval, the costs of reaching approval, the estimated useful life of intangible assets following commercialization and the subsequent commercial profitability of the product once approved. d) IFRS 16 (Leases) discount rate Following the adoption of IFRS 16 (Leases) on January 1, 2019, the Group is required discount future lease payments using the interest rate implicit in the lease, or, if that rate cannot be readily determined, the incremental borrowing rate. IFRS 16 (Leases) defines the incremental borrowing rate as the rate of interest a lessee would have to pay to borrow over a similar term, and with a similar security, the funds necessary to obtain an asset of similar value to the right-of-use For the year ended December 31, 2019, the determination of an appropriate discount rate has a significant effect on the lease liabilities recognized (see Note 4). For the current lease portfolio, the Group has determined an incremental borrowing rate based on relevant and available information as the interest rate implicit in the lease arrangements cannot be readily determined. In addition to the determination of an appropriate discount rate, the Group was also required to assess the lease term for qualifying leases. The determination of the lease term is judgmental as for certain qualifying leases held by the Group, the contract includes an extension option beyond the non-cancellable period for which the Group has the right to use the underlying asset. In applying this judgment, the Group considered the period over which it was reasonably certain to make use of the extension option. 3.2 Estimates a) Fair value of intangible assets acquired in business combination The Group performed a full valuation of the fair value of assets acquired and liabilities assumed following the acquisition of OncoMed. Based on the assets acquired and liabilities assumed, specific consideration was applied to the valuation of the intangible asset acquired which required an estimation of the expected useful life and future cash flows of the intangible asset alongside the determination of an appropriate discount rate. The intangible asset acquired was valued using a risk adjusted net present value model. b) Contingent consideration The Group makes provision for the estimated fair value of amounts payable to the former shareholders of OncoMed under the Contingent Value Rights Agreement (“CVR”), which is accounted for as a contingent consideration liability. At December 31, 2019, the Group estimates the fair value of the contingent consideration liability to be £0.4 million ($0.5 million), which is an increase from £nil on the date of acquisition (see Note 5). The increase in the fair value of the contingent consideration liability reflects the terms subsequently agreed with Oncologie, Inc. (“Oncologie”) with respect to the global licensing agreement of navicixizumab (“Navi”) (see Note 30). Total potential payments under the CVR on a gross, undiscounted basis, are approximately $80.0 million (see Note 5 The estimated contingent consideration payable is based on a risk-adjusted, probability-based scenario. Under this approach the likelihood of future payments being made to the former shareholders of OncoMed under the CVR is considered. The estimate could materially change over time in line with the development plan and subsequent commercialization of the Navi product. c) Deferred license consideration Deferred consideration in the form of cash is recognized as a provision at each balance sheet date, to the extent its amount is quantifiable at the inception of the arrangement (see Note 20). The amount provided is based on a number of estimates regarding the timing and progress of the related research. Deferred consideration in the form of shares is recognized as a share-based payment when it is probable that shares will be transferred.

Changes in accounting policies

Changes in accounting policies	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Changes in accounting policies	4. Changes in accounting policies 4.1 Changes in accounting policies 2019 Effective January 1, 2019, the Group has adopted IFRS 16 (Leases). IFRS 16 (Leases) replaces existing guidance, including IAS 17 (Leases), and sets out the principles for the recognition and measurement of leases. The new standard has resulted in an increased volume of disclosure information within these consolidated financial statements. The Group has also implemented other minor amendments to existing standards and interpretations, which have no material impact on the Group’s overall results and financial position. a) General impact of application of IFRS 16 (Leases) The date of initial application of IFRS 16 for the Group is January 1, 2019. The Group has applied IFRS 16 using the modified retrospective approach, without restatement of the comparative information. IFRS 16 introduces new or amended requirements with respect to lease accounting. It introduces significant changes to the lessee accounting by removing the distinction between operating and finance lease, requiring the recognition of a right-of-use b) Definition of a lease Previously, the Group determined at contract inception whether an arrangement was or contained a lease under IFRIC 4 (Determining Whether an Arrangement contains a Lease). The Group now assesses whether a contract is or contains a lease based on the new definition of a lease under IFRS 16 (Leases). Under IFRS 16 (Leases), a contract is or contains a lease, if the contract conveys a right to control the use of an identified asset in exchange for consideration. On transition to IFRS 16 (Leases), the Group elected to apply the practical expedient to grandfather the assessment of which transactions are leases. It applied IFRS 16 (Leases) only to contracts that were previously identified as leases. Contracts that were not identified as leases under IAS 17 and IFRIC 4 were not reassessed. In preparation for the first-time application of IFRS 16, the Group has carried out an implementation project. The new definition in IFRS 16 will not significantly change the scope of contracts that meet the definition of a lease for the Group. At inception or on reassessment of a contract that contains a lease component, the Group allocates the consideration in the contract to each lease and non-lease c) Practical expedients adopted on transition Certain practical expedients permitted by IFRS 16 are used by the Group, notably: 1) To not reassess, upon transition, whether an existing contract contains a lease (grandfather the previous assessment of whether a transaction was a lease under IAS 17 or IFRIC 4). The definition of a lease under IFRS 16 has been applied only to contracts entered into or changed on or after January 1, 2019; 2) The recognition exemptions for short-term leases (less than 12 months of lease term) and the leases of low-value 3) Used hindsight when determining the lease term, if the contract contains options to extend or terminate the lease. d) Financial impact The application of IFRS 16 to leases previously classified as operating leases under IAS 17 resulted in the recognition of right-of-use The table below sets out the adjustments recognized at the date of initial application of IFRS16, which does not include the leases acquired as part of the OncoMed acquisition. As at Impact of Restated as January 1, Non-current Property, plant and equipment 149 2,552 2,701 Prepayments and other 1,067 (50 ) 1,017 Total impact on assets 2,502 Current liabilities Trade and other payables 4,570 — 4,570 Lease liabilities — 607 607 Non-current Lease liabilities — 1,927 1,927 Accruals 4,437 (32 ) 4,405 Total impact on liabilities (2,502 ) Total impact on retained earnings — As at January 1, 2019, right-of-use Following the acquisition of OncoMed on April 23, 2019, the Group acquired an additional right-of-use The table below presents a reconciliation from operating lease commitments disclosed as at December 31, 2018 to lease liabilities recognized as at January 1, 2019. Operating lease commitments disclosed under IAS 17 (at December 31, 2018) 536 Effect of discounting (944 ) Reassessment of lease term under IFRS 16 2,942 Lease liabilities recognised under IFRS 16 (at January 1, 2019) 2,534 Certain lease agreements include an option which allows the Group to extend the lease. The Group is reasonably certain that it will invoke the extension option on the lease of medical equipment used in ongoing clinical trials, as the Group expects that the studies will extend beyond the initial lease term. Where the Group is reasonably certain that the lease will be extended, the cash flows are included in the calculation of the lease liability. The adoption of IFRS 16 (Leases) results in a decrease in other operating expenses in the consolidated statement of comprehensive loss where lease payments were previously recorded. IFRS 16 (Leases) results in an increase in depreciation and interest expense going forwards following the recognition of a right-of-use The weighted average incremental borrowing rate applied to lease liabilities recognized on transition was 15.0%. As at December 31, 2019, in relation to leases under IFRS 16 ( Leases ) the Group has recognized the following amounts in the consolidated statement of comprehensive loss: Depreciation 1,505 Interest expense 1,314 Foreign exchange gain 29 Income from sub-leasing right-of-use 855 For the year ended December 31, 2019, within the consolidated statement of cash flows under IFRS 16 (Leases) the Group has opted to disclose both the cash paid for the interest portion and cash payments for the principal portion of the lease liability as part of financing activities. The adoption of IFRS 16 (Leases) did not have an impact on net cash flows. The total cash outflow for leases amounted to £2.2 million during the year (2018: £0.3 million). e) Subsequent updates As at December 31, 2019, the lease term remaining on the medical equipment has been reassessed in line with the contractual agreement. The reassessment of lease term has been accounted for as a change in accounting estimate and the lease liability has been remeasured accordingly to reflect the change in estimated future lease payments. The carrying amount of the right-of-use 4.2 Changes in accounting policies 2018 Effective January 1, 2018, the Group has adopted IFRS 9 (Financial Instruments) which introduces new requirements for: 1. The classification and measurement of financial assets and financial liabilities; 2. Impairment for financial assets; 3. General hedge accounting; and 4. New accounting for certain modifications and exchanges of financial liabilities measured at amortized cost. The only impact on the Group is in relation to the non-substantial In relation to the non-substantial At January 1, 2018 ( as calculated under IAS 39) 1,977 Amounts restated through retained earnings (124 ) At January 1, 2018 (as calculated under IFRS 9) 1,853 The Group has considered the adoption of IFRS 9 on receivables and determined the expected credit loss to be immaterial, and therefore no adjustment has been made for this.

Acquisition of subsidiary

Acquisition of subsidiary	12 Months Ended
	Dec. 31, 2019
Disclosure of detailed information about business combination [abstract]
Acquisition of subsidiary	5. Acquisition of subsidiary On April 23, 2019, the Group obtained control of OncoMed, a Company based in the U.S., which was previously l 100 per cent of its issued share capital. OncoMed is a clinical-stage biopharmaceutical company focused on discovering and developing novel therapeutics that address the fundamental biology driving cancer’s growth, resistance, recurrence and metastasis. OncoMed was acquired in order to broaden the Group’s asset base, strengthen its cash position and obtain a US listing to diversify international shareholder base of the combined group. The final acquisition accounting is set out below: OncoMed Cash and short-term deposits 10,074 Short-term investments 29,019 Other receivables 155 Prepayments 1,699 Property, plant and equipment 82 Right-of-use 10,755 Identifiable intangible assets 12,693 Other liabilities (9,215 ) Lease liabilities (10,689 ) Net identifiable assets 44,573 Bargain purchase (3,681 ) Total consideration 40,892 Equity instruments (24.8 million ordinary shares) 40,892 Contingent consideration arrangement — Total consideration 40,892 The Group acquired net cash of £10.1 million with the acquisition of OncoMed, being the value of the cash and short-term deposits on April 23, 2019. The fair value of the 24.8 million ordinary shares issued as the consideration paid for OncoMed was measured based on the Group’s quoted share price on April 23, 2019 . As the Group acquired OncoMed for an amount less than the fair market value of the net assets acquired, a gain on bargain purchase of £3.7 million was realized. The was attributable to the following factors: • Subject to working capital adjustments, the immediately pre-closing 90-day • In the period from announcement of the deal and the date of acquisition (April 23, 2019), a period of approximately five months, OncoMed continued to generate losses, reflecting continue research and development activity, together with recurring expenditure on its overheads. This had the effect of reducing net assets acquired on the acquisition date compared with net assets at the time the acquisition was agreed. Additional cash consideration, accounted for as contingent consideration, becomes payable under a Contingent Value Rights Agreement (“CVR”) relating to OncoMed’s etigilimab (“TIGIT”) and navicixizumab (“Navi”) products. The contingent consideration would become payable upon the achievement of certain milestones in the future specific to TIGIT (“the TIGIT milestone”) and Navi (“the Navi milestone”).. As at the date of acquisition the fair value of the contingent consideration was estimated to be close to £nil. In making that assessment, the following information and factors were considered: 1) The uncertain outcomes of current clinical studies; 2) The level of uncertainty regarding the availability of future funding partners; 3) The level of uncertainty relating to the success of future development of such products; and 4) The dependency of the CVR milestones on the occurrence of events that are outside of the control of the Group; and 5) The likelihood of Celgene exercising the exclusive option granted by OncoMed to Celgene in relation to OncoMed’s TIGIT product, particularly given Bristol-Myers Squibb’s proposed acquisition of Celgene. In June 2019 it was announced that Celgene had decided, in light of strategic product portfolio considerations, not to exercise its option to license TIGIT. Accordingly, the TIGIT milestone can no longer be achieved. As at December 31, 2019, the Group estimates the fair value of the Navi milestone to be £0.4 million ($0.5 million) which is accounted for as a contingent consideration liability, (see Note 25 and Note 30). The maximum undiscounted amount of the Navi milestone is subject to an aggregate cap of $80 million. The fair value of the financial assets includes receivables from the landlord under OncoMed’s office lease arrangement in relation to tenant improvements with a fair value and a gross contractual value of £0.2 million. It is estimated at acquisition date that all contractual cash flows are collectable in full. Short-term investments acquired with OncoMed were treasury bills (recognized at fair value through other comprehensive income), in line with the Group’s accounting policy (see Note 25). Acquisition related costs (presented net against the gain on bargain purchase in the consolidated statement of comprehensive loss) amounted to £2.6 million (rounded). Transaction costs incremental and directly attributable to the issuance of new share capital associated with the acquisition of OncoMed amounted to £0.8 million, which is accounted for within equity. The net gain on bargain purchase in the consolidated statement of comprehensive loss is therefore £1.0 million (rounded). OncoMed contributed £nil revenue and £5.7 million to the Group’s loss for the period between the date of acquisition and the balance sheet date. If the acquisition of OncoMed had been completed on the first day of the financial year, group revenues for the period would have been £3.3 million and the Group’s loss would have been £42.9 million. This information is provided for illustrative purposes only and is not necessarily indicative of the results that the Group would have occurred had OncoMed been acquired at the beginning of the year, or indicative of future results of the Group.

Group information

Group information	12 Months Ended
	Dec. 31, 2019
Investments accounted for using equity method [abstract]
Group information	6. Group information Information about subsidiaries The consolidated financial statements of the Group include: Name Principal activities Country of % equity December 31, 2019 % equity Mereo BioPharma 1 Limited Pharmaceutical R&D U.K. 100 100 Mereo BioPharma 2 Limited Pharmaceutical R&D U.K. 100 100 Mereo BioPharma 3 Limited Pharmaceutical R&D U.K. 100 100 Mereo BioPharma 4 Limited Pharmaceutical R&D U.K. 100 100 Mereo BioPharma Ireland Limited Pharmaceutical R&D Ireland 100 100 OncoMed Pharmaceuticals, Inc. Pharmaceutical R&D U.S. 100 — Navi Subsidiary, Inc. Pharmaceutical R&D U.S. 100 — Mereo US Holdings Inc. Holding company U.S. 100 100 Mereo MergerCo One Inc. Holding company U.S. — 100 Mereo BioPharma Group plc Employee Benefit Trust Employee share scheme Jersey — — The registered office of Mereo BioPharma 1 Limited, Mereo BioPharma 2 Limited, Mereo BioPharma 3 Limited and Mereo BioPharma 4 Limited is located at Fourth Floor, 1 Cavendish Place, London W1G 0QF. The registered office of Mereo BioPharma Ireland Limited is 25/28 North Wall Quay, Dublin 1 D01H104, Ireland. Mereo US Holdings Inc. and Mereo MergerCo One Inc. were incorporated on December 3, 2018 for the sole purpose of effecting the business combination with OncoMed (see Note [5]). Following the business combination with OncoMed, Mereo MergerCo One Inc. ceased to exist. The registered office of Mereo US Holdings Inc. is 251 Little Falls Drive, City of Wilmington, County of New Castle, Delaware 19808, U.S. Mereo MergerCo One Inc. was a 100% owned subsidiary of Mereo US Holdings Inc. OncoMed became a wholly owned subsidiary of Mereo US Holdings Inc. on April 23, 2019 and is therefore an indirect, wholly owned subsidiary of Mereo BioPharma Group plc. The registered office of OncoMed Pharmaceuticals, Inc. is 251 Little Falls Drive, City of Wilmington, Country of New Castle, Delaware 19808, U.S. Navi Subsidiary, Inc, incorporated on April 15, 2019, is a wholly owned subsidiary of OncoMed. Under IFRS, the Employee Benefit Trust is treated as an extension of the Group and the Company as it is controlled and therefore consolidated.

Loss before taxation

Loss before taxation	12 Months Ended
	Dec. 31, 2019
Schedule Of Detailed Information About Loss Before Taxation [Abstract]
Loss before taxation	7. Loss before taxation Loss before tax is stated after charging: Year ended December 31, 2018 Year ended 9 Fees payable to the Company’s Auditor for the audit of Group accounts 323 514 Fees payable to the Company’s Auditor for other services: Audit of subsidiary accounts 30 45 Audit-related assurance services 171 311 Accounting advisory services 10 — Legal and professional fees including patent costs 936 2,413 Operating lease expense (IAS 17) 293 — Depreciation of right-of-use — 1,505 Depreciation (excluding right-of-use 40 52 Following the adoption of IFRS 16 (Leases) on January 1, 2019, the Group has recognized right-of-use recognized

Employees

Employees	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Employees	8. Employees The average monthly number of persons employed by the Group (including Directors) during the year was: Year ended 8 Year ended 9 By activity Administrative 24 28 Research and development 12 18 Total 36 46 Total compensation costs for persons employed by the Group (including Directors) during the year was: Year ended 8 Year ended 9 Included in research and development expenses: Salaries 1,792 2,824 Social security costs (30 ) 110 Pension contributions 73 62 Share-based payment expense 526 152 Included in administrative expenses: Salaries 2,903 3,384 Social security costs (828 ) (124 ) Pension contributions 99 114 Share-based payment expense 1,663 1,485 Total employee benefits expense 6,198 8,007 Total compensation costs for Directors during the year was: Year ended 8 Year ended 9 Salaries and fees 1,047 1,106 Benefits in kind 15 17 Pension contributions 11 25 Bonus 512 294 Total 1,585 1,442 During 2019, two Directors were member s Further details concerning the remuneration of Key Management Personnel can be found in Note 28.

Other income _ expenses and adj

Other income / expenses and adjustments	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Other income / expenses and adjustments	9. Other income / expenses and adjustments 9.1 Finance income Year ended December 31 2017 2018 2019 Bank interest earned 827 307 42 Interest earned on short-term investments — — 141 Gain on short-term investments — — 194 Total finance income 827 307 377 9.2 Finance charge Year ended December 31 2017 2018 2019 Interest payable on convertible loan (103 ) (185 ) (20 ) Interest on TAP funding — — (10 ) Interest payable on bank loan (327 ) (1,645 ) (1,739 ) Interest on lease liabilities — — (1,314 ) Accreted interest on bank loan (67 ) (782 ) (1,523 ) Transaction costs on bank loan (200 ) — — Modification (loss)/gain on bank loan — (730 )* 456 Loss on short-term deposits (339 ) (22 ) — Discounting of provision for deferred cash consideration — (443 ) (221 ) Change in warrant fair value (54 ) 716 875 Total finance charge (1,090 ) (3,091 ) (3,496 ) * We have reclassified the loan modification loss occurring in 2018 resulting in the reduction of administrative expenses by £0.7 million, and the increase in finance charges of an equivalent amount. Please refer

Income tax

Income tax	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Income tax	10. Income tax Year ended December 31 201 7 201 8 201 9 U.K. corporation tax R&D credit 8,152 5,277 5,149 Other tax income / (expense) — — 1,125 Income tax credit 8,152 5,277 6,274 U.K. income tax The Group is entitled to claim tax credits in the U.K. under the U.K. R&D small or medium-sized U. S On December 22, 2017, the Tax Cuts and Jobs Act were entered into law. Following the acquisition of OncoMed during the year, the Group has analyzed the effects of the tax reform for the financial year ended December 31, 2019. The new tax law permanently repeals the corporate Alternative Minimum Tax (“AMT”) and provides a transition period where existing AMT credits are refundable. Other tax income of £1.1 million reflects amounts received or receivable by the Group as AMT credits. As at December 31, 2019, £1.0 million is receivable, recognized as other taxes recoverable within the consolidated balance sheet. At December 31, 2019, the Group had an Uncertain Tax Position of £2.5m being held off the Balance Sheet, in respect of the R&D tax credits in the US. The Uncertain Tax Position is calculated based upon historic US R&D claims and equates to around 20% of the outstanding US R&D claims. Reconciliation of effective tax rate Year-ended December 31, 2017 2018 2019 Loss on ordinary activities before income tax (46,951 ) (37,306 ) (41,118 ) Loss on ordinary activities before tax at the U.K.’s statutory income tax rate of 19% (2018: 19%) 9,038 7,088 7,812 Expenses not deductible for income tax purposes (permanent differences) (13 ) (1,070 ) (317 ) Temporary timing differences (712 ) (277 ) (343 ) R&D relief uplift 3,447 2,271 2,540 Losses (unrecognized) (3,785 ) (2,804 ) (4,380 ) Deferred income from MBG loan guarantee costs 177 69 (54 ) Differences in overseas tax rates — — 340 Gain on bargain purchase — — 699 Other — — (23 ) Tax credit for the year 8,152 5,277 6,274 Deferred tax The analysis of unrecognized deferred tax is set out below: December 31, 2017 2018 2019 Losses 6,121 8,604 19,443 US tax credits — — 10,032 Accruals — — 947 Fixed assets — — 400 Other — 6 202 Temporary differences trading 2,267 495 4 Net deferred tax asset (unrecognised) 8,388 9,105 31,028 The analysis of recognized deferred tax is set out below: At Acquisition Recognized At Deferred tax liabilities Intangible asset — (2,686 ) — (2,686 ) Deferred tax asset Net operating losses — — 2,686 2,686 Net deferred tax asset/(liability) — (2,686 ) 2,686 — The deferred tax liability has arisen from the recognition of separately identifiable intangible assets on the acquisition of OncoMed (see Note 5). A deferred tax asset on losses has been recognized up to the level of the deferred tax liability, resulting in a net iability of £nil. The remaining deferred tax assets, as set out in the table above, have not been recognized as there is uncertainty regarding when suitable future profits against which to offset the accumulated tax losses will arise. U.K. deferred tax A reduction in the rate of UK tax to 19% from April 1, 2017 and to 17% from April 1, 2020 was at the Balance Sheet date. However subsequently, the UK Government announced that the UK corporation tax rate would remain at 19% and not reduce to 17% on 1 April 2020. This was substantively enacted on 17 March 2020. The standard rate of UK corporation tax applied to reported loss is 19% (201 8 . Unrecognized U K deferred tax assets and liabilities are calculated at a rate of %, There is no expiration date for accumulated tax losses in the U.K. entities. At December 31, 2019, the Group had U.K. tax losses to be carried forward of approximately £70.2 million (2018: £50.0 million). U. S In the U.S., the Tax Cuts and Jobs Act reduced the corporation tax rate to 21% from January 1, 2018. The effect of the new U.S. corporation tax rate has been considered in these financial statements. U.S. deferred tax assets and liabilities are calculated at a blended approximately For Onco M accumulated tax losses carried forward prior to the acquisition of the Company, there is a change of control restriction which will limit the amount available in any one year. At December 31, 2019, the Group had U .S. federal , of wh ich £40.9 million can be carried will At December 31, 2019, the Group had U.S. state 3.2 million which begin to expire in 2028 .

Loss per share

Loss per share	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Loss per share	11. Loss per share Basic loss per share is calculated by dividing the loss attributable for the year to ordinary equity holders of the parent by the weighted average number of ordinary shares outstanding during the year. As the net amount attributable for the year to ordinary equity holders of the parent was a loss in the year (2018: loss), the dilutive potential shares are anti-dilutive for the earnings per share calculation. December 31, 2017 2018 201 9 Loss £’000 Weighted shares number Loss per share £ Loss £’000 Weighted shares number Loss per share £ Loss £’000 Weighted shares number Loss per share £ Basic and diluted (38,799 ) 69,012,348 (0.56 ) (32,029 ) 71,144,786 (0.45 ) (34,844 ) 89,424,476 (0.39 ) The Company operates share option schemes (see Note 26) which could potentially dilute basic earnings per share in the future. In addition, there exist within equity nil (2018: 864,988) shares to be issued which also have the potential to dilute basic earnings per share in the future (see Note 18). As part of a license and option agreement with AstraZeneca (see Note 26) additional future payments of a maximum of 1,349,692 new ordinary shares would be payable on reaching certain clinical milestones. Warrants totaling 321,444 were issued in 2019 (2018: 41,286 ) that could potentially dilute basic earnings per share if converted. The equity-settled transactions were considered to be anti-dilutive as they would have decreased the loss per share and were therefore excluded from the calculation of diluted loss per share. For transactions involving ordinary shares or potential ordinary shares between the reporting date and the date of authorization of these financial statements, see Note 30.

Property, plant and equipment

Property, plant and equipment	12 Months Ended
	Dec. 31, 2019
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Property, plant and equipment	12. Property, plant and equipment The Group has decided to present right-of-use On initial application of IFRS 16 (Leases), the Group recognized a right-of-use right-of-use Further details on the initial application of IFRS 16 (Leases) are presented in Note 4. Right-of-use (building) Right-of-use Leasehold improvements Office equipment IT equipment Total Cost or valuation At January 1, 2019 — — 164 31 71 266 Additions — — — — 21 21 Transition to IFRS 16 (Leases) 1,237 1,314 — — — 2,551 Acquisition of subsidiary (Note 5) 10,755 — — 58 24 10,837 Disposals — — — (18 ) — (18 ) Adjustment to carrying value — (290 ) — — — (290 ) Currency translation effects (115 ) — — — — (115 ) At December 31, 2019 11,877 1,024 164 71 116 13,252 Depreciation and impairment At January 1, 2019 — — (53 ) (16 ) (48 ) (117 ) Disposals — — — — — — Depreciation for the year (996 ) (509 ) (16 ) (14 ) (42 ) (1,577 ) At December 31, 2019 (996 ) (509 ) (69 ) (30 ) (90 ) (1,694 ) Net book value At January 1, 2019 — — 111 15 23 149 At December 31, 2019 10,881 515 95 41 26 11,558 Leasehold improvements Office equipment IT equipment Total Cost or valuation At January 1, 2018 155 30 48 233 Additions 9 1 25 35 Disposals — — (2 ) (2 ) At December 31, 2018 164 31 71 266 Depreciation and impairment At January 1, 2018 (37 ) (10 ) (33 ) (80 ) Disposals — — 2 2 Depreciation for the year (16 ) (6 ) (17 ) (39 ) At December 31, 2018 (53 ) (16 ) (48 ) (117 ) Net book value At January 1, 2018 118 20 15 153 At December 31, 2018 111 15 23 149 Leasehold improvements Office equipment IT equipment Total Cost or valuation At January 1, 2017 155 20 43 218 Additions — 10 5 15 Disposals — — — — At December 31, 2017 155 30 48 233 Depreciation and impairment At January 1, 2017 (21 ) (5 ) (18 ) (44 ) Disposals — — — — Depreciation for the year (16 ) (5 ) (15 ) (36 ) At December 31, 2017 (37 ) (10 ) (33 ) (80 ) Net book value At January 1, 2017 134 15 25 174 At December 31, 2017 118 20 15 153

Intangible assets

Intangible assets	12 Months Ended
	Dec. 31, 2019
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Intangible assets	13. Intangible assets Acquired development programs Cost at January 1, 2018 33,005 Cost at December 31, 2018 33,005 Acquisition of subsidiary (Note 5) 12,693 Currency translation effects (171 ) Cost at December 31, 2019 45,527 Revision to estimated value at January 1, 2018 — Revisions to estimated value (373 ) Revision to estimated value at December 31, 2018 (373 ) Revision to estimated value (698 ) Revision to estimated value at December 31, 2019 (1,071 ) Net book value at January 1, 2018 33,005 Net book value at December 31, 2018 32,632 Net book value at December 31, 2019 44,456 The Group’s strategy is to acquire and develop clinical-stage development programs for the treatment of non-rare On April 23, 2019, the Group acquired an intangible asset of £12.7 million following the acquisition of OncoMed (Note 5). On October 28, 2017, the Group acquired the exclusive license for MPH-966 MPH-966 re-measured Acquired development programs Cost at January 1, 2017 25,813 Cost at December 31, 2017 33,005 Cost at December 31, 2018 33,005 Revision to estimate value at January 1, 2017 — Revisions to estimated value — Revision to estimated value at December 31, 2017 — Revision to estimated value (373 ) Revision to estimate value at December 31, 2018 (373 ) Net book value at January 1, 2017 25,813 Net book value at December 31, 2017 33,005 Net book value at December 31, 2018 32,632

Impairment testing of acquired

Impairment testing of acquired development programs not yet available for use	12 Months Ended
	Dec. 31, 2019
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Impairment testing of acquired development programs not yet available for use	14. Impairment testing of acquired development programs not yet available for use Acquired development programs not yet available for use are assessed annually for impairment. The carrying amount of acquired development programs is as follows: As at December 31, 2019 Navicixizumab BPS-804 MPH-966 BGS-649 BCT-197 Total Acquired development programs 12,522 11,616 6,121 9,886 4,311 44,456 As at December 31, 2018 BPS-804 MPH-966 BGS-649 BCT-197 Total Acquired development programs 11,616 6,819 9,886 4,311 32,632 The Group considers the future development costs, the probability of successfully progressing each program to product approval and the likely commercial returns after product approval, among other factors, when reviewing for indicators of impairment. The results of this testing did not indicate any impairment of the acquired products’ rights in the year to December 31, 2019. Management believe that the likelihood of a materially different outcome using different assumptions is remote. The acquired development programs are assets which are not used in launched products. These assets have not yet begun to be amortized but have been tested for impairment by assessing their value in use. Value in use calculations for each program are utilized to calculate the recoverable amount. The calculations use pre-tax out-licensed out-licensing. Key assumptions for the value in use calculations are described as follows: • Development costs to obtain regulatory approval – costs are estimated net of any contributions expected from collaborative arrangements with future partners. Management have developed cost estimates based on their previous experience and in conjunction with the expertise of their clinical development partners; • Launch dates of products – these reflect management’s expected date of launch for products based on the timeline of development programs required to obtain regulatory approval. The assumptions are based on management’s and clinical development partners’ prior experience; • Probability of successful development – management estimates probabilities of success for each phase of development based on industry averages and knowledge of specific programs; • Out-licensing • Sales projections – these are based on management’s internal projections using external market data and market research commissioned by the Company; • Profit margins and other operational expenses – these are based on the Company’s internal projections of current product manufacturing costings, with input from manufacturing partners where applicable, and estimates of operating costs based on management’s prior industry experience; • Cash flow projections – for all assets, cash flows are assessed over an industry-standard asset life of 20 years; and • Discount rates – the discount rate is estimated on a pre-tax Where an out-licensing At this stage of product development, the key sensitivity for all development programs is the probability of successful completion of clinical trials in order to obtain regulatory approval for sale. Therefore, full impairment of a development program is expected should such related trials be unsuccessful.

Other receivables

Other receivables	12 Months Ended
	Dec. 31, 2019
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Other receivables	15. Other receivables December 31, 2018 2019 Rent deposit 293 293 VAT recoverable 316 269 Other receivables — 10 609 572

Cash and short-term deposits

Cash and short-term deposits	12 Months Ended
	Dec. 31, 2019
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Cash and short-term deposits	16. Cash and short-term deposits December 31, 2018 2019 Cash at banks and on hand 5,344 15,803 Short-term deposits 19,698 544 25,042 16,347 Cash at banks earns interest at floating rates based on daily bank deposit rates, with maturity of three months or less. Short-term deposits are available immediately and earn fixed interest at the respective short-term deposit rates and are held in a diversified portfolio of counterparties.

Short-term investments

Short-term investments	12 Months Ended
	Dec. 31, 2019
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Short-term investments	17. Short-term investments December 31, 2018 2019 Short-term investments 2,500 — Short-term investments consist of cash deposits held with greater than three months term to maturity. None of these investments are held with terms greater than a year.

Issued capital and reserves

Issued capital and reserves	12 Months Ended
	Dec. 31, 2019
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Issued capital and reserves	18. Issued capital and reserves Ordinary share capital 2017 Balance at beginning of year 193 Issuances in the year 20 Nominal share capital as at December 31 213 Ordinary shares issued and fully paid Issued on April 3, 2017 for private placement financing round 5,042,017 Issued on April 26, 2017 for conversion of loan note 1,221,361 Issued on October 28, 2017 for acquisition of license 490,798 At December 31, 2017 71,094,974 Nominal value at December 31, 2017 (£) 0.003 Issued capital at December 31, 2017 (£) 213,285 Ordinary share capital 2018 Balance at beginning of year 213 Issuances in the year 1 Nominal share capital as at December 31 214 Ordinary shares issued and fully paid At January 1, 2018 71,094,974 Issued on June 1, 2018 for public offering 50,076 Issued on August 3, 2018 for exercise of share options 10,000 Issued on October 22, 2018 for exercise of share options 85,222 At December 31, 2018 71,240,272 Nominal value at December 31, 2018 (£) 0.003 Issued capital at December 31, 2018 (£) 213,721 Ordinary share capital 2019 Balance at beginning of year 214 Issuances in the year 80 Nominal share capital as at December 31 294 Ordinary shares issued and fully paid At January 1, 2019 71,240,272 Issued on April 23, 2019 for OncoMed acquisition 24,783,320 Issued on June 21, 2019 for conversion of loan note 1,936,030 At December 31, 2019 97,959,622 Nominal value at December 31, 2019 (£) 0.003 Issued capital at December 31, 2019 (£) 293,879 Since January 1, 2017, the following alterations to the Company’s share capital have been made: • Under the private placement dated April 3, 2017, the Company issued and allotted 5,042,017 ordinary shares of £0.003 in nominal value in the capital of the Company on April 3, 2017 at a price of £2.975 per share to institutional investors. Gross cash received was £15,000,000; • On April 26, 2017 Novartis converted £1,398,552 of loan notes dated June 3, 2016 into 632,829 ordinary shares of £0.003 in nominal value in the capital of the Company at the fixed conversion price of £2.21 per share. Under the terms of the notes, Novartis also received 588,532 bonus shares; • On October 31, 2017, Mereo BioPharma Group plc issued 490,798 ordinary shares of £0.003 in nominal value in the capital of the Company to AstraZeneca AB as part payment for the acquisition by Mereo BioPharma 4 Limited of an exclusive license and option to acquire certain assets; • Under the public offering dated June 1, 2018, the Company issued and allotted 50,076 ordinary shares of £0.003 in nominal value in the capital of the Company on June 1, 2018 at a price of £3.00 per share to investors. Gross cash received was £150,228; • On August 3, 2018 the Company issued and allotted 10,000 ordinary shares of £0.003 in nominal value in the capital of the Company pursuant to an exercise of employee share options; • On October 22, 2018 the Company issued and allotted 85,222 ordinary shares of £0.003 in nominal value in the capital of the Company pursuant to an exercise of employee share options; • On April 23, 2019, the Company issued and allotted 24,783,320 ordinary shares of £0.003 in nominal value in the capital of the Company as consideration for the acquisition of OncoMed. The fair value of the ordinary shares, measured on the date of acquisition, was £1.65; and • On June 21, 2019, Novartis converted £2.4 million of loan notes dated June 3, 2016 into 1,071,042 ordinary shares of £0.003 in nominal value in the capital of the Company at a fixed conversion price of £2.21 per share. Under the terms of the notes, Novartis also received 864,988 bonus shares. December 31, Share premium 2017 At January 1, 2017 99,975 Issued on April 3, 2017 for private placement financing round 14,985 Issued on April 26, 2017 for conversion of loan note 2,478 Issued on October 28, 2017 for acquisition of license 1,519 Transaction costs for issued share capital (730 ) At December 31, 2017 118,227 December 31, Share premium 2018 At January 1, 2018 118,227 Issued on June 1, 2018 for public offering 150 Issued on August 3, 2018 for exercise of share options 13 Issued on October 22, 2018 for exercise of share options 110 Transaction costs for issued share capital (8 ) At December 31, 2018 118,492 December 31, Share premium 2019 At January 1, 2019 118,492 Issued on June 21, 2019 for conversion of loan note 3,953 Transaction costs for issued share capital (761 ) At December 31, 201 9 121,684 Other capital reserves Shares to be issued Share-based payments Equity component of convertible loan Total At January 1, 2017 2,673 9,476 517 12,666 Share-based payments expense during the year — 4,983 — 4,983 Shares issued (1,083 ) — — (1,083 ) Equity component of convertible loan instrument — — (207 ) (207 ) At December 31, 2017 1,590 14,459 310 16,359 Shares to be issued Share-based payments Equity component of convertible loan Warrants issued Total At January 1, 2018 1,590 14,459 310 — 16,359 Share-based payments expense during the year — 2,302 — — 2,302 Share-based payments release for exercise of options — (112 ) — — (112 ) Warrants issued for TAP funding — — — 44 44 At December 31, 2018 1,590 16,649 310 44 18,593 Shares to be issued Share-based payments Equity component of convertible Warrants issued for TAP funding Merger Total At January 1, 2019 1,590 16,649 310 44 — 18,593 Acquisition of OncoMed (Note 5) — — — — 40,818 40,818 Shares issued during the year (1,590 ) — — — — (1,590 ) Convertible loan conversion — — (310 ) — — (310 ) Share-based payments expense during the year — 1,636 — — — 1,636 Share-based payments release for exercise of options — — — — — — At December 31, 2019 — 18,285 — 44 40,818 59,147 Share-based payments The Group has various share option schemes under which options to subscribe for the Group’s shares have been granted to certain executives, NEDs and employees. The share-based payment reserve is used to recognize a) the value of equity settled share-based payments provided to employees, including key management personnel, as part of their remuneration and b) deferred equity consideration. Refer to Note 26 for further details. Shares issued or to be issued At January 1, 2019, a maximum of 864,988 shares were remaining to be issued to Novartis pro rata to their percentage shareholding as and when the Company issued further ordinary shares. The fair value of these shares was £1.84 per share. On June 21, 2019, the remaining 864,988 shares were issued to Novartis as fully paid up bonus shares for £nil consideration. Equity component of convertible loan instrument The convertible loan notes issued to Novartis were a compound instrument consisting of a liability and an equity component. On June 21, 2019, Novartis exercised the right to convert the instrument therefore the value of the equity component as at December 31, 2019 is £nil. Merger reserve The consideration paid to acquire OncoMed was 24,783,320 ordinary shares with an acquisition date fair value of £40.9 million, based on the Group’s quoted share price. The nominal value of the issued capital was £0.1 million with the excess, £40.8 million, classified within other capital reserves as a ‘Merger reserve’. Warrants issued for TAP funding The funding arrangements with The Alpha-1 Project 9 8 ) . Accumulated loss Year ended December 31 2017 2018 2019 Other reserves 7,000 7,000 7,000 Accumulated losses (79,316 ) (111,221 ) (146,283 ) Accumulated deficit (72,316 ) (104,221 ) (139,283 ) On March 21, 2016, the Directors of the Company signed a solvency statement with the agreement of all shareholders and undertook a capital reduction, reducing the share premium account by £7.0 million and crediting a new other reserve by the same amount.

Interest-bearing loans and borr

Interest-bearing loans and borrowings	12 Months Ended
	Dec. 31, 2019
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Interest-bearing loans and borrowings	19. Interest-bearing loans and borrowings Year ended December 31 2018 2019 Convertible loan notes (“Novartis Notes”) 2,039 — Bank loan 19,446 20,512 At December 31 21,485 20,512 Current 6,838 15,139 Non-current 14,647 5,373 19.1 Convertible loan notes (“Novartis Notes”) On June 21, 2019, Novartis converted the remaining balance of principal and interest of £2.4 million of convertible loan notes into 1,071,042 ordinary shares at a fixed conversion price of £2.21 per share. This has been recorded as a reduction in interest bearing loans and borrowings of £2.0 million and a reduction in other capital reserves of £0.3 million. Under the terms of the arrangement, Novartis also received 864,988 bonus shares (for full consideration). There are no convertible loan notes outstanding as at December 31, 2019. As at December 31, 2018, the carrying value of the convertible loan notes was £2.0 million. The value of the debt component of the convertible loan notes on the date of issuance of the instrument was £2.9 million. Cash flows attached to the convertible loan note up to the date of maturity were calculated and discounted at an appropriate venture debt rate of 10%. The value of the equity component of the instrument as at December 31, 2018 was £0.3 million. 19.2 Bank loan The bank loan has a principal amount of £20.5 million and will mature on March 1, 2021, unless extended on reaching certain milestones. The terms of the bank loan required interest-only payments up until April 30, 2019, and thereafter payments of interest and principle in 23 equal monthly instalments through maturity. The bank loan bears interest at an annual fixed rate of 8.5% and is secured by substantially all of the Group’s assets, including intellectual property rights owned or controlled by the Group. On April 23, 2019, the Group agreed an amendment to the terms of its bank loan with its lenders. The new terms extended the interest-only period through to December 31, 2019 followed by a 15-month Management estimated the revised carrying value of the loan on May 1, 2019 to be £19.9 million by discounting the revised cash flows at the original discount rate of 18%. The difference between the previous and revised carrying value of the loan on May 1, 2019 was £0.5 million. The gain as a result of the changes in estimated cash flows is recognized as a true-up re-estimation, On May 3, 2019, under the terms of the loan agreement, the Company issued 321,444 additional warrants (Note 21) to its lenders giving them the right to subscribe for ordinary shares at an exercise price of £2.95. The fair value of the additional warrants on their grant date was £0.1 million. A total of £1.5 million (2018: £0.8 million) of non-cash The fair value of the bank loan is not materially different from the carrying amount, since the interest payable on the borrowings is reflective of market rates following the most recent amendment to the bank loan on May 1, 2019. In the prior year, the bank loan was modified and a modification loss of £0.7 million was recognized on the consolidated statement of comprehensive loss on the date of modification. This balance has been reclassified from administrative expenses to finance charges within the statement of comprehensive loss.

Provisions

Provisions	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Provisions	20. Provisions Year ended December 31 2018 2019 Social security contributions on share options 842 104 Provision for deferred cash consideration 2,131 1,654 At December 31 2,973 1,758 Current 332 309 Non-current 2,641 1,449 Year ended December 31 Social security contributions on share options 2017 2018 2019 At beginning of year 1,172 2,288 842 Arising during the year 1,116 — — Released — (1,446 ) (738 ) At December 31 2,288 842 104 Current — — — Non-current 2,288 842 104 The provision for social security contributions on share options is calculated based on the number of options outstanding at the reporting date that are expected to be exercised. The provision is based on the estimated taxable gain arising on exercise of the share options, using the best estimate of the market price at the balance sheet date. Management assume the options will be held for their full contractual life of ten years (see Note 26) therefore the provision has been classified as non-current. The provision has been discounted. The negative charge in 2019 is due to the fall in the Company’s share price between December 31, 2018 and December 31, 2019. Year ended December 31 Provisions for deferred cash consideration 2017 2018 2019 At beginning of year — 2,061 2,131 Arising during the year 2,061 — — Increase in provision due to the unwinding of the time value of money — 443 221 Decrease in provision due to a change in estimates relating to timelines and probabilities of contractual milestones being achieved (see Note 12) — (373 ) (698 ) At December 31 2,061 2,131 1,654 Current 274 332 309 Non-current 1,787 1,799 1,345 The deferred cash consideration is the estimate of the quantifiable but not certain future cash payment obligations due to AstraZeneca for the acquisition of certain assets (see Note 13). This liability is calculated as the risk-adjusted net present value of future cash payments to be made by the Group. The payments are dependent on reaching certain milestones based on the commencement and outcome of clinical trials. The likelihood of achieving such milestones is reviewed at the balance sheet date and increased or decreased as appropriate.

Warrant liability

Warrant liability	12 Months Ended
	Dec. 31, 2019
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Warrant liability	21. Warrant liability Year ended December 31 2017 2018 2019 At beginning of year — 1,346 1,006 Issued during the year 1,292 376 131 Movement during the year 54 (716 ) (1,006 ) At December 31 1,346 1,006 131 At December 31, 2018, as part of the bank loan facility, the Company had issued 922,464 warrants (Note 19) to its lenders giving them the right to subscribe for ordinary shares at a range of exercise price between £2.31 and £3.30. On May 3, 2019, the Company issued a further 321,444 warrants to its lenders giving them the right to subscribe for ordinary shares at an exercise price of £2.95. The fair value of the additional warrants on their grant date was £0.1 million. At December 31, 2019, a total of 1,243,908 warrants are outstanding which are held by lenders of the bank loan facility. The warrants outstanding are equivalent to 1.27% of the ordinary share capital of the Company. The movement during the year ended December 31, 2019 of £1.0 million was mostly due to the decrease in the market price of ordinary shares (refer to table below). The warrant instrument is classified as a financial liability as the terms of the instrument allow for a cashless exercise. At each balance sheet date, the fair value of the warrants will be assessed using the Black Scholes model considering appropriate amendments to inputs in respect of volatility and remaining expected life of the warrants. The following table lists the weighted average inputs to the models used for the fair value of warrants granted during the year ended December 31: Year ended December 31 2018 2019 Expected volatility (%) 65 67 Risk-free interest rate (%) 1.56 1.26 Expected life of share options (years) 10 10.0 Market price of ordinary shares (£) 2.31 0.83 Model used Black Scholes Black Scholes Since there is no historical data in relation to the expected life of the warrants, the contractual life of the options was used in calculating the expense for the year. Volatility was estimated by reference to the share price volatility of a group of comparable companies over a retrospective year equal to the expected life of the warrants.

Other liability

Other liability	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Other liability	22. Other liability Year ended December 31 2018 2019 At beginning of year — 34 Interest accretion — 10 Arising during the year 34 — At December 31 34 44 On October 8, 2018, the Group entered into a funding agreement with The Alpha-1 MPH-966 8 MPH-966. The first payment (“Payment 1”) of $100,000 (£78,445) was made to Mereo on November 16, 2018. The fair value of the liability of Payment 1 on November 16, 2018 was £34,289. Application of the effective interest method is required to accrete the initial liability value up to the face value of the liability over a period of five years, being the estimate of the earliest date that the liability could be repaid and assuming that the agreement is not terminated earlier. This non-cash The fair value of warrants issued as part of Payment 1 on November 16, 2018 was £44,156.

Trade and other payables

Trade and other payables	12 Months Ended
	Dec. 31, 2019
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Trade and other payables	23. Trade and other payables Year ended December 31 2018 2019 Trade payables 4,393 6,148 Social security and other taxes 161 183 Other payables 16 21 At December 31 4,570 6,352 Terms and conditions of the above financial liabilities: • Trade payables are non-interest 30-day • Other payables are non-interest

Changes in liabilities arising

Changes in liabilities arising from financing activities	12 Months Ended
	Dec. 31, 2019
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Changes in liabilities arising from financing activities	24. Changes in liabilities arising from financing activities Contingent Lease Bank Novartis Warrant Deferred cash consideration TAP Total Carrying value at January 1, 2018 — — 18,775 1,977 1,346 2,061 — 24,159 Financing cash flows — — (2,111 ) — — — 34 (2,077 ) Changes in fair values — — (375 ) — (716 ) 70 — (1,021 ) Interest expense — — 2,427 185 — — — 2,612 Loss on modification — — 730 — — — — 730 Other — — — (124 ) 375 — — 251 Carrying value December 31, 2018 — — 19,446 2,038 1,005 2,131 34 24,654 Adoption of IFRS 16 (Leases) — 2,534 — — — — — 2,534 Financing cash flows — (2,212 ) (1,739 ) — — — — (3,951 ) Changes in foreign exchange — (131 ) — — — — — (131 ) Changes in fair values 354 — — — (874 ) (477 ) 10 (987 ) Interest expense — 1,314 3,262 20 — — — 4,596 Gain on modification — — (457 ) — — — — (457 ) Issuance of equity — — — (2,058 ) — — — (2,058 ) Acquisition of subsidiary (Note 5) — 10,689 — — — — — 10,689 Lease term reassessment — (290 ) — — — — — (290 ) Carrying value at December 31, 2019 354 11,904 20,512 — 131 1,654 44 34,599

Financial and capital risk mana

Financial and capital risk management and fair value measurement	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Financial and capital risk management and fair value measurement	25. Financial and capital risk management and fair value measurement 25.1 Capital risk management For the purpose of the Group’s capital management, capital includes issued capital, share premium, the equity component of a convertible loan note and all other equity reserves attributable to the equity holders of the parent. The Group’s objectives when managing capital are to safeguard the ability to continue as a going concern and ensure that sufficient capital is in place to fund the Group’s R&D activities. The Group’s principal method of adjusting the capital available is through issuing new shares or arranging suitable debt financing, including any related warrants. The Group’s share capital and share premium are disclosed in Note 18. The Group’s loans are disclosed in Note 19. The Group monitors the availability of capital with regard to its committed and planned forecast future expenditure on an ongoing basis. The Group has set up an Employee Benefit Trust which makes market purchases of the Company’s shares to provide some cover against future exercise of options under the Company’s share option schemes (see Note 28). 25.2 Financial risk management objectives and policies Monitoring of financial risk is part of the Board’s ongoing risk management, the effectiveness of which is reviewed annually. Our agreed policies are implemented by the Chief Financial Officer, who submits periodic reports to the Board. The Group seeks to maintain a balance between equity capital and convertible and secured debt to provide sufficient cash resources to execute the business plan. In addition, the Group maintains a balance between cash held on deposit and short-term investments in Sterling and other currencies to reduce its exposure to foreign exchange fluctuations in respect of its planned expenditure. Except for the bank loan, the Group’s principal financial instruments comprise trade payables which arise directly from its operations and are not designed as a means of raising finance for the Group’s operations. The Group has various financial assets, such as receivables and cash and short-term deposits. The Group does not consider that its financial instruments gave rise to any material financial risks during the year to December 31, 2019. Interest rate risk The Group’s policy in relation to interest rate risk is to monitor short and medium-term interest rates and to place cash on deposit for periods that optimize the amount of interest earned while maintaining access to sufficient funds to meet day-to-day The interest payable on the bank loan is fixed. Consequently, there is no material exposure to interest rate risk in respect of interest payable. Foreign currency risk The Group currently has no revenue. The majority of operating costs are denominated in pound sterling, Euros and U.S. Dollars. Funding to date has been secured in a mixture of pound sterling and U.S. Dollars and therefore a level of natural hedging exists in respect of operating costs. Foreign exchange risk arises from commercial transactions and recognized assets and liabilities in foreign currencies. Credit risks The Group’s policy is to place funds with financial institutions which have a minimum long-term credit rating with Standard & Poor’s of A. The Group also allocates a quota to individual institutions in respect of cash deposits and also seeks to diversify its investments where this is consistent with achieving competitive rates of return. It is the Group’s policy to place not more than £10 million with any one investment counterparty and no more than £5 million with any one cash deposit counterparty. Cash flow and liquidity risk Credit risk from balances with banks and financial institutions is managed by the Group’s finance department in accordance with the Group’s policy. Investments of surplus funds are made only with approved counterparties and within credit limits assigned to each counterparty. Counterparty credit limits are reviewed by the Group’s Board of Directors on an annual basis and may be updated throughout the year subject to approval of the Group’s Audit and Risk Committee. The limits are set to minimize the concentration of risks and therefore mitigate financial loss through a counterparty’s potential failure to make payments. The Group’s maximum exposure to credit risk for the components of the balance sheet at December 31, 2019 is the carrying amounts. The Group does not face a significant liquidity risk with regards to its lease liabilities. The Group monitors its funding requirements through preparation of short-term, mid-term 25.3 Fair value hierarchy Fair value measurement using Date of valuation Total Quoted prices in active markets (Level 1) Significant observable inputs (Level 2) Significant unobservable inputs (Level 3) Liabilities measured at fair value Provision for deferred cash consideration (Note 20) December 31, 2019 1,654 — — 1,654 Provision for contingent consideration (Note 5) December 31, 2019 354 — — 354 Warrant liability (Note 21) December 31, 2019 131 — 131 — Liabilities for which fair values are disclosed Bank loan (Note 19) December 31, 2019 20,512 — 20,512 — There were no transfers between Level 1 and Level 2 during 2019. Fair value measurement hierarchy for liabilities as at December 31, 2018: Fair value measurement using Date of valuation Total Quoted prices in active markets (Level 1) Significant observable inputs (Level 2) Significant unobservable inputs (Level 3) Liabilities measured at fair value Provision for deferred cash consideration (Note 20) December 31, 2018 2,061 — — 2,061 Warrant liability (Note 21) December 31, 2018 1,346 — 1,346 — Liabilities for which fair values are disclosed Convertible loan (Note 19) December 31, 2018 1,977 — 1,977 — Bank loan (Note 19) December 31, 2018 18,775 — 18,775 — There were no transfers between Level 1 and Level 2 during 2018. The management of the Group assessed that the fair values of cash and short-term deposits, other receivables, trade payables, and other current liabilities approximate their carrying amounts largely due to the short-term maturities of these instruments. The following table presents the changes in level 3 items for the periods ended December 31, 2019 and December 31, 2018: Provision for Provision for January 1, 2018 2,061 — Unwinding of the time value of money recognised as a finance charge 443 — Change in estimate relating to probabilities (revision to intangible asset, see Note 13) (373 ) — December 31, 2018 2,131 — January 1, 2019 2,131 — Unwinding of the time value of money (recognized as a finance charge) 221 — Change in estimate relating to probabilities (revision to intangible asset, see Note 13) (698 ) — Change in estimate relating to probabilities (recognized as an administrative expense) — 354 December 31, 2019 1,654 354 The following methods and assumptions were used to estimate the fair values: • The warrant liability is estimated using a Black Scholes model, taking into account appropriate amendments to inputs in respect of volatility, remaining expected life of the warrants, cost of capital, probability of success and rates of interest at each reporting date. • The fair value of the provision for deferred cash consideration is estimated by discounting future cash flows using rates currently available for debt on similar terms and credit risk. In addition to being sensitive to a reasonably possible change in the forecast cash flows or the discount rate, the fair value of the deferred cash consideration is also sensitive to a reasonably possible change in the probability of reaching certain milestones. The valuation requires management to use unobservable inputs in the model, of which the significant unobservable inputs are disclosed in the tables below. Management regularly assesses a range of reasonably possible alternatives for those significant unobservable inputs and determines their impact on the total fair value. • At December 31, 2019, the Group estimates the fair value of the contingent consideration liability to be £0.4 million, which is an increase from £nil on the date of acquisition. Total potential payments under the CVR arrangement on a gross, undiscounted basis are approximately $80.0 million (see Note 13). The increase in the fair value of the contingent consideration liability reflects the terms subsequently agreed with Oncologie, Inc. (“Oncologie) with respect to the global licensing agreement of navicixizumab (“Navi”) (see Note 30). The estimated contingent consideration payable is based on a risk-adjusted, probability-based scenario. Under this approach the likelihood of future payments being made to the former shareholder of OncoMed under the CVR arrangement is considered. The estimate could materially change over time as the development plan and subsequent commercialization of the Navi product progresses. The significant unobservable inputs used in the fair value measurements categorized within Level 3 of the fair value hierarchy, together with a quantitative sensitivity analysis as at December 31, 2019 and 2018 are as shown below: Valuation Significant unobservable inputs Input r ( average ) Sensitivity of the input to fair value Provision for deferred cash consideration DCF WACC 2019: 15.3% 1% increase would result in a decrease in fair value by £38,000 . WACC 2018: 15.3% 1% decrease would result in an Probability of success 2019: 15.8–95% 10% increase would result in an Probability of success 2018: 28%–95% 10% decrease Contingent consideration liability DCF Ongoing uncertainty in the clinical development of the Navi product. Not applicable Total potential payments future payments relating to the contingent consideration liability on a gross, undiscounted basis are approximately $80.0 million (see Note 30). Regulatory approval and commercialisation risks. Sensitivity of the input to fair value is primarily driven by uncertainty in the clinical development of the Navi product. As at December 31, 2019, we are completing a Phase 1b clinical trial. Future potential payments under the CVR arrangement are contingent on i) future development milestones and ii) future sales of the Navi product, following regulatory approval and commercialisation. 25.4 Financial assets at fair value through other comprehensive income During the year, the Group acquired £29.0 million of short-term debt investments following the acquisition of OncoMed (Note 5). The short-term debt investments acquired were in U.S. Treasury Bills (“T-Bill”) All the short-term debt investments have reached maturity and been sold during the year, therefore the carrying value as at December 31, 2019 is £nil. On maturity, the related balance held within other comprehensive income has been reclassified to finance income within the consolidated statement of comprehensive loss. 25.5 Liquidity risk The table below summarizes the maturity profile of the Group’s financial liabilities based on contractual undiscounted payments at December 31, 2019: Payments due by period Up to 1 year 1–3 years 3–5 years Over 5 years Total Bank loan (Note 19) 17,185 5,484 — — 22,669 Leases (Note 4) 2,634 4,643 4,913 8,105 20,295 Trade and other payables (Note 23) 6,352 — — — 6,352 Contingent consideration liability (Note 5) 354 — — — 354 26,525 10,127 4,913 8,105 49,670 Further details regarding the contingent consideration liability following the acquisition of OncoMed are provided in Note 5. The table below summarizes the maturity profile of the Group’s financial liabilities based on contractual undiscounted payments at December 31, 2018: Payments due by period Up to 1 year 1–3 years 3–5 years Over 5 years Total Convertible loan (Note 19) 83 2,162 — — 2,245 Bank loan (Note 19) 8,260 15,589 — — 23,849 Leases (Note 27) 332 204 — — 536 Trade and other payables (Note 23) 4,570 — — — 4,570 13,245 17,955 — — 31,200 The Group may incur potential payments upon achievement of clinical, regulatory and commercial milestones, as applicable, or royalty payments that may be required to be made under license agreements the Group entered into with various entities pursuant to which the Group has in-licensed 25.6 Market risk The functional currency of the Company and all subsidiaries is pound sterling except for OncoMed whose functional currency is US dollars. The Group incurs expenditures in foreign currencies and is exposed to the risks of foreign exchange rate movements, with the impact recognized in the consolidated statement of comprehensive loss. The Group seeks to minimize this exposure by passively maintain foreign currency cash balances at levels appropriate to meet foreseeable foreign currency expenditures. The table below shows analysis of the pound sterling equivalent of period-end Year ended Year ended Cash at bank and in hand: Pound sterling 2,525 23,189 US dollars 13,807 1,809 Swiss francs 11 — Euro 4 44 16,347 25,042 The table below shows those transactional exposures that give rise to net currency gains and losses recognized in the consolidated income statement. Such exposures comprise the net monetary assets and monetary liabilities of the Group that are not denominated in the functional currency of the relevant Group entity. As at year end, these exposures were as follows: Year ended Year ended Net foreign currency assets / (liabilities): US dollars (219 ) (542 ) Swiss francs (6 ) — Euro (812 ) (1,430 ) (1,037 ) (1,972 ) The most significant currencies in which the Group transacts, other than pound sterling, are the US dollar and the Euro. The Group also trades in other currencies in small amounts as necessary. The following table details the Group’s sensitivity to a 10% change in the period-end Year ended December 31, 2019 US dollar Euro Net foreign currency assets / (liabilities): Loss before tax 20 74 Equity 20 74 Year ended December 31, 2018 US dollar Euro Net foreign currency assets / (liabilities): Loss before tax 49 130 Equity 49 130 In management’s opinion, the sensitivity analysis is unrepresentative of the inherent foreign exchange risk as the period end exposure does not reflect the exposure during the period.

Share-based payments

Share-based payments	12 Months Ended
	Dec. 31, 2019
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Share-based payments	26. Share-based payments The charge for share-based payments under IFRS 2 arises across the following schemes: Year ended December 31, 2017 2018 2019 2019 Equity Incentive Plan — — 635 2019 NED Equity Incentive Plan — — 160 2015 Plan 2,442 806 63 Mereo BioPharma Group plc Share Option Plan 586 1,064 685 Long Term Incentive Plan 299 320 93 Deferred Bonus Share Plan 325 — — 3,652 2,190 1,636 26.1 2019 Equity Incentive Plan (“EIP”) Our Board adopted the 2019 EIP on April 4, 2019. The 2019 EIP provides for the grant of market value options over ADR’s (each ADR represented by 5 ordinary shares) to executive directors and employees. During the year, market value options were granted to executive directors remainder shall vest in equal monthly instalments over the three-year period following the first anniversary. No performance conditions apply to such market The fair value of share options granted was estimated at the date of grant using a Black Scholes pricing model, taking into account the terms and conditions upon which the share options were granted. The fair value calculation does not include any allowance for dividends as the Company has no available profits for distribution. The exercise price of the share options will be equal to the market price of the underlying shares on the date of grant. The contractual term of the share options is 10 years. Movements during the year The following table illustrates the number and weighted average exercise prices (WAEP) of, and movements in, options for the 2019 EIP during the year: 2019 Options Number WAEP $ Outstanding at beginning of the year — — Granted during the year 801,200 4.29 Cancelled during the year 3,150 5.40 Forfeited during the year — — Exercised during the year — — Outstanding at December 31 798,050 4.29 Exercisable at December 31 — — The weighted average remaining contractual life for the share options outstanding as at December 31, 2019 was 9.5 years. The weighted average fair value of options granted during the year was £0.49 (2018: £nil). Options outstanding at the end of the year had an exercise price of between $ $ 26.2 2019 Non-Executive Our Board adopted the 2019 NED EIP on April 4, 2019. The 2019 NED EIP provides for the grant of market value options over ADR’s non-executive S one-year The fair value of share options granted was estimated at the date of grant using a Black Scholes pricing model, taking into account the terms and conditions upon which the share options were granted. The fair value calculation does not include any allowance for dividends as the Company has no available profits for distribution. The exercise price of the share options will be equal to the market price of the underlying shares on the date of grant. The contractual term of the share options is 10 years. Movements during the year The following table illustrates the number and weighted average exercise prices (WAEP) of, and movements in, options for the 2019 NED EIP during the year: 2019 Options Number WAEP $ Outstanding at beginning of the year — — Granted during the year 77,000 4.20 Cancelled during the year — — Forfeited during the year — — Exercised during the year — — Outstanding at December 31 77,000 4.20 Exercisable at December 31 38,472 4.40 The weighted average remaining contractual life for the share options outstanding as at December 31, 2019 was 9.5 years. The weighted average fair value of options granted during the year was £0.49 (2018: £nil). Options outstanding at the end of the year had an exercise price of between $ $ 26.3 The 2015 Plan Under the Mereo BioPharma Group Limited Share Option Plan (the “2015 Plan”), the Group, at its discretion, granted share options to employees, including executive management and NEDs. Share options vest over four years for executive management and employees and over three years for NEDs. No further share option grants are envisaged under the 2015 Plan. Movements during the year The following table illustrates the number and weighted average exercise prices (WAEP) of, and movements in, options for the 2015 Plan during the year: 2017 2018 2019 Number WAEP £ Number WAEP Number WAEP £ Outstanding at beginning of the year 9,198,655 1.32 9,124,610 1.32 8,983,133 1.32 Granted during the year — — — — — — Cancelled during the year — — — — — — Forfeited during the year (74,045 ) 1.29 (46,255 ) 1.29 (59,533 ) 1.29 Exercised during the year — — (95,222 ) 1.29 — — Outstanding at December 31 9,124,610 1.32 8,983,133 1.32 8,923,600 1.32 Exercisable at December 31 5,655,676 1.31 8,007,029 1.31 8,901,478 1.32 The weighted average remaining contractual life for the share options outstanding as at December 31, 2019 was 5.6 years (2018: 6.6 years). Options outstanding at the end of the year had an exercise price of between £1.29 and £2.21. 26.4 The Mereo BioPharma Group plc Share Option Plan The Mereo BioPharma Group plc Share Option Plan (“Share Option Plan”) provides for the grant of options to acquire our ordinary shares to employees, executive directors and executive officers. Options may be granted to all eligible employees on commencement of employment and may be granted on a periodic basis after that. Under the Share Option Plan, our Board of Directors may determine if the vesting of an option will be subject to the satisfaction of a performance condition. Following the introduction of the EIP and NED EIP, no further share option grants under the Share Option Plan are envisaged. Movements during the year The following table illustrates the number and weighted average exercise prices (WAEP) of, and movements in, options for the Option Plan during the year: 2017 2018 2019 Number WAEP £ Number WAEP £ Number WAEP £ Outstanding at beginning of the year — — 1,578,188 3.05 1,881,555 3.10 Granted during the year 1,593,188 3.05 388,000 3.14 — — Cancelled during the year — — — — — — Forfeited during the year (15,000 ) 3.03 (84,633 ) 3.03 (357,490 ) 3.21 Outstanding at December 31 1,578,188 3.05 1,881,555 3.10 1,524,065 3.07 Exercisable at December 31 — — — — 40,141 3.03 The weighted average remaining contractual life for the share options outstanding as at December 31, 2019 was 7.6 years (2018: 8.6 years). The weighted average fair value of options granted during the year was £nil (2018: £2.29). Options outstanding at the end of the year had an exercise price of between £2.76 and £3.25. 26.5 Long Term Incentive Plan Under the Company’s Long Term Incentive Plan (LTIP), initiated in 2016, the Group, at its discretion, may grant nil-cost The fair value of the LTIP Share Price Element is estimated at the date of grant using a Monte Carlo pricing model, taking into account the terms and conditions upon which the share options were granted. The fair value of the LTIP Strategic Element is estimated at the date of grant using a Black Scholes pricing model, taking into account the terms and conditions upon which the share options were granted, and the expense recorded is based upon the expected level of achievement of non-marked With respect to the LTIP Strategic Element, during the year the non-market recognized The fair value calculations do not include any allowance for dividends as the Company has no available profits for distribution. The contractual term of the LTIP options is five years. The expense recognized for employee services received during the year to December 31, 2019 was £0.1 million (2018: £0.3 million). 2017 Number 2018 Number 2019 Number Granted during the year 185,950 — — Cancelled during the year — — — Lapsed during the year — — (241,374 ) Outstanding at December 31 1,151,446 1,151,446 910,072 Exercisable at December 31 — — — During the year 241,373 options under the LTIP Share Price Element lapsed as the performance conditions for a tranche were not met. The weighted average remaining contractual life for the LTIP options outstanding as at December 31, 2019 was 0.9 years (2018: 1.8 years). The weighted average fair value of LTIP options granted during the year to December 31, 2019 was £nil (2018: £nil). The following tables list the weighted average inputs to the models used for the fair value of LTIP options granted during the years ended December 31, 2017, 2018 and 2019. LTIP Share Price Element Year ended December 31 2017 2018 201 9 Expected volatility (%) 51.7 — — Risk-free interest rate (%) 0.17-0.39 — — Expected life of share options (years) 3-5 — — Market price of ordinary shares (£) 3.03 — — Model used Monte Carlo — — LTIP Strategic Element Year ended December 31 2017 2018 201 9 Expected volatility (%) 51.7 — — Risk-free interest rate (%) 0.39 — — Expected life of share options (years) 5 — — Market price of ordinary shares (£) 3.03 — — Model used Black Scholes — — Since there is no historical data in relation to the expected life of the LTIP options, the contractual life of the options has been used in calculating the expense for the year. Volatility is estimated by reference to the share price volatility of a group of comparable companies over a retrospective period equal to the expected life of the LTIP options. 26.6 Deferred Bonus Share Plan Under the previous terms of the Company’s Deferred Bonus Share Plan (DBSP), 30% of the annual bonus for 2017 for the senior management team was payable in deferred shares, which are governed by the DBSP plan rules. At the date of grant of the awards, the monetary bonus amount will be divided by the closing share price to give the number of shares issued to the employee under the DBSP. The number of shares is fixed and not subject to adjustment between the issue date and vesting date. Under the DBSP, awards vest after three years from the date of the award. There are no further performance conditions attached to the award, nor any service conditions (including no requirement for continued employment once the awards have been made). Since the awards are issued at nil cost, they will be satisfied by the issue of shares from the Employee Benefit Trust. The following table illustrates the number of, and movements in, DBSP options during the year: 2017 Number 2018 Number 2019 Number Outstanding at January 1 62,180 163,000 163,000 Awarded during the year 100,820 — — Granted during the year — — — Outstanding at December 31 163,000 163,000 163,000 Exercisable at December 31 — — — The weighted average remaining contractual life for the DBSP options outstanding as at December 31, 2019 was 1.6 years (2018: 2.6 years). The weighted average fair value of DBSP options granted during the year was £nil (2018: £nil). From January 1, 2018, under the new Deferred Bonus Plan (“2019 DBP”), 100% of the annual bonus is paid in cash, of which 30% of amounts granted to Executive Directors (after deduction of income tax and the relevant employee’s national insurance contributions) is required to be utilized to acquire shares in the Company in the open market within 12 months of the grant of the award. No further grants under the DBSP are envisaged. 26.7 Deferred equity consideration In October 2017, our wholly owned subsidiary Mereo BioPharma 4 Limited entered into an exclusive license and option agreement (the “License Agreement”), to obtain from AstraZeneca an exclusive worldwide, sub-licensable MPH-966, Under the agreement with AstraZeneca, the Company may issue up to 1,349,693 ordinary shares which are dependent on achieving certain milestones. In respect of milestones that are probable, the Group has accounted for, but not yet issued, 429,448 ordinary shares which have been measured at fair value on grant date, being £3.10, giving a total of £1.3 million. 26.8 Weighted average inputs The following tables list the weighted average inputs to the models used for the fair value of share options granted during the year ended December 31, 2019: EIP 2019 NED EIP 2019 grants Expected volatility (%) 66 66 Risk-free interest rate (%) 0.95 0.97 Expected life of share options (years) 10 10 Market price of ordinary shares (£) 0.66 0.63 Model used Black Scholes Black Scholes During the year ended December 31, 2019, grants were issued under the EIP 2019 and NED EIP 2019 plans. The following tables list the weighted average inputs to the models used for the fair value of share options granted during the year ended December 31, 2018: Share option plan grants Expected volatility (%) 65 – 67 Risk-free interest rate (%) 1.39 – 1.53 Expected life of share options (years) 10 Market price of ordinary shares (£) 2.76 – 3.25 Model used Black Scholes During the year ended December 31, 2018, grants were issued under the share option plan. Grants issued in previous years under the LTIP Strategic element are subject to fair value movements at each reporting date.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2019
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Commitments and contingencies	27. Commitments and contingencies 27.1 Group as a lessee Following the adoption of IFRS 16 (Leases), information relating to the Group as a lessee can be found in Note 4 (Changes in accounting policies), Note 1 2 27.2 Operating lease arrangements Operating leases, in which the Group is the sublessor, relate to a portion of an office leased by the Group, with lease terms of between one to two years. One of the subleases has an automatic extension on a month-to-month The unguaranteed residual values do not represent a significant risk for the Group, as the lease terms are for a remaining period of 12 months or less, and the Group expects to be able to enter into new leases at market value at the end of the sublease term. The maturity analysis of payments receivable by the Group in its capacity as sublessor is disclosed below: December 31, December 31, Within one year 552 — After one year but not more than five years — — More than five years — — 552 — The Group does not have any leasing arrangements classified as finance leases at December 31, 2019 (2018: £nil). 27.3 Financial commitments Each of Mereo BioPharma 1 Limited, Mereo BioPharma 2 Limited and Mereo BioPharma 3 Limited issued to Novartis loan notes (the “Novartis Notes”) (which were assigned by Novartis to the Company in exchange for ordinary shares pursuant to the Subscription Agreement) and each of Mereo BioPharma 1 Limited, Mereo BioPharma 2 Limited and Mereo BioPharma 3 Limited agreed to make future payments to Novartis comprising amounts equal to ascending specified percentages of tiered annual worldwide net sales (beginning at high single digits and reaching into double digits at higher sales) by such subsidiary of products that include the assets acquired. The levels of ascending percentages of tiered annual worldwide net sales are the same for each of Mereo BioPharma 1 Limited, Mereo BioPharma 2 Limited and Mereo BioPharma 3 Limited under the respective Purchase Agreements. Each of Mereo BioPharma 1 Limited, Mereo BioPharma 2 Limited and Mereo BioPharma 3 Limited further agreed that in the event it transfers, licenses, assigns or leases all or substantially all of its assets, it will pay Novartis a percentage of the proceeds of such transaction. The Company will retain the majority of the proceeds from such a transaction. Such percentage is the same for each of Mereo BioPharma 1 Limited, Mereo BioPharma 2 Limited and Mereo BioPharma 3 Limited under the respective Purchase Agreements. The payment of a percentage of proceeds is not payable with respect to any transaction involving equity interests of Mereo BioPharma Group plc, a merger or consolidation of Mereo BioPharma Group plc, or a sale of any assets of Mereo BioPharma Group plc. In October 2017, the Group’s wholly owned subsidiary Mereo BioPharma 4 Limited entered into an exclusive license and option agreement (“the License Agreement”), to obtain from AstraZeneca an exclusive worldwide, sub-licensable MPH-966, MPH-966. sub-licensing licensed-product-by-licensed-product country-by-country sub-licenses sub-licenses The License Agreement will expire on the expiry of the last-to-expire

Related party disclosures

Related party disclosures	12 Months Ended
	Dec. 31, 2019
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Related party disclosures	28. Related party disclosures 28.1 Compensation of key management personnel of the Group The remuneration of key management personnel of the Group is set out below in aggregate: Year ended December 31, 2017 2018 2019 Short-term benefits 2,757 3,176 3,488 Post-employment benefits 87 60 64 IFRS 2 share-based payment charge 2,726 1,470 1,152 Total compensation paid to key management personnel 5,570 4,706 4,704 The amounts disclosed in the table above are the amounts recognized non-executive 28.2 Employee Benefit Trust In 2016 the Company set up an Employee Benefit Trust (“EBT”) for the purposes of buying and selling shares on the employees’ behalf. A total of £1.0 million of funding was paid into the EBT by the Company during the year ended December 31, 2019 (2018: £0.3 million). A total of 1,074,274 shares were purchased by the EBT during the year ended December 31, 2019 (2018: 163,000). As at December 31, 2019 a cash balance of £21,762 (2018: £21,762) was held by the EBT . 28.3 Novartis Notes On June 6, 2019, Novartis delivered to the Company a notice of conversion with respect to the aggregate principal amount and interest of the Novartis Notes. Pursuant to such notice, on June 21, 2019, £2.4 million aggregate principal amount of Novartis Notes was converted into 1,071,042 fully paid ordinary shares at a fixed conversion price of £2.21 per ordinary share (see Note 18). Additionally, in connection with such conversion, the Company issued 864,966 bonus shares to Novartis. On February 10, 2020, the Company entered into a £3.8 million convertible equity financing with Novartis Pharma (AG) (“Novartis”). Under the terms of the convertible equity financing, Novartis will purchase $5 million in a convertible loan note (see Note 30).

Standards issued but not yet ef

Standards issued but not yet effective	12 Months Ended
	Dec. 31, 2019
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Standards issued but not yet effective	29. Standards issued but not yet effective Certain new accounting standards and interpretations have been published that are not mandatory for December 31, 2019 reporting periods and have not been early adopted by the Group. These standards are not expected to have a material impact on the entity in the current or future reporting periods and on foreseeable future transactions.

Events after the reporting peri

Events after the reporting period	12 Months Ended
	Dec. 31, 2019
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Events after the reporting period	30. Events after the reporting period 30.1 Global licensing agreement On January 13, 2020, the Company and Oncologie, Inc. (“Oncologie”) announced a global licensing agreement for the development and commercialization of navicixizumab (“Navi”). Under the terms of the global licensing agreement, Oncologie will receive an exclusive worldwide license to develop and commercialize Navi. The Company received an upfront payment of $4 million on January 17, 2020 mid-single sub-teen As a consequence of the global licensing agreement with Oncologie, and in accordance with the terms and conditions of the Contingent Value Rights Agreement for former stockholders of OncoMed, dated April 23, 2019, by and among the Company and Computershare Inc., as rights agent, (the “Mereo CVR Agreement”), holders of contingent value rights (“CVRs”) pursuant to the Mereo CVR Agreement will be entitled to receive certain eligible cash milestone payments made to the Company under the global licensing agreement relating to Navi. Those eligible cash milestone payments are equal to 70% of the aggregate principal amount received by the Company after deduction of costs, charged and expenditures within a period of five years following completion of the OncoMed acquisition on April 23, 2019. Such eligible milestone payments are subject to a cash consideration cap of approximately $79.7 million. As at December 31, 2019, the Company was would be made under the Mereo CVR Agreement. The full amount is recorded as a contingent consideration payable on the consolidated balance sheet as at December 31, 2019 and was subsequently paid out in the Q1 2020. 30.2 Novartis convertible equity financing On February 10, 2020, the Company entered into a £ 3.8 million convertible equity financing with Novartis Pharma (AG) (“Novartis”). Under the terms of the convertible equity financing, Novartis will purchase £ 3.8 million in a convertible loan note (“Loan Note”). The Loan Note is convertible at any time at the option of the holder, at a fixed price of £0.265 per ordinary share. The maturity of the Loan Note is three years from issuance, and it bears an interest rate of 6% per annum. In connection with the Loan Note issuance, the Company also issued a warrant instrument to Novartis to purchase up to 1,449,614 of the Company’s ordinary shares, which are exercisable at an exercise price of £0.265 per ordinary share at any time before the close of business on February 10, 2025. 30.3 Aspire Capital Securities Purchase Agreement On February 10, 2020, the Company entered into a Securities Purchase Agreement (the “Agreement”) to issue up to $28 million of the Company’s ordinary shares exchangeable for American Depositary Shares (“ADSs”), including a $3 million initial purchase, with Aspire Capital Fund, LLC (“Aspire Capital”), a Chicago-based institutional investor. Under the terms of the Agreement, Aspire Capital has made an initial investment of $3 million to purchase 11,423,925 of the Company’s ordinary shares (equivalent to 2,286,585 ADSs) at a price equivalent to $1.31 per ADS, which represents a 16% discount over Mereo’s ADS closing stock price of $1.56 on February 8, 2020. Under the terms of the Agreement, Aspire Capital has also committed to subscribe at Mereo’s request from time to time during a 30-month period for up to an additional $25 million of Mereo’s ordinary shares exchangeable for ADSs at prices based on the ADS market price at the time of each sale. In consideration for Aspire Capital’s initial investment and its commitment to purchase up to an additional $25 million ADSs, Mereo has agreed to pay Aspire Capital a commission to be satisfied wholly by the issue to Aspire Capital of a further 2,862,595 of the Company’s ordinary shares (equivalent to 572,519 ADSs). 30.4 Equity investment from Boxer Capital, LLC On February 19, 2020, the Company entered into a Securities Purchase Agreement with Boxer Capital, LLC to 30.5 Share-based payments On February 20, 2020, the Company granted 962,836 market value options over ADSs under the Mereo 2019 EIP (Note 26.1) to certain Executive Directors and other employees at an exercise price of $1.84 per ADS. On the same date, the Company granted 77,000 market value options over ADSs under the Mereo 2019 NED EIP (Note 26.2) to certain Non-Executive Directors at an exercise price of $1.84 per ADS. 30.6 Issuance of additional warrants to lenders Following the transactions noted above, it is anticipated that a further 362,534 additional warrants will be issued to the lenders of the bank loan facility giving them the right to subscribe for ordinary shares at an exercise price of £2.95 (see Note 21). 30.7 Resignation of Chief Financial Officer (“CFO”) On March 27, 2020, we announced the resignation of Richard Jones. Michael Wyzga, a Non-Executive Director, will assume the role of Interim Chief Financial Officer following the departure of Richard Jones. Richard Jones will remain in his position as CFO for a transitionary period of up to five months. For further details, refer to Executive Officer Remuneration within the annual report on Form 20-F. 30.8 Coronavirus (“COVID-19”) Public health epidemics or outbreaks could adversely impact our business. In late 2019, a novel strain of COVID-19, also known as coronavirus, was reported in Wuhan, China. Since, COVID-19 has now spread to several other countries, including the U.K. and U.S., and infections have been reported globally. The extent to which COVID-19 impacts our operations will depend on future developments, which are highly uncertain and cannot be predicted with confidence, including the duration and severity of the outbreak. At the date of this report, the Company continues to monitor the outbreak and impact of COVID-19 and is actively implementing specific precautionary measures to mitigate potential disruptions accordingly. 30.9 Equity Fund Raise On June 3, 2020, Mereo BioPharma Group plc completed a private placement (the “Fundraising”) of $70 million (£56 million) before commission and expenses with a number of new and existing principally U.S based institutional and accredited investors (the “Purchasers”). The net proceeds from the Fundraising will be used primarily to fund clinical development activities of the Company’s lead product candidates and for general corporate purposes. The Company will utilise $13 million (£10.4 million) to reduce current indebtedness (including interest) of $17.6 million (£14.1 million). In the absence of the receipt of any other income, the Board expects that the resulting net proceeds of the Fundraising will fund the Company into early 2022. The Fundraising comprised proceeds of a total of $19.4 million (£15.5 million) through the issue of 89.1 million new Ordinary Shares of £0.003 each in the Company at a price of 17.4 pence per share and proceeds of a total of $50.6 million (£40.5 million) through the issue by the Company of convertible notes (the “Tranche 1 Notes”). The Purchasers also received conditional warrants to subscribe for further Ordinary Shares (the “Warrants”). The ability for the Tranche 1 Notes to be converted into Ordinary Shares and for the Warrants to be exercised is conditional on the passing of certain resolutions (the “Resolutions”) at a general meeting of shareholders scheduled for June 30, 2020 (the “General Meeting”). If the Resolutions are passed, the Tranche 1 Notes will automatically convert into Ordinary Shares at 17.4p, subject to limitations that apply to the percentage of voting shares that may be held by Purchasers. Any Tranche 1 Notes not so converted will remain outstanding. The Tranche 1 Notes will not be separately admitted to trading on AIM, but the Ordinary Shares which will arise following any valid conversion of the Tranche 1 Notes will be admitted to trading as part of the Company’s single class of shares admitted to trading on AIM or the relevant exchange on which the Company’s shares are traded at the time the Tranche 1 Notes are converted. The Board estimates that 21,674,143 Tranche 1 Notes will convert automatically if the Resolutions are passed on June 30, 2020, resulting in 124,564,033 Ordinary Shares (excluding Ordinary Shares resulting in respect of interest on the converted Tranche 1 Notes) being issued, leaving 18,859,528 Tranche 1 Notes in issue. If the Resolutions are not passed on or before 7 August 2020 the convertible notes will not convert into ordinary shares, the warrants will not become capable of exercise and the holders of the convertible notes and warrants will become entitled to certain amounts up to £137.1 million that will represent material liabilities for the Company. The Purchasers, representing in aggregate approximately 40 per cent. of the Company’s total number of shares and votes have undertaken to vote in favour of the Resolutions relating to the warrants and the convertible notes. The Tranche 1 Notes are constituted by the Note Instrument, details of which are set out below. The Warrants are constituted by the Warrant Instrument, details of which are also set out below. Note Instrument The Note Instrument constitutes three potential tranches of Loan Note: • an initial tranche of 40,533,671 Tranche 1 Notes representing $50.6 million (£40.5 million) issued to all Purchasers; • a second tranche of up to £40.0 million Tranche 2 Notes representing approximately 115,034,554 ordinary shares which may be issued following the third anniversary of the date on which the Resolutions are passed to certain holders of Tranche 1 Notes in lieu of the holder exercising its subscription rights under the Warrants and in return for payment by that holder of the aggregate exercise price of the relevant Warrants; and • a third tranche of up to £56.0 million Tranche 3 Notes, which may be issued, if the Resolutions are not passed at the General Meeting (or at any subsequent general meeting) held on or before August 7, 2020. The Tranche 1 Notes have a maturity date of June 2023 unless otherwise extended, converted or accelerated. The Tranche 2 Notes have a maturity date of three years from their date of issue (i.e. such that they would be anticipated as becoming due in 2026) unless otherwise extended, converted or accelerated. The Tranche 3 Notes have a maturity date of August 2025 unless otherwise extended, converted or accelerated. The Tranche 1 Notes and Tranche 2 Notes may be extended by certain holders beyond the initial maturity date to have a longstop maturity date of 10 years from the date of the Note Instrument. Tranche 3 Notes may also be extended by certain holders beyond the initial maturity date up to the same longstop maturity date of 10 years from the date of the Loan Note Instrument, however, such extension is subject to the consent of the Company. Tranche 1 Notes will initially bear interest at a fixed rate of 10 per cent. per annum, which will be retroactively reduced to a rate of 6 per cent. per annum to the date of issue if the Resolutions are passed on or before August 7, 2020. If the Tranche 1 Notes are extended, they cease to bear interest from that extension. Tranche 2 Notes and Tranche 3 Notes do not accrue interest (unless default interest applies). Following an event of default by the Company, default interest will accrue on all Loan Notes at 2 per cent. above the applicable interest rate in force at that time for the relevant Loan Notes. All the Loan Notes are unsecured and have been contractually subordinated to the Company’’s existing senior debt facility with Silicon Valley Bank and Kreos Capital pursuant to the terms of a Subordination Agreement to which all Purchasers have acceded as part of the Fundraising. If the Resolutions are not passed on or before August 7, 2020, the holders of Tranche 1 Notes are entitled to an additional fee (the “Uplift Payment”). The Uplift Payment is designed to compensate the Tranche 1 Noteholders for being unable to participate in the equity of the Company through the conversion of the Tranche 1 Notes and the exercise of Warrants. The value of the Uplift Payment for each Purchaser shall be equal to the aggregate principal amount of the Loan Notes held by such Purchaser on August 7, 2020. Any Purchaser who fails to attend the General Meeting (in person or by proxy) and vote in favour of the Resolutions relating to the Warrants and the Tranche 1 Notes shall not be entitled to the Uplift Payment. Any Uplift Payment if due, is payable on the redemption date of the relevant Loan Notes. If the Resolutions are not passed on or before August 7, 2020, an original holder of the Warrants may elect without payment to convert its Warrants into fully paid Tranche 3 Notes with a principal amount equal to the aggregate exercise price (being 34.8 pence per Warrant Share) of those Warrants, in compensation for the right to exercise those Warrants not having arisen. If the Resolutions have not been passed at a time when the Company undergoes a change of control, each Noteholder on the date of such change of control, shall (to the exclusion of the Uplift Payment) be entitled to a payment equal to the amount of consideration they would have received on such change of control had the Resolutions been passed and they had received their full entitlement of Ordinary Shares and all Warrants they held had become exercisable, less the aggregate principal and interest outstanding on the Tranche 1 Notes and certain residual interests in the Warrants (if any) they held on the date of the change of control (the “Change of Control Payment”). Until the Resolutions have been passed, no Tranche 1 Notes are capable of conversion. If the Resolutions are passed on or before August 7, 2020, the Tranche 1 Notes will automatically convert into Ordinary Shares, except that no new Ordinary Shares will be issued which would result in any person holding in excess of 9.99 per cent. of the aggregate voting rights in the Company as a result of the relevant conversion. Any Tranche 1 Notes not converted will remain outstanding. After the Resolutions have been passed, those Tranche 1 Notes not automatically converted and any Tranche 2 Notes that may be issued, will be convertible into Ordinary Shares at the election of the Noteholders at any time prior to their maturity date, and subject to the 9.99 per cent. beneficial ownership limit. The Tranche 3 Notes are not capable of conversion. The Loan Notes are required to be repaid on the earlier of (i) the applicable maturity date; and (ii) a change of control taking place in respect of the Company, and are otherwise not able to be prepaid other than with the consent of a noteholder majority, or if accelerated following an event of default. The Loan Notes are subject to customary events of default (for example, insolvency events in respect of the Company and default under the Company’s material contracts, amongst others) and any principal amount and interest outstanding is capable of being accelerated following the occurrence of such an event of default and the expiry of any cure periods applicable thereto. Warrants All the participants in the Fundraising have received conditional warrants to subscribe for further Ordinary Shares in an aggregate number equal to 50 per cent. of both the Ordinary Shares purchased in the Fundraising and the Ordinary Shares initially issuable upon conversion of the Tranche 1 Notes. A total of 161,048,366 Warrants have been issued. The Warrants have an exercise price of 34.8 pence per Ordinary Share, which is equal to 200 per cent. of the Fundraising issue price, and will be capable of being exercised at any time from and after the date the Resolutions are passed at the General Meeting (or at any subsequent general meeting) until the third anniversary of the date the Resolutions are passed. The Warrants can be exercised for cash or on a cashless basis. If the Resolutions are not passed at the General Meeting (or at any subsequent general meeting), the Warrants remain non-exercisable but will, until August 8, 2025, continue to benefit from rights to participate in certain transactions. These include if the Company is acquired, following which the Company is required to use its best efforts to ensure that Warrant holders receive alternate warrants in the acquirer. In certain circumstances, Warrant holders may require the Company (or the acquirer) pay them (to the extent lawful) the value of the Warrants, determined in accordance with a Black-Scholes valuation provision. The Warrant exercise price and the number of shares issuable upon exercise of the Warrants will be adjusted in certain circumstances, including if the Company effects a subdivision or consolidation of its Ordinary Shares, declares a dividend or distribution, or there is a reorganisation of its Ordinary Shares. Arrangements with OrbiMed In recognition of OrbiMed’s participation in, and assistance with, the Fundraising, the Company has agreed to grant OrbiMed certain rights. OrbiMed will have the right to nominate two persons to be appointed to the Board of Directors (out of a maximum number of 9 directors), within a period of 180 days of the fundraising subject to the appropriateness of the nominees. OrbiMed has also been granted the right to participate in future financings of the Company, subject, amongst other things, to the existing pre-emption rights of the Shareholders under the Companies Act 2006 and certain existing agreements to which the Company is a party. OrbiMed has been paid a subscription fee of $325,000 by the Company by way of a commission in consideration of its participation in the Fundraising.

Significant accounting polici_2

Significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2019
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Basis of preparation	2.1 Basis of preparation The Group’s consolidated financial statements have been prepared in accordance with International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). The financial statements are presented in pound sterling (“£’000”), which is the functional and presentational currency of the Group. All amounts disclosed in the financial statements and notes have been rounded off to the nearest thousand currency units, unless otherwise stated.
Revision of previously issued financial statements	2.2 Revision of previously issued financial statements During 2019, we identified a classification error in our statement of comprehensive loss for the year ended December 31, 2018 related to loan modification expense. In correcting the error, administrative expenses reduced by £0.7 million and finance charges increased by an equivalent amount. There was no impact on net loss. We evaluated the materiality of the error quantitatively and qualitatively and concluded it was not material to our previously issued Consolidated Financial Statements as a whole for the year ended and as of December 31, 2018. Please refer to Financial statement notes 9 and 19.
Basis of consolidation	2. 3 The consolidated financial information comprises the financial statements of Mereo BioPharma Group plc and its subsidiaries as at December 31, 2019. Subsidiaries are all entities over which the Group has control. The Group controls an entity when the Group is exposed to, or has rights to, variable returns from its involvement with the entity and has the ability to affect those returns through its power over the entity. Subsidiaries are fully consolidated from the date on which control is transferred to the Group. They are deconsolidated from the date that control ceases. Intercompany transactions, balances and unrealized gains on transactions between Group companies are eliminated in preparing the consolidated financial statements. Accounting policies of subsidiaries are consistent with the policies adopted by the Group. The Company has an employee share trust to facilitate share transactions pursuant to employee share schemes. Although the trust is a separate legal entity from the Group, it is consolidated into the Group’s results in accordance with the IFRS 10 rules on special purpose vehicles. The Company is deemed to control the trust principally because the trust cannot operate without the funding the Group provides.
Segmental information	2. 4 Management views the Group as a single portfolio of product candidates. Only research and development expenses are monitored at a product candidate level, however the Chief Operating Decision Maker (“CODM”) makes decisions over resource allocation at an overall portfolio level. The Group’s financing is managed and monitored on a consolidated basis. Following the acquisition of OncoMed during the year, non-current non-current The Group’s CODM is the executive leadership team which is comprised of several individuals including the Chief Executive Officer (“CEO”) and Chief Financial Officer (“CFO”). The executive leadership team is responsible for managing the operating results of the business. The operations of the Group are mostly influenced by the timing of progression on underlying clinical development programmes across product candidates which remain under development.
Going concern	2.5 Going concern As at May 31, 2020 the group had total cash resources* £10.1 million. Taken together with the private placement which completed on June 3, 2020 and which raised net proceeds of approximately £51.4 million, the group has current total cash resources of £61.5 million. The Directors have prepared detailed cashflow forecasts for the 30-month period to December 31, 2022 based on delivering the business plan objectives set out in the strategic report which include: • Completion of the adult Phase 2b extension study for setrusumab • Completion of the current Phase 2 study for alvelestat • Commencement later in 2020 of a new Phase 1b study for etiligimab These forecasts indicate that the group has a total cash runway into 2022 and will have sufficient funds to meet its liabilities as they fall due for at least the next 12 months. In preparing these forecasts the directors have considered the impact of COVID-19 and in particular the unprecedented burden on health systems in impacted countries around the world. As a result, clinical centres have diverted resources away from the performance of clinical trials and because of that and the vulnerability of patients in the Company’s setrusumab clinical development program for osteogenesis imperfecta (OI) and its Phase 2 alvelestat program for patients with alpha-1 antitrypsin deficiency (AATD), the Company’s clinical activities will face some delays. AATD patients, in particular, are at greater risk from COVID-19 given that the condition is a respiratory and lung condition, for this reason, our Phase 2 alvelestat trial will be delayed with topline data now expected in 2021. Subject to a partnership, we are also currently planning to initiate a Phase 3 study in children with OI in late 2020, however, the initiation of the study may also be delayed. In addition, the Directors have considered a downside scenario involving an increase in operating overheads, an increase in the costs of setting up and running the planned Phase 1b study for etiligimab when this study is contracted out to third parties and increased investment in manufacturing development costs for setrusumab. In addition, In this scenario the forecasts also indicate that the group will have sufficient funds to meet its liabilities as they fall due for at least the next 12 months. In both scenarios the Directors have not taken into account potential income from partnering one or more of its assets which would increase the cash resources available to the Group In conclusion, although the Group continues to make losses, the directors believe it is appropriate to prepare the financial information on the going concern basis. This is because the Group’s development into new products continues to progress according to plan and the funding secured to date, together with the funds that have come into the Group since the year end (as described more fully in Note 30) will allow it to meet its liabilities as they fall due for at least 12 months from the date of authorization for the issue of these consolidated financial statements. • Total cash resources are a non-GAAP measure being cash and short-term deposits and short-term investments
Taxes	a) Taxes Tax expense recognized in the statement of comprehensive income comprises the sum of deferred tax and current tax not recognized in other comprehensive income or directly in equity Current income tax Current income tax assets and / or liabilities are measured at the amount expected to be recovered from or paid to the taxation authorities that are unpaid at the reporting date. Current tax is payable on taxable profit, which differs from profit or loss in the financial statements. Calculation of current tax is based on tax rates and tax laws that have been enacted or substantively enacted by the end of the reporting period within the jurisdictions that the Group operates in. Amounts receivable in respect of research and development tax credits are recognized in the financial statements provided there is sufficient evidence that the amounts are recoverable. These credits are recognized within income tax in the consolidated statement of comprehensive loss. Deferred tax Deferred tax is provided using the liability method on temporary differences between the tax bases of assets and liabilities and their carrying amounts for financial reporting purposes at the reporting date. Deferred income tax assets are recognized for all deductible temporary differences, carry-forward of unused tax credits and unused tax losses, to the extent that it is probable that taxable profit will be available against which the deductible temporary differences and the carry-forward of unused tax credits and unused tax losses can be utilized. The carrying amount of deferred income tax assets is reviewed at the end of each reporting period and reduced to the extent that it is no longer probable that sufficient taxable profit will be available to allow all or part of the deferred income tax asset to be utilized. Unrecognized deferred income tax assets are reassessed at the end of each reporting period and are recognized to the extent that it has become probable that future taxable profit will allow the deferred tax asset to be recovered. Deferred tax assets and liabilities are measured on an undiscounted basis at the tax rates that are expected to apply to the year when the asset is realized, based on tax rates (and tax laws) enacted or substantively enacted at the end of the reporting period. IFRIC 23, Uncertainty over Income Tax Treatments In June 2017, the IASB issued IFRIC Interpretation 23, Uncertainty over Income Tax Treatments (IFRIC 23), which addresses how uncertain tax positions should be accounted for under IFRS. IFRIC 23 requires that, where acceptance of the tax treatment by the relevant tax authority is considered probable, it should be assumed as an accounting recognition matter that treatment of the item will ultimately be accepted. Therefore, no tax provision would be required in such cases. However, if acceptance of the tax treatment is not considered probable, the entity is required to reflect that uncertainty using an expected value (i.e., a probability-weighted approach) or the single most likely amount. IFRIC 23 is mandatorily effective for accounting periods beginning on or after 1 January 2019 and any resulting change to the tax provisions should be recognized in retained earnings. Mereo has recognized a net tax expense of nil in retained earnings on 1 January 2019 in respect of the adoption of IFRIC 23.
Foreign currencies	b) Foreign currencies Items included in the financial statements are measured using the curren cy Transactions in foreign currencies are initially recorded by the Group’s entities at the rate ruling on the date the transaction first qualifies for recognition. Differences arising on settlement or translation of monetary items are recognized in the consolidated statement of comprehensive loss, as well as gains or losses on the retranslation of foreign currency balances at the year end. The results and financial position of Group entities that have a functional currency different from the presentational currency of the Group are translated into the presentational currency (pound sterling). The assets and liabilities of such entities are translated into pound sterling at the rate of exchange ruling at the balance sheet date. Income and expenses are translated at the average rate for the period. Fair value adjustments arising on acquisition of such entities are treated as assets and liabilities of the relevant entity and translated into pound sterling at the closing rate. The exchange differences arising on translation for consolidation are recognized in other comprehensive income.
Property, plant and equipment	c) Property, plant and equipment Property, plant and equipment is stated at cost, net of accumulated depreciation and accumulated impairment losses, if any. Such cost includes the cost of replacing part of the plant and equipment if the recognition criteria are met. All other repair and maintenance costs are recognized in profit or loss as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the assets, as follows: • Leasehold improvements ten years • Office equipment five years • IT equipment three years The right-of-use property, plant and equipment. Right-of-use • Right-of-use asset (building) six to nine years • Right-of-use asset (equipment) one to two years An item of property, plant and equipment and any significant part initially recognized is derecognized upon disposal or when no future economic benefits are expected from its use or disposal. Any gain or loss arising on derecognition of the asset (calculated as the difference between the net disposal proceeds and the carrying amount of the asset) is included in the statement of comprehensive loss when the asset is derecognized. The residual values, useful lives and methods of depreciation of property, plant and equipment are reviewed at each financial year end and adjusted prospectively, if appropriate.
Business combinations	d) Business combinations Business combinations are accounted for using the acquisition method of accounting. At the date of the acquisition, the Group initially recognizes the fair value of the identifiable assets acquired, the liabilities assumed and any non-controlling interest in the acquired business. The consideration transferred is measured at fair value at the date acquisition. The excess of the consideration transferred over the fair value of net identifiable assets of the business acquired is recorded as goodwill, unless the amount of consideration transferred is less than the fair value of net identifiable assets of the business acquired in which case the difference is recognized directly in the consolidated statement of comprehensive loss as a bargain purchase. A valuation is performed of assets and liabilities assumed on each acquisition accounted for as a business combination based on our best estimate of fair value. Where the settlement of any part of cash consideration is deferred, the amounts payable in the future are discounted to their present value. Contingent consideration is classified either as equity or a financial liability and is recognized at fair value on the acquisition date. Amounts classified as a financial liability are subsequently remeasured to fair value in accordance with IFRS 9 (Financial Instruments), with changes in fair value recognized in the consolidated statement of comprehensive loss as an administrative expense. Directly attributable acquisition-related costs are expensed as incurred within the consolidated statement of comprehensive loss.
Leases	d) Leases (IFRS 16) Effective January 1, 2019, the Group implemented IFRS 16 (Leases). IFRS 16 (Leases) replaces existing guidance, including IAS 17 ( L For further information, refer to Note 4.
Intangible assets	e) Intangible assets Intangible assets are initially recorded at cost which has been determined as the fair value of the consideration paid and payable. Assets that have been acquired through a business combination are initially recorded at fair value. The fair value of consideration is regularly reviewed based on the probability of achieving contractual milestones. Intangible assets are reviewed for impairment at each reporting date by allocating the assets to the cash-generating units to which they relate. The estimated useful life is the lower of the legal duration and economic useful life. The estimated useful lives of intangible assets are regularly reviewed on an at least annual basis. Where the consideration paid or payable is in shares, the cost is measured in accordance with IFRS 2 (Share Based Payments). Amortization would commence when product candidates underpinned by the intangible asset become available for commercial use. No amortization has been charged to date, as the product candidates underpinned by the intellectual property rights are not yet available for commercial use.
Financial instruments	f) Financial instruments Financial assets and liabilities are recognized in the consolidated balance sheet only when the Group becomes party to the contractual provisions of the instrument. Financial assets On initial recognition, a financial asset is classified into one of three primary measurement categories: • Amortized cost; • Fair value through OCI (“FVOCI”); or • Fair value through profit or loss (“FVTPL”). The initial classification into a primary measurement category depends on the nature and purpose of the financial asset. For each reporting period covered herein, the Group’s financial assets were restricted to financial assets held at FVOCI. This relates to short-term investments which are not classified as cash and short-term deposits and are held in a business model whose objective is achieved by both collecting contractual cash flows and selling the short-term investment on maturity. For short-term investments, interest income and impairment gains or losses are recognized directly in the consolidated statement of comprehensive loss. The difference between cumulative fair value gains or losses and the cumulative amounts recognized in the consolidated statement of comprehensive loss is recognized in other comprehensive income until derecognition, when the amounts in other comprehensive income are reclassified to the consolidated statement of comprehensive loss.
Fair value measurement	g) Fair value measurement Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value measurement is based on the presumption that the transaction to sell the asset or transfer the liability takes place either: • In the principal market for the asset or liability; or • In the absence of a principal market, in the most advantageous market for the asset or liability. The principal or the most advantageous market must be accessible by the Group. The fair value of an asset or a liability is measured using the assumptions that market participants would use when pricing the asset or liability, assuming that market participants act in their economic best interest. The Group uses valuation techniques that are appropriate in the circumstances and for which sufficient data are available to measure fair value, maximizing the use of relevant observable inputs and minimizing the use of unobservable inputs. All assets and liabilities for which fair value is measured or disclosed in the financial statements are categorized within the fair value hierarchy, described as follows, based on the lowest level input that is significant to the fair value measurement as a whole: • Level 1 — quoted (unadjusted) market prices in active markets for identical assets or liabilities. • Level 2 — valuation techniques for which the lowest level input that is significant to the fair value measurement is directly or indirectly observable. • Level 3 — valuation techniques for which the lowest level input that is significant to the fair value measurement is unobservable. For assets and liabilities that are recognized in the financial statements on a recurring basis, the Group determines whether transfers have occurred between levels in the hierarchy by reassessing categorization (based on the lowest level input that is significant to the fair value measurement as a whole) at the end of each reporting period.
Impairment of non-financial assets	h) Impairment of non-financial Further disclosures relating to impairment of non-financial • Disclosures for significant assumptions Note 3 • Property, plant and equipment Note 12 • Intangible assets not yet available for use Notes 13 and 14 The Group assesses, at each reporting date, whether there is an indication that an asset may be impaired. If any indication exists, or when annual impairment testing for an asset is required, the Group estimates the asset’s recoverable amount. An asset’s recoverable amount is the higher of an asset’s or cash-generating unit’s fair value less costs of disposal and its value in use. The recoverable amount is determined for an individual asset, unless the asset does not generate cash inflows that are largely independent of those from other assets or groups of assets. When the carrying amount of an asset or cash-generating unit exceeds its recoverable amount, the asset is considered impaired and is written down to its recoverable amount. In assessing value in use, the estimated future cash flows are discounted to their present value using a pre-tax Impairment losses are recognized in the statement of comprehensive loss in expense categories consistent with the function of the impaired asset. An assessment is made at each reporting date to determine whether there is an indication that previously recognized impairment losses no longer exist or have decreased. If such indication exists, the Group estimates the asset’s or cash-generating unit’s recoverable amount. A previously recognized impairment loss is reversed only if there has been a change in the assumptions used to determine the asset’s recoverable amount since the last impairment loss was recognized. The reversal is limited so that the carrying amount of the asset does not exceed its recoverable amount, nor exceed the carrying amount that would have been determined, net of depreciation, had no impairment loss been recognized for the asset in prior years. Such reversal is recognized in the statement of comprehensive loss unless the asset is carried at a revalued amount, in which case the reversal is treated as a revaluation increase.
Cash and short-term deposits	i) Cash and short-term deposits Cash and short-term deposits in the balance sheet comprise cash at banks and on hand and short-term deposits with a maturity of three months or less, which are subject to an insignificant risk of changes in value.
Short-term investments	j) Short-term investments Cash held on deposit for terms greater than three months are recognized at fair value in the balance sheet with fair value changes recognized in other comprehensive income. Interest revenue, impairment gains and losses, and a portion of foreign exchange gains and losses, are recognized in profit and loss. When the short-term investment is derecognized or reclassified, changes in fair value previously recognized in other comprehensive income and accumulated in equity are reclassified to profit and loss.
Provisions	k) Provisions Provisions are recognized when the Group has a present obligation (legal or constructive) as a result of a past event, it is probable that an outflow of resources embodying economic benefits will be required to settle the obligation and a reliable estimate can be made of the amount of the obligation. When the Group expects some or all of a provision to be reimbursed, for example, under an insurance contract, the reimbursement is recognized as a separate asset, but only when the reimbursement is virtually certain. The expense relating to a provision is presented in the statement of comprehensive loss net of any reimbursement. If the effect of the time value of money is material, provisions are discounted using a current pre-tax
Share-based payments	l) Share-based payments Employees (including executives) of the Group receive remuneration in the form of share-based payments, whereby employees render services as consideration for equity instruments (equity settled transactions). Incentives in the form of shares are provided to employees under various plans (Note 26). Executive officer have outstanding shares under a deferred bonus share plan (“DBSP Plan”) and a long-term incentive plan (“LTIP Plan”). In accordance with IFRS 2 Share-based Payment (“IFRS 2”), charges for these incentives are expensed through the consolidated statement of comprehensive loss on a straight-line basis over their vesting period, based on the Group’s estimate of shares that will eventually vest. The total amount to be expensed is determined by reference to the fair value of the options or awards at the date they were granted. For LTIP shares, the fair value on grant date excludes the impact of any non-market vesting conditions – these are instead taken into account by adjusting the number of equity instruments included in the measurement of the share-based payment transaction and are adjusted each period until such time as the equity instruments vest. Share options awarded to non-employees are accounted for as options awarded to employees as the value of non-employee services could be readily determined. In accordance with IFRS 2, the cancellation of share options is accounted for as an acceleration of the vesting period and therefore any amount unrecognized that would otherwise have been charged in future accounting periods is recognized immediately. When options are forfeited, the accounting expense for any unvested awards is reversed. Purchases, where consideration is satisfied by issuing equity shares, is accounted for as equity settled share-based payment transactions in accordance with IFRS 2. Fair value is determined by the share price at the date of purchase.
Costs of issuing capital	m) Costs of issuing capital Incremental costs incurred and directly attributable to the offering of equity securities are deducted from the related proceeds of the offering. The net amount is recorded as share premium in the period when such shares are issued. Where such expenses are incurred prior to the offering they are recorded in prepayments until the offering completes. Other costs incurred in such offerings are expensed as incurred and included in general and administrative expenses.
Convertible loan instrument	n) Convertible loan instrument Convertible loan notes are regarded as compound instruments consisting of a liability component and an equity component. At the date of issue, the fair value of the liability component is estimated using a discount rate for an equivalent liability without the conversion feature. The difference between the proceeds of issue of the convertible loan note and the fair value assigned to the liability component is included in equity.
Employee Benefit Trust	o) Employee Benefit Trust The Group operates an Employee Benefit Trust (“EBT”), the Mereo BioPharma Group plc Employee Benefit Trust. The EBT has been established to fulfil awards made under the DBSP Plan and the LTIP Plan. The EBT is a Jersey-based trust which is funded by a loan from the Company, which it will utilize to buy shares at nominal value from the Company in sufficient quantity to fulfil the envisaged awards. The EBT will acquire shares in the Company and these will be deducted from the shareholders’ funds on the consolidated balance sheet at the cost of acquisition less proceeds on disposal. Shares held by the EBT are included in the consolidated balance sheet as a reduction in equity. The Group treats the EBT as an extension of the Group and the Company as it is ultimately controlled by the Company and therefore consolidated.
Research and development	p) R&D costs Expenditure on product development is capitalized as an intangible asset and amortized over the expected useful economic life of the product candidate concerned. Capitalization commences from the point at which technical feasibility and commercial viability of the product candidate can be demonstrated and the Group is satisfied that it is probable that future economic benefits will result from the product candidate once completed. Capitalization ceases when the product candidate receives regulatory approval for launch. No such costs have been capitalized to date. Expenditure on R&D activities that do not meet the above criteria, including ongoing costs associated with acquired intellectual property rights and intellectual property rights generated internally by the Group, is charged to the statement of comprehensive loss as incurred. Intellectual property and in-process R&D from asset acquisitions are recognized as intangible assets at cost.
Provision for deferred cash consideration	q) Provision for deferred cash consideration Provision for deferred cash consideration consists of future payments which are contractually committed but not yet certain. In respect of products which are not yet approved, such deferred cash consideration excludes potential milestones, royalties or other payments that are deemed to be so uncertain as to be unquantifiable. Deferred cash consideration is recognized as a liability with the amounts calculated as the risk adjusted net present value of anticipated deferred payments. The provision is reviewed at each balance sheet date and adjusted based on the likelihood of contractual milestones being achieved and therefore the deferred payment being settled. Increases in the provision relating to changes in the probability are recognized as an intangible asset. Increases in the provision relating to the unwinding of the time value of money are recognized as a finance expense.
Bank loan and associated warrants	r) Bank loan Borrowings (including interest-bearing loans) are initially recognized at fair value, net of transaction costs incurred. Borrowings are subsequently measured at amortized cost. Any difference between the proceeds (net of transaction costs) and the redemption amount is recognized in profit or loss over the period of the borrowings using the effective interest method. Under the effective interest method, amortization is included as a finance charge in the consolidated statement of comprehensive loss. The Group’s policy is to account for non-substantial modifications to financial liabilities measured at amortized cost through a gain or loss which is recorded in the consolidated statement of comprehensive loss. The gain or loss is calculated as the difference between the original contractual cash flows and the modified cash flows, discounted at the original effective interest rate. For substantial modifications, the Group’s policy is to derecognize the existing financial liability and in turn recognize a new financial liability. Borrowings are removed from the balance sheet when the obligation specified in the contract is discharged, cancelled or expired. s) Associated warrants The Group has issued certain warrant instruments to its lenders (Note 19). As the terms of the warrant instruments allow for a cashless exercise, the Group’s policy is to account for the associated warrant instruments at fair value with changes in the fair value recognized in the consolidated statement of comprehensive loss (see Note 21).
The Alpha-1 Project (TAP) funding agreement and associated warrants	t) The Alpha-1 Project (TAP) funding agreement and associated warrants The agreement is accounted for as a compound instrument which includes both debt and equity components. The liability is measured first at fair value and the residual value allocated to the equity component. The difference between the funding payment amount received and the measurement of the liability will be allocated to the warrants and recognized in equity. The value of warrants in equity will not be subsequently remeasured as the warrants will be settled by providing a fixed number of shares for a fixed amount of cash.

Significant accounting polici_3

Significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2019
Statement [line items]
Summary of Depreciation Calculated on Straight-Line Basis Over Estimated Useful Lives of Assets	Depreciation is calculated on a straight-line basis over the estimated useful lives of the assets, as follows: • Leasehold improvements ten years • Office equipment five years • IT equipment three years
Property, plant and equipment subject to operating leases [member]
Statement [line items]
Summary of Depreciation Method For Property Plant And Equipment And Useful Life	• Right-of-use asset (building) six to nine years • Right-of-use asset (equipment) one to two years

Changes in accounting policies

Changes in accounting policies (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of adjustments recognised at the date of initial application of IFRS 16	The table below sets out the adjustments recognized at the date of initial application of IFRS16, which does not include the leases acquired as part of the OncoMed acquisition. As at Impact of Restated as January 1, Non-current Property, plant and equipment 149 2,552 2,701 Prepayments and other 1,067 (50 ) 1,017 Total impact on assets 2,502 Current liabilities Trade and other payables 4,570 — 4,570 Lease liabilities — 607 607 Non-current Lease liabilities — 1,927 1,927 Accruals 4,437 (32 ) 4,405 Total impact on liabilities (2,502 ) Total impact on retained earnings —
Summary of reconciliation from operating lease commitments	The table below presents a reconciliation from operating lease commitments disclosed as at December 31, 2018 to lease liabilities recognized as at January 1, 2019. Operating lease commitments disclosed under IAS 17 (at December 31, 2018) 536 Effect of discounting (944 ) Reassessment of lease term under IFRS 16 2,942 Lease liabilities recognised under IFRS 16 (at January 1, 2019) 2,534
Summary of relation to leases under IFRS 16 the Group	As at December 31, 2019, in relation to leases under IFRS 16 ( Leases ) the Group has recognized the following amounts in the consolidated statement of comprehensive loss: Depreciation 1,505 Interest expense 1,314 Foreign exchange gain 29 Income from sub-leasing right-of-use 855
Summary of Interest-Bearing Loans and Borrowings - Convertible Loan Notes	As a result, under IFRS 9 (Financial Instruments) the carrying value of the convertible loan note as at the date of modification was adjusted to recognize the modification gain in retained earnings as of the date of initial application of January 1, 2018. At January 1, 2018 ( as calculated under IAS 39) 1,977 Amounts restated through retained earnings (124 ) At January 1, 2018 (as calculated under IFRS 9) 1,853

Acquisition of subsidiary (Tabl

Acquisition of subsidiary (Tables)	12 Months Ended
	Dec. 31, 2019
Disclosure of detailed information about business combination [abstract]
Summary of net assets acquired	The final acquisition accounting is set out below: OncoMed Cash and short-term deposits 10,074 Short-term investments 29,019 Other receivables 155 Prepayments 1,699 Property, plant and equipment 82 Right-of-use 10,755 Identifiable intangible assets 12,693 Other liabilities (9,215 ) Lease liabilities (10,689 ) Net identifiable assets 44,573 Bargain purchase (3,681 ) Total consideration 40,892 Equity instruments (24.8 million ordinary shares) 40,892 Contingent consideration arrangement — Total consideration 40,892

Group information (Tables)

Group information (Tables)	12 Months Ended
	Dec. 31, 2019
Investments accounted for using equity method [abstract]
Summary of Information About Subsidiaries of the Group	The consolidated financial statements of the Group include: Name Principal activities Country of % equity December 31, 2019 % equity Mereo BioPharma 1 Limited Pharmaceutical R&D U.K. 100 100 Mereo BioPharma 2 Limited Pharmaceutical R&D U.K. 100 100 Mereo BioPharma 3 Limited Pharmaceutical R&D U.K. 100 100 Mereo BioPharma 4 Limited Pharmaceutical R&D U.K. 100 100 Mereo BioPharma Ireland Limited Pharmaceutical R&D Ireland 100 100 OncoMed Pharmaceuticals, Inc. Pharmaceutical R&D U.S. 100 — Navi Subsidiary, Inc. Pharmaceutical R&D U.S. 100 — Mereo US Holdings Inc. Holding company U.S. 100 100 Mereo MergerCo One Inc. Holding company U.S. — 100 Mereo BioPharma Group plc Employee Benefit Trust Employee share scheme Jersey — —

Loss before taxation (Tables)

Loss before taxation (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule Of Detailed Information About Loss Before Taxation [Abstract]
Summary of Loss before tax is stated after charging	Loss before tax is stated after charging: Year ended December 31, 2018 Year ended 9 Fees payable to the Company’s Auditor for the audit of Group accounts 323 514 Fees payable to the Company’s Auditor for other services: Audit of subsidiary accounts 30 45 Audit-related assurance services 171 311 Accounting advisory services 10 — Legal and professional fees including patent costs 936 2,413 Operating lease expense (IAS 17) 293 — Depreciation of right-of-use — 1,505 Depreciation (excluding right-of-use 40 52

Employees (Tables)

Employees (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Average Monthly Persons Employed By Group	The average monthly number of persons employed by the Group (including Directors) during the year was: Year ended 8 Year ended 9 By activity Administrative 24 28 Research and development 12 18 Total 36 46
Summary of Employee	Total compensation costs for persons employed by the Group (including Directors) during the year was: Year ended 8 Year ended 9 Included in research and development expenses: Salaries 1,792 2,824 Social security costs (30 ) 110 Pension contributions 73 62 Share-based payment expense 526 152 Included in administrative expenses: Salaries 2,903 3,384 Social security costs (828 ) (124 ) Pension contributions 99 114 Share-based payment expense 1,663 1,485 Total employee benefits expense 6,198 8,007
Summary of Compensation Cost For Directors	Total compensation costs for Directors during the year was: Year ended 8 Year ended 9 Salaries and fees 1,047 1,106 Benefits in kind 15 17 Pension contributions 11 25 Bonus 512 294 Total 1,585 1,442

Other income _ expenses and a_2

Other income / expenses and adjustments (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Finance Income	Finance income Year ended December 31 2017 2018 2019 Bank interest earned 827 307 42 Interest earned on short-term investments — — 141 Gain on short-term investments — — 194 Total finance income 827 307 377
Summary of Finance Costs	Finance charge Year ended December 31 2017 2018 2019 Interest payable on convertible loan (103 ) (185 ) (20 ) Interest on TAP funding — — (10 ) Interest payable on bank loan (327 ) (1,645 ) (1,739 ) Interest on lease liabilities — — (1,314 ) Accreted interest on bank loan (67 ) (782 ) (1,523 ) Transaction costs on bank loan (200 ) — — Modification (loss)/gain on bank loan — (730 )* 456 Loss on short-term deposits (339 ) (22 ) — Discounting of provision for deferred cash consideration — (443 ) (221 ) Change in warrant fair value (54 ) 716 875 Total finance charge (1,090 ) (3,091 ) (3,496 ) * We have reclassified the loan modification loss occurring in 2018 resulting in the reduction of administrative expenses by £0.7 million, and the increase in finance charges of an equivalent amount. Please refer

Income tax (Tables)

Income tax (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Income Tax Credit	Year ended December 31 201 7 201 8 201 9 U.K. corporation tax R&D credit 8,152 5,277 5,149 Other tax income / (expense) — — 1,125 Income tax credit 8,152 5,277 6,274
Summary of Reconciliation to the Earnings Loss Per Income Statement	Reconciliation of effective tax rate Year-ended December 31, 2017 2018 2019 Loss on ordinary activities before income tax (46,951 ) (37,306 ) (41,118 ) Loss on ordinary activities before tax at the U.K.’s statutory income tax rate of 19% (2018: 19%) 9,038 7,088 7,812 Expenses not deductible for income tax purposes (permanent differences) (13 ) (1,070 ) (317 ) Temporary timing differences (712 ) (277 ) (343 ) R&D relief uplift 3,447 2,271 2,540 Losses (unrecognized) (3,785 ) (2,804 ) (4,380 ) Deferred income from MBG loan guarantee costs 177 69 (54 ) Differences in overseas tax rates — — 340 Gain on bargain purchase — — 699 Other — — (23 ) Tax credit for the year 8,152 5,277 6,274
Summary of Deferred Tax	The analysis of unrecognized deferred tax is set out below: December 31, 2017 2018 2019 Losses 6,121 8,604 19,443 US tax credits — — 10,032 Accruals — — 947 Fixed assets — — 400 Other — 6 202 Temporary differences trading 2,267 495 4 Net deferred tax asset (unrecognised) 8,388 9,105 31,028
Summary of analysis of recognized deferred tax	The analysis of recognized deferred tax is set out below: At Acquisition Recognized At Deferred tax liabilities Intangible asset — (2,686 ) — (2,686 ) Deferred tax asset Net operating losses — — 2,686 2,686 Net deferred tax asset/(liability) — (2,686 ) 2,686 —

Loss per share (Tables)

Loss per share (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Loss Per Share	December 31, 2017 2018 201 9 Loss £’000 Weighted shares number Loss per share £ Loss £’000 Weighted shares number Loss per share £ Loss £’000 Weighted shares number Loss per share £ Basic and diluted (38,799 ) 69,012,348 (0.56 ) (32,029 ) 71,144,786 (0.45 ) (34,844 ) 89,424,476 (0.39 )

Property, plant and equipment (

Property, plant and equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Property, Plant and Equipment	Right-of-use (building) Right-of-use Leasehold improvements Office equipment IT equipment Total Cost or valuation At January 1, 2019 — — 164 31 71 266 Additions — — — — 21 21 Transition to IFRS 16 (Leases) 1,237 1,314 — — — 2,551 Acquisition of subsidiary (Note 5) 10,755 — — 58 24 10,837 Disposals — — — (18 ) — (18 ) Adjustment to carrying value — (290 ) — — — (290 ) Currency translation effects (115 ) — — — — (115 ) At December 31, 2019 11,877 1,024 164 71 116 13,252 Depreciation and impairment At January 1, 2019 — — (53 ) (16 ) (48 ) (117 ) Disposals — — — — — — Depreciation for the year (996 ) (509 ) (16 ) (14 ) (42 ) (1,577 ) At December 31, 2019 (996 ) (509 ) (69 ) (30 ) (90 ) (1,694 ) Net book value At January 1, 2019 — — 111 15 23 149 At December 31, 2019 10,881 515 95 41 26 11,558 Leasehold improvements Office equipment IT equipment Total Cost or valuation At January 1, 2018 155 30 48 233 Additions 9 1 25 35 Disposals — — (2 ) (2 ) At December 31, 2018 164 31 71 266 Depreciation and impairment At January 1, 2018 (37 ) (10 ) (33 ) (80 ) Disposals — — 2 2 Depreciation for the year (16 ) (6 ) (17 ) (39 ) At December 31, 2018 (53 ) (16 ) (48 ) (117 ) Net book value At January 1, 2018 118 20 15 153 At December 31, 2018 111 15 23 149 Leasehold improvements Office equipment IT equipment Total Cost or valuation At January 1, 2017 155 20 43 218 Additions — 10 5 15 Disposals — — — — At December 31, 2017 155 30 48 233 Depreciation and impairment At January 1, 2017 (21 ) (5 ) (18 ) (44 ) Disposals — — — — Depreciation for the year (16 ) (5 ) (15 ) (36 ) At December 31, 2017 (37 ) (10 ) (33 ) (80 ) Net book value At January 1, 2017 134 15 25 174 At December 31, 2017 118 20 15 153

Intangible assets (Tables)

Intangible assets (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Detailed Information about Intangible Assets	Acquired development programs Cost at January 1, 2018 33,005 Cost at December 31, 2018 33,005 Acquisition of subsidiary (Note 5) 12,693 Currency translation effects (171 ) Cost at December 31, 2019 45,527 Revision to estimated value at January 1, 2018 — Revisions to estimated value (373 ) Revision to estimated value at December 31, 2018 (373 ) Revision to estimated value (698 ) Revision to estimated value at December 31, 2019 (1,071 ) Net book value at January 1, 2018 33,005 Net book value at December 31, 2018 32,632 Net book value at December 31, 2019 44,456 Acquired development programs Cost at January 1, 2017 25,813 Cost at December 31, 2017 33,005 Cost at December 31, 2018 33,005 Revision to estimate value at January 1, 2017 — Revisions to estimated value — Revision to estimated value at December 31, 2017 — Revision to estimated value (373 ) Revision to estimate value at December 31, 2018 (373 ) Net book value at January 1, 2017 25,813 Net book value at December 31, 2017 33,005 Net book value at December 31, 2018 32,632

Impairment testing of acquire_2

Impairment testing of acquired development programs not yet available for use (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Carrying Amount of Acquired Development Programs	The carrying amount of acquired development programs is as follows: As at December 31, 2019 Navicixizumab BPS-804 MPH-966 BGS-649 BCT-197 Total Acquired development programs 12,522 11,616 6,121 9,886 4,311 44,456 As at December 31, 2018 BPS-804 MPH-966 BGS-649 BCT-197 Total Acquired development programs 11,616 6,819 9,886 4,311 32,632

Other receivables (Tables)

Other receivables (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Other Receivables	December 31, 2018 2019 Rent deposit 293 293 VAT recoverable 316 269 Other receivables — 10 609 572

Cash and short-term deposits (T

Cash and short-term deposits (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Cash and Short-term Deposits	December 31, 2018 2019 Cash at banks and on hand 5,344 15,803 Short-term deposits 19,698 544 25,042 16,347

Short-term investments (Tables)

Short-term investments (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Short-term Investments	December 31, 2018 2019 Short-term investments 2,500 —

Issued capital and reserves (Ta

Issued capital and reserves (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Detailed Information of Ordinary Share Capital	Ordinary share capital 2017 Balance at beginning of year 193 Issuances in the year 20 Nominal share capital as at December 31 213 Ordinary shares issued and fully paid Issued on April 3, 2017 for private placement financing round 5,042,017 Issued on April 26, 2017 for conversion of loan note 1,221,361 Issued on October 28, 2017 for acquisition of license 490,798 At December 31, 2017 71,094,974 Nominal value at December 31, 2017 (£) 0.003 Issued capital at December 31, 2017 (£) 213,285 Ordinary share capital 2018 Balance at beginning of year 213 Issuances in the year 1 Nominal share capital as at December 31 214 Ordinary shares issued and fully paid At January 1, 2018 71,094,974 Issued on June 1, 2018 for public offering 50,076 Issued on August 3, 2018 for exercise of share options 10,000 Issued on October 22, 2018 for exercise of share options 85,222 At December 31, 2018 71,240,272 Nominal value at December 31, 2018 (£) 0.003 Issued capital at December 31, 2018 (£) 213,721 Ordinary share capital 2019 Balance at beginning of year 214 Issuances in the year 80 Nominal share capital as at December 31 294 Ordinary shares issued and fully paid At January 1, 2019 71,240,272 Issued on April 23, 2019 for OncoMed acquisition 24,783,320 Issued on June 21, 2019 for conversion of loan note 1,936,030 At December 31, 2019 97,959,622 Nominal value at December 31, 2019 (£) 0.003 Issued capital at December 31, 2019 (£) 293,879
Summary of Share Premium	December 31, Share premium 2017 At January 1, 2017 99,975 Issued on April 3, 2017 for private placement financing round 14,985 Issued on April 26, 2017 for conversion of loan note 2,478 Issued on October 28, 2017 for acquisition of license 1,519 Transaction costs for issued share capital (730 ) At December 31, 2017 118,227 December 31, Share premium 2018 At January 1, 2018 118,227 Issued on June 1, 2018 for public offering 150 Issued on August 3, 2018 for exercise of share options 13 Issued on October 22, 2018 for exercise of share options 110 Transaction costs for issued share capital (8 ) At December 31, 2018 118,492 December 31, Share premium 2019 At January 1, 2019 118,492 Issued on June 21, 2019 for conversion of loan note 3,953 Transaction costs for issued share capital (761 ) At December 31, 201 9 121,684
Summary of Other Capital Reserves	Other capital reserves Shares to be issued Share-based payments Equity component of convertible loan Total At January 1, 2017 2,673 9,476 517 12,666 Share-based payments expense during the year — 4,983 — 4,983 Shares issued (1,083 ) — — (1,083 ) Equity component of convertible loan instrument — — (207 ) (207 ) At December 31, 2017 1,590 14,459 310 16,359 Shares to be issued Share-based payments Equity component of convertible loan Warrants issued Total At January 1, 2018 1,590 14,459 310 — 16,359 Share-based payments expense during the year — 2,302 — — 2,302 Share-based payments release for exercise of options — (112 ) — — (112 ) Warrants issued for TAP funding — — — 44 44 At December 31, 2018 1,590 16,649 310 44 18,593 Shares to be issued Share-based payments Equity component of convertible Warrants for TAP Merger Total At January 1, 2019 1,590 16,649 310 44 — 18,593 Acquisition of OncoMed (Note 5) — — — — 40,818 40,818 Shares issued during the year (1,590 ) — — — — (1,590 ) Convertible loan conversion — — (310 ) — — (310 ) Share-based payments expense during the year — 1,636 — — — 1,636 Share-based payments release for exercise of options — — — — — — At December 31, 2019 — 18,285 — 44 40,818 59,147
Summary of Accumulated Loss	Year ended December 31 2017 2018 2019 Other reserves 7,000 7,000 7,000 Accumulated losses (79,316 ) (111,221 ) (146,283 ) Accumulated deficit (72,316 ) (104,221 ) (139,283 )

Interest-bearing loans and bo_2

Interest-bearing loans and borrowings (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Interest-bearing Loans and Borrowings	Year ended December 31 2018 2019 Convertible loan notes (“Novartis Notes”) 2,039 — Bank loan 19,446 20,512 At December 31 21,485 20,512 Current 6,838 15,139 Non-current 14,647 5,373

Provisions (Tables)

Provisions (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Provisions	Year ended December 31 2018 2019 Social security contributions on share options 842 104 Provision for deferred cash consideration 2,131 1,654 At December 31 2,973 1,758 Current 332 309 Non-current 2,641 1,449
Summary of Social Security Contributions on Share Options	Year ended December 31 Social security contributions on share options 2017 2018 2019 At beginning of year 1,172 2,288 842 Arising during the year 1,116 — — Released — (1,446 ) (738 ) At December 31 2,288 842 104 Current — — — Non-current 2,288 842 104
Summary of Provisions for Deferred Cash Consideration	Year ended December 31 Provisions for deferred cash consideration 2017 2018 2019 At beginning of year — 2,061 2,131 Arising during the year 2,061 — — Increase in provision due to the unwinding of the time value of money — 443 221 Decrease in provision due to a change in estimates relating to timelines and probabilities of contractual milestones being achieved (see Note 12) — (373 ) (698 ) At December 31 2,061 2,131 1,654 Current 274 332 309 Non-current 1,787 1,799 1,345

Warrant liability (Tables)

Warrant liability (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Warrant Liability	Year ended December 31 2017 2018 2019 At beginning of year — 1,346 1,006 Issued during the year 1,292 376 131 Movement during the year 54 (716 ) (1,006 ) At December 31 1,346 1,006 131
Summary of Weighted Average Inputs to the Models Used for the Fair Value of Warrants Granted	The following table lists the weighted average inputs to the models used for the fair value of warrants granted during the year ended December 31: Year ended December 31 2018 2019 Expected volatility (%) 65 67 Risk-free interest rate (%) 1.56 1.26 Expected life of share options (years) 10 10.0 Market price of ordinary shares (£) 2.31 0.83 Model used Black Scholes Black Scholes

Other liability (Tables)

Other liability (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Other Liabilities	Year ended December 31 2018 2019 At beginning of year — 34 Interest accretion — 10 Arising during the year 34 — At December 31 34 44

Trade and other payables (Table

Trade and other payables (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Trade and Other Payables	Year ended December 31 2018 2019 Trade payables 4,393 6,148 Social security and other taxes 161 183 Other payables 16 21 At December 31 4,570 6,352

Changes in liabilities arisin_2

Changes in liabilities arising from financing activities (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Changes in Liabilities Arising from Financing Activities	Contingent Lease Bank Novartis Warrant Deferred cash consideration TAP Total Carrying value at January 1, 2018 — — 18,775 1,977 1,346 2,061 — 24,159 Financing cash flows — — (2,111 ) — — — 34 (2,077 ) Changes in fair values — — (375 ) — (716 ) 70 — (1,021 ) Interest expense — — 2,427 185 — — — 2,612 Loss on modification — — 730 — — — — 730 Other — — — (124 ) 375 — — 251 Carrying value December 31, 2018 — — 19,446 2,038 1,005 2,131 34 24,654 Adoption of IFRS 16 (Leases) — 2,534 — — — — — 2,534 Financing cash flows — (2,212 ) (1,739 ) — — — — (3,951 ) Changes in foreign exchange — (131 ) — — — — — (131 ) Changes in fair values 354 — — — (874 ) (477 ) 10 (987 ) Interest expense — 1,314 3,262 20 — — — 4,596 Gain on modification — — (457 ) — — — — (457 ) Issuance of equity — — — (2,058 ) — — — (2,058 ) Acquisition of subsidiary (Note 5) — 10,689 — — — — — 10,689 Lease term reassessment — (290 ) — — — — — (290 ) Carrying value at December 31, 2019 354 11,904 20,512 — 131 1,654 44 34,599

Financial and capital risk ma_2

Financial and capital risk management and fair value measurement (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Fair Value Hierarchy	25.3 Fair value hierarchy Fair value measurement using Date of valuation Total Quoted prices in active markets (Level 1) Significant observable inputs (Level 2) Significant unobservable inputs (Level 3) Liabilities measured at fair value Provision for deferred cash consideration (Note 20) December 31, 2019 1,654 — — 1,654 Provision for contingent consideration (Note 5) December 31, 2019 354 — — 354 Warrant liability (Note 21) December 31, 2019 131 — 131 — Liabilities for which fair values are disclosed Bank loan (Note 19) December 31, 2019 20,512 — 20,512 — There were no transfers between Level 1 and Level 2 during 2019. Fair value measurement hierarchy for liabilities as at December 31, 2018: Fair value measurement using Date of valuation Total Quoted prices in active markets (Level 1) Significant observable inputs (Level 2) Significant unobservable inputs (Level 3) Liabilities measured at fair value Provision for deferred cash consideration (Note 20) December 31, 2018 2,061 — — 2,061 Warrant liability (Note 21) December 31, 2018 1,346 — 1,346 — Liabilities for which fair values are disclosed Convertible loan (Note 19) December 31, 2018 1,977 — 1,977 — Bank loan (Note 19) December 31, 2018 18,775 — 18,775 —
Summary of the Changes in Level 3	The following table presents the changes in level 3 items for the periods ended December 31, 2019 and December 31, 2018: Provision for Provision for January 1, 2018 2,061 — Unwinding of the time value of money recognised as a finance charge 443 — Change in estimate relating to probabilities (revision to intangible asset, see Note 13) (373 ) — December 31, 2018 2,131 — January 1, 2019 2,131 — Unwinding of the time value of money (recognized as a finance charge) 221 — Change in estimate relating to probabilities (revision to intangible asset, see Note 13) (698 ) — Change in estimate relating to probabilities (recognized as an administrative expense) — 354 December 31, 2019 1,654 354
Summary of Changes In Significant Unobservable Inputs Under Valuation Model Used In Level Fair Value Measurement	The significant unobservable inputs used in the fair value measurements categorized within Level 3 of the fair value hierarchy, together with a quantitative sensitivity analysis as at December 31, 2019 and 2018 are as shown below: Valuation Significant unobservable inputs Input r ( average ) Sensitivity of the input to fair value Provision for deferred cash consideration DCF WACC 2019: 15.3% 1% increase would result in a decrease in fair value by £38,000 . WACC 2018: 15.3% 1% decrease would result in an Probability of success 2019: 15.8–95% 10% increase would result in an Probability of success 2018: 28%–95% 10% decrease Contingent consideration liability DCF Ongoing uncertainty in the clinical development of the Navi product. Not applicable Total potential payments future payments relating to the contingent consideration liability on a gross, undiscounted basis are approximately $80.0 million (see Note 30). Regulatory approval and commercialisation risks. Sensitivity of the input to fair value is primarily driven by uncertainty in the clinical development of the Navi product. As at December 31, 2019, we are completing a Phase 1b clinical trial. Future potential payments under the CVR arrangement are contingent on i) future development milestones and ii) future sales of the Navi product, following regulatory approval and commercialisation.
Summary of Maturity Profile of Financial Liabilities Based on Contractual Undiscounted Payments	The table below summarizes the maturity profile of the Group’s financial liabilities based on contractual undiscounted payments at December 31, 2019: Payments due by period Up to 1 year 1–3 years 3–5 years Over 5 years Total Bank loan (Note 19) 17,185 5,484 — — 22,669 Leases (Note 4) 2,634 4,643 4,913 8,105 20,295 Trade and other payables (Note 23) 6,352 — — — 6,352 Contingent consideration liability (Note 5) 354 — — — 354 26,525 10,127 4,913 8,105 49,670
Summary of Contractual Obligations	The table below summarizes the maturity profile of the Group’s financial liabilities based on contractual undiscounted payments at December 31, 2018: Payments due by period Up to 1 year 1–3 years 3–5 years Over 5 years Total Convertible loan (Note 19) 83 2,162 — — 2,245 Bank loan (Note 19) 8,260 15,589 — — 23,849 Leases (Note 27) 332 204 — — 536 Trade and other payables (Note 23) 4,570 — — — 4,570 13,245 17,955 — — 31,200
Detailed Information About Cash And Cash Equivalents By Currency Type	The table below shows analysis of the pound sterling equivalent of period-end Year ended Year ended Cash at bank and in hand: Pound sterling 2,525 23,189 US dollars 13,807 1,809 Swiss francs 11 — Euro 4 44 16,347 25,042
Detailed Onformation About Gain Loss On Foreign Currency Translaction Recognized In Income Statement	The table below shows those transactional exposures that give rise to net currency gains and losses recognized in the consolidated income statement. Such exposures comprise the net monetary assets and monetary liabilities of the Group that are not denominated in the functional currency of the relevant Group entity. As at year end, these exposures were as follows: Year ended Year ended Net foreign currency assets / (liabilities): US dollars (219 ) (542 ) Swiss francs (6 ) — Euro (812 ) (1,430 ) (1,037 ) (1,972 )
Summary of sensitivity analyis of currency movement	The following table details the Group’s sensitivity to a 10% change in the period-end Year ended December 31, 2019 US dollar Euro Net foreign currency assets / (liabilities): Loss before tax 20 74 Equity 20 74 Year ended December 31, 2018 US dollar Euro Net foreign currency assets / (liabilities): Loss before tax 49 130 Equity 49 130

Share-based payments (Tables)

Share-based payments (Tables)	12 Months Ended
	Dec. 31, 2019
Statement [LineItems]
Summary of Share-based Payments Under IFRS 2	The charge for share-based payments under IFRS 2 arises across the following schemes: Year ended December 31, 2017 2018 2019 2019 Equity Incentive Plan — — 635 2019 NED Equity Incentive Plan — — 160 2015 Plan 2,442 806 63 Mereo BioPharma Group plc Share Option Plan 586 1,064 685 Long Term Incentive Plan 299 320 93 Deferred Bonus Share Plan 325 — — 3,652 2,190 1,636
Summary of Number and Movements in Long Term Incentive Plan Options	The expense recognized for employee services received during the year to December 31, 2019 was £0.1 million (2018: £0.3 million). 2017 Number 2018 Number 2019 Number Granted during the year 185,950 — — Cancelled during the year — — — Lapsed during the year — — (241,374 ) Outstanding at December 31 1,151,446 1,151,446 910,072 Exercisable at December 31 — — —
Summary of Weighted Average Inputs to the Models Used for the Fair Value of Share Options Granted	The following tables list the weighted average inputs to the models used for the fair value of share options granted during the year ended December 31, 2019: EIP 2019 grants NED EIP 2019 grants Expected volatility (%) 66 66 Risk-free interest rate (%) 0.95 0.97 Expected life of share options (years) 10 10 Market price of ordinary shares (£) 0.66 0.63 Model used Black Scholes Black Scholes The following tables list the weighted average inputs to the models used for the fair value of share options granted during the year ended December 31, 2018: Share option plan grants Expected volatility (%) 65 – 67 Risk-free interest rate (%) 1.39 – 1.53 Expected life of share options (years) 10 Market price of ordinary shares (£) 2.76 – 3.25 Model used Black Scholes
Summary of Number and Movements in Deferred Bonus Share Plan	The following tables list the weighted average inputs to the models used for the fair value of share options granted during the year ended December 31, 2019: EIP 2019 grants NED EIP 2019 grants Expected volatility (%) 66 66 Risk-free interest rate (%) 0.95 0.97 Expected life of share options (years) 10 10 Market price of ordinary shares (£) 0.66 0.63 Model used Black Scholes Black Scholes
2019 Equity Incentive Plan [member]
Statement [LineItems]
Summary of Number and Weighted Average Exercise Prices (WAEP) of, and Movements in, Options	The following table illustrates the number and weighted average exercise prices (WAEP) of, and movements in, options for the 2019 EIP during the year: 2019 Options Number WAEP $ Outstanding at beginning of the year — — Granted during the year 801,200 4.29 Cancelled during the year 3,150 5.40 Forfeited during the year — — Exercised during the year — — Outstanding at December 31 798,050 4.29 Exercisable at December 31 — —
2019 Non-Executive Director Equity Incentive Plan [member]
Statement [LineItems]
Summary of Number and Weighted Average Exercise Prices (WAEP) of, and Movements in, Options	The following table illustrates the number and weighted average exercise prices (WAEP) of, and movements in, options for the 2019 NED EIP during the year: 2019 Options Number WAEP $ Outstanding at beginning of the year — — Granted during the year 77,000 4.20 Cancelled during the year — — Forfeited during the year — — Exercised during the year — — Outstanding at December 31 77,000 4.20 Exercisable at December 31 38,472 4.40
2015 Plan [member]
Statement [LineItems]
Summary of Number and Weighted Average Exercise Prices (WAEP) of, and Movements in, Options	The following table illustrates the number and weighted average exercise prices (WAEP) of, and movements in, options for the 2015 Plan during the year: 2017 2018 2019 Number WAEP £ Number WAEP Outstanding at beginning of the year 9,198,655 1.32 9,124,610 1.32 8,983,133 1.32 Granted during the year — — — — — — Cancelled during the year — — — — — — Forfeited during the year (74,045 ) 1.29 (46,255 ) 1.29 (59,533 ) 1.29 Exercised during the year — — (95,222 ) 1.29 — — Outstanding at December 31 9,124,610 1.32 8,983,133 1.32 8,923,600 1.32 Exercisable at December 31 5,655,676 1.31 8,007,029 1.31 8,901,478 1.32
Mereo BioPharma Group plc Share Option Plan [member]
Statement [LineItems]
Summary of Number and Weighted Average Exercise Prices (WAEP) of, and Movements in, Options	The following table illustrates the number and weighted average exercise prices (WAEP) of, and movements in, options for the Option Plan during the year: 2017 2018 2019 Number WAEP £ Number WAEP £ Number WAEP £ Outstanding at beginning of the year — — 1,578,188 3.05 1,881,555 3.10 Granted during the year 1,593,188 3.05 388,000 3.14 — — Cancelled during the year — — — — — — Forfeited during the year (15,000 ) 3.03 (84,633 ) 3.03 (357,490 ) 3.21 Outstanding at December 31 1,578,188 3.05 1,881,555 3.10 1,524,065 3.07 Exercisable at December 31 — — — — 40,141 3.03
Long-term incentive plan [member]
Statement [LineItems]
Summary of Weighted Average Inputs to the Models Used for the Fair Value of Share Options Granted	The following tables list the weighted average inputs to the models used for the fair value of LTIP options granted during the years ended December 31, 2017, 2018 and 2019. LTIP Share Price Element Year ended December 31 2017 2018 201 9 Expected volatility (%) 51.7 — — Risk-free interest rate (%) 0.17-0.39 — — Expected life of share options (years) 3-5 — — Market price of ordinary shares (£) 3.03 — — Model used Monte Carlo — — LTIP Strategic Element Year ended December 31 2017 2018 201 9 Expected volatility (%) 51.7 — — Risk-free interest rate (%) 0.39 — — Expected life of share options (years) 5 — — Market price of ordinary shares (£) 3.03 — — Model used Black Scholes — —
Deferred bonus share plan [member]
Statement [LineItems]
Summary of Number and Movements in Deferred Bonus Share Plan	The following table illustrates the number of, and movements in, DBSP options during the year: 2017 Number 2018 Number 2019 Number Outstanding at January 1 62,180 163,000 163,000 Awarded during the year 100,820 — — Granted during the year — — — Outstanding at December 31 163,000 163,000 163,000 Exercisable at December 31 — — —

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary Of Maturity Analysis Of Operating Lease Payments Receivable	The maturity analysis of payments receivable by the Group in its capacity as sublessor is disclosed below: December 31, December 31, Within one year 552 — After one year but not more than five years — — More than five years — — 552 —

Related party disclosures (Tabl

Related party disclosures (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary Of Compensation of key management personnel of the Group	The remuneration of key management personnel of the Group is set out below in aggregate: Year ended December 31, 2017 2018 2019 Short-term benefits 2,757 3,176 3,488 Post-employment benefits 87 60 64 IFRS 2 share-based payment charge 2,726 1,470 1,152 Total compensation paid to key management personnel 5,570 4,706 4,704

Significant Accounting Polici_4

Significant Accounting Policies - Summary of Depreciation Method For Property Plant And Equipment And Useful Life (Detail)	12 Months Ended
	Dec. 31, 2019
Buildings | Bottom of range [member]
Statement [line items]
Useful life of right-of-use asset	6 years
Buildings | Top of range [member]
Statement [line items]
Useful life of right-of-use asset	9 years
Equipment | Bottom of range [member]
Statement [line items]
Useful life of right-of-use asset	1 year
Equipment | Top of range [member]
Statement [line items]
Useful life of right-of-use asset	2 years

Significant Accounting Polici_5

Significant Accounting Policies - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)
Disclosure of voluntary change in accounting policy [line items]
Reclassification of modification loss on bank loan into finance charges	£ 0.7
OncoMed [Member]
Disclosure of voluntary change in accounting policy [line items]
Acquisition of non-current assets	£ 22.4

Significant Accounting Polici_6

Significant Accounting Policies - Summary of Depreciation Calculated on Straight-Line Basis Over Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2019
Leasehold improvements [member]
Disclosure of detailed information about property, plant and equipment [line items]
Estimated useful lives	10 years
Office equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Estimated useful lives	5 years
IT equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Estimated useful lives	3 years

Significant judgments, estima_2

Significant judgments, estimates and assumptions - Additional Information (Detail) £ in Millions, $ in Millions	Dec. 31, 2019GBP (£)	Dec. 31, 2019USD ($)	Apr. 23, 2019
Significant Accounting Judgments Estimates And Assumptions [Abstract]
Fair value of the contingent consideration liability	£ 0.4	$ 0.5
Potential payments under the CVR arrangement		$ 80
Percentage of voting equity interests acquired			100.00%

Changes in accounting policie_2

Changes in accounting policies - Additional information (Detail) - GBP (£) £ in Millions	Jun. 23, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 03, 2020	May 31, 2020	Apr. 23, 2019	Jan. 01, 2019
Statement [line items]
Weighted average incremental borrowing rate							15.00%
Cash outflow for leases		£ 2.2	£ 0.3
Changes in right of use assets		0.3
Subsequent Event [Member]
Statement [line items]
Total cash current				£ 61.5	£ 10.1
Private placement [Member]
Statement [line items]
Net proceeds from issuance of private placement	£ 51.4
Leased Property [Member]
Statement [line items]
Right-of-use asset							£ 1.2
Leased Property [Member] | OncoMed [Member]
Statement [line items]
Right of use assets acquired						£ 10.8
Medical Equipment [Member]
Statement [line items]
Right-of-use asset							£ 1.3
IFRS 16 [Member]
Statement [line items]
Right-of-use asset		£ 2.6
IFRS 16 [Member] | Other operating expenses | straight-line basis
Statement [line items]
Operating lease duration short term leases		12 months

Changes in accounting policie_3

Changes in accounting policies - Summary of adjustments recognized at the date of initial application of IFRS 16 (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Non-current assets
Property, plant and equipment	£ 11,558	£ 149	£ 153	£ 174
Total impact on assets	86,449	67,276
Current liabilities
Trade and other payables	6,352	4,570
Lease liability	2,586
Non-current liabilities
Lease liabilities	9,318
Total impact on liabilities	£ 46,193	34,505
Previously
Non-current assets
Property, plant and equipment		149
Prepayments and other		1,067
Current liabilities
Trade and other payables		4,570
Non-current liabilities
Accruals		4,437
Impact of IFRS 16
Non-current assets
Property, plant and equipment		2,552
Prepayments and other		(50)
Total impact on assets		2,502
Current liabilities
Lease liability		607
Non-current liabilities
Lease liabilities		1,927
Accruals		(32)
Total impact on liabilities		(2,502)
Restated
Non-current assets
Property, plant and equipment		2,701
Prepayments and other		1,017
Current liabilities
Trade and other payables		4,570
Lease liability		607
Non-current liabilities
Lease liabilities		1,927
Accruals		£ 4,405

Changes in accounting policie_4

Changes in accounting policies - Summary of reconciliation from operating lease commitments (Detail) £ in Thousands	Dec. 31, 2018GBP (£)
Statement [line items]
Operating lease commitments	£ 536
Effect of discounting	(944)
Reassessment of lease term under IFRS 16	2,942
IFRS 16
Statement [line items]
Lease liabilities recognised	£ 2,534

Changes in accounting policie_5

Changes in accounting policies - Summary of leases under IFRS 16 (Detail) £ in Thousands	12 Months Ended
	Dec. 31, 2019GBP (£)
Disclosure of voluntary change in accounting policy [abstract]
Depreciation	£ 1,505
Interest expense	1,314
Foreign exchange gain	29
Income from sub-leasing right-of-use assets	£ 855

Changes in accounting policie_6

Changes in accounting policies - Summary of Interest bearing Loans And Borrowings Convertible Loan Notes Explanatory (Detail) £ in Thousands	Dec. 31, 2017GBP (£)
Disclosure of financial liabilities at date of initial application of IFRS 9 [abstract]
At January 1, 2018 (as calculated under IAS 39)	£ 1,977
Amounts restated through retained earnings	(124)
At January 1, 2018 (as calculated under IFRS 9)	£ 1,853

Acquisition of subsidiary - Add

Acquisition of subsidiary - Additional Information (Detail) £ in Thousands, shares in Millions, $ in Millions	Apr. 23, 2019GBP (£)shares	Dec. 31, 2019GBP (£)	Dec. 31, 2019GBP (£)	Dec. 31, 2019USD ($)
Disclosure of detailed information about business combination [line items]
Percentage of voting interest acquired	100.00%
Gain on bargain purchase business combination	£ 3,681
Net income recognized on acquisition			£ 1,000
Maximum undiscounted amount of the Navi milestone | $				$ 80
NAVI milestones [member]
Disclosure of detailed information about business combination [line items]
Navi milestone fair value		£ 400	400	0.5
Maximum undiscounted amount of the Navi milestone | $				$ 80
Unlikely scenario event [member]
Disclosure of detailed information about business combination [line items]
Revenue of combined entity as if combination occurred at the period beginning			3,300
Groups loss for the period			£ 42,900
Unlikely scenario event [member] | NAVI milestones [member]
Disclosure of detailed information about business combination [line items]
Conditions For Additional Consideration			Additional cash consideration becomes payable under a contingent value rights (“CVR”) agreement, if, within eighteen months following the completion date, the Group enters into eligible partnership or investment transactions in relation to OncoMed’s navicixizumab product and, within five years of the completion date, the Group receives certain eligible cash milestone payment (“Navi Milestone”).
OncoMed [Member]
Disclosure of detailed information about business combination [line items]
Percentage of voting interest acquired	100.00%
Gain on bargain purchase business combination	£ 3,700
Acquisition related costs business combination			£ 2,600
Acquiree revenue		0
Acquiree loss for the period		5,700
Cash and deposits acquired	£ 10,100
Incremental transaction costs		£ 800	£ 800
Business acquisition shares issued | shares	24.8
Fair value and a gross contractual value	£ 200

Acquisition of subsidiary - Sum

Acquisition of subsidiary - Summary of Net Assets Acquired (Detail) £ in Thousands	Apr. 23, 2019GBP (£)
Disclosure of detailed information about business combination [abstract]
Cash and short-term deposits	£ 10,074
Short-term investments	29,019
Other receivables	155
Prepayments	1,699
Property, plant and equipment	82
Right-of-use assets	10,755
Identifiable intangible assets	12,693
Other liabilities	(9,215)
Lease liabilities	(10,689)
Net identifiable assets	44,573
Bargain purchase	(3,681)
Total consideration	40,892
Satisfied by:
Equity instruments (24.8 million ordinary shares)	40,892
Contingent consideration	0
Total consideration transferred	£ 40,892

Group Information - Additional

Group Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019
US Mereo MergerCo [Member]
Disclosure of subsidiaries [line items]
Proportion of ownership interest in subsidiary	100.00%

Group Information - Summary of

Group Information - Summary of Information About Subsidiaries of the Group (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Mereo BioPharma 1 Limited [member]
Disclosure of subsidiaries [line items]
Name	Mereo BioPharma 1 Limited
Principal activities	Pharmaceutical R&D
Country of incorporation	U.K.
% equity interest	100.00%	100.00%
Mereo BioPharma 2 Limited [member]
Disclosure of subsidiaries [line items]
Name	Mereo BioPharma 2 Limited
Principal activities	Pharmaceutical R&D
Country of incorporation	U.K.
% equity interest	100.00%	100.00%
Mereo BioPharma 3 Limited [member]
Disclosure of subsidiaries [line items]
Name	Mereo BioPharma 3 Limited
Principal activities	Pharmaceutical R&D
Country of incorporation	U.K.
% equity interest	100.00%	100.00%
Mereo BioPharma 4 Limited [member]
Disclosure of subsidiaries [line items]
Name	Mereo BioPharma 4 Limited
Principal activities	Pharmaceutical R&D
Country of incorporation	U.K.
% equity interest	100.00%	100.00%
Mereo BioPharma Ireland Limited [member]
Disclosure of subsidiaries [line items]
Name	Mereo BioPharma Ireland Limited
Principal activities	Pharmaceutical R&D
Country of incorporation	Ireland
% equity interest	100.00%	100.00%
OncoMed Pharmaceuticals Inc [Member]
Disclosure of subsidiaries [line items]
Name	OncoMed Pharmaceuticals, Inc.
Principal activities	Pharmaceutical R&D
Country of incorporation	U.S.
% equity interest	100.00%
Navi Subsidiary Inc [Member]
Disclosure of subsidiaries [line items]
Name	Navi Subsidiary, Inc.
Principal activities	Pharmaceutical R&D
Country of incorporation	U.S.
% equity interest	100.00%
Mereo US Holdings Inc [member]
Disclosure of subsidiaries [line items]
Name	Mereo US Holdings Inc.
Principal activities	Holding company
Country of incorporation	U.S.
% equity interest	100.00%	100.00%
Mereo MergerCo One Inc [member]
Disclosure of subsidiaries [line items]
Name	Mereo MergerCo One Inc.
Principal activities	Holding company
Country of incorporation	U.S.
% equity interest		100.00%
Mereo BioPharma Group plc Employee Benefit Trust [member]
Disclosure of subsidiaries [line items]
Name	Mereo BioPharma Group plc Employee Benefit Trust
Principal activities	Employee share scheme
Country of incorporation	Jersey

Loss before taxation - Addition

Loss before taxation - Additional Information (Detail) - GBP (£) £ in Thousands	Jan. 01, 2019	Dec. 31, 2019	Dec. 31, 2018
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Depreciation		£ 1,505
Interest expense		£ 1,314
Operating lease expense			£ 293
IFRS 16
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Depreciation	£ 1,500
Interest expense	£ 1,300

Loss before taxation - Summary

Loss before taxation - Summary of information about Loss Before Taxation (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Detailed Information About Loss Before Taxation [Abstract]
Fees payable to the Company's Auditor for the audit of Group accounts	£ 514	£ 323
Fees payable to the Company's Auditor for other services:
Audit of subsidiary accounts	45	30
Audit-related assurance services	311	171
Accounting advisory services		10
Legal and professional fees including patent costs	2,413	936
Operating lease expense (IAS 17)		293
Depreciation of right-of-use assets (IFRS 16)	1,505
Depreciation (excluding right-of-use assets)	£ 52	£ 40

Employees- Additional Informati

Employees- Additional Information (Detail) - Directors	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of employee abstract [Abstract]
Number Of Directors	2	2

Employees- Summary of Average M

Employees- Summary of Average Monthly Persons Employed By Group (Detail) - Number	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
By activity
Average number of employees	46	36
Administrative [member]
By activity
Average number of employees	28	24
Research and development [member]
By activity
Average number of employees	18	12

Employees - Summary of Total co

Employees - Summary of Total compensation cost for persons Employed by the Group (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of employee [line items]
Share-based payment expense	£ 1,636	£ 2,190	£ 3,652
Total employee	8,007	6,198
Research and development expenses [member]
Disclosure of employee [line items]
Salaries	2,824	1,792
Social security costs	110	(30)
Pension contributions	62	73
Share-based payment expense	152	526
Administrative expenses [member]
Disclosure of employee [line items]
Salaries	3,384	2,903
Social security costs	(124)	(828)
Pension contributions	114	99
Share-based payment expense	£ 1,485	£ 1,663

Employee - Summary of Compensat

Employee - Summary of Compensation Cost For Directors (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of employee [line items]
Pension contributions	£ 64	£ 60	£ 87
Total	4,704	4,706	£ 5,570
Directors [member]
Disclosure of employee [line items]
Salaries and fees	1,106	1,047
Benefits in kind	17	15
Pension contributions	25	11
Bonus	294	512
Total	£ 1,442	£ 1,585

Other income _ expenses and a_3

Other income / expenses and adjustments - Summary of Finance Income (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Other Income Expenses And Adjustment [Line Items]
Total finance income	£ 42	£ 307	£ 827
Interest earned on short-term investments	141
Gain on short-term investments	194
Total finance income	£ 377	£ 307	£ 827

Other income _ expenses and a_4

Other income / expenses and adjustments - Summary of Finance Charge (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Other Income Expenses And Adjustment [Line Items]
Interest payable on convertible loan	£ (20)	£ (185)	£ (103)
Interest on TAP funding	(10)
Interest payable on bank loan	(1,739)	(1,645)	(327)
Interest on lease liabilities	(1,314)
Accreted interest on bank loan	(1,523)	(782)	(67)
Transaction costs on bank loan			(200)
Modification (loss)/gain on bank loan	456	(730)
Loss on short-term deposits		(22)	(339)
Discounting of provision for deferred cash consideration	(221)	(443)
Change in warrant fair value	875	716	(54)
Total finance charge	£ (3,496)	£ (3,091)	£ (1,090)

Other income _ expenses and a_5

Other income / expenses and adjustments - Summary of Finance Charge (Parenthetical) (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)
Disclosure of Other Income Expenses And Adjustment [Abstract]
Reclassification of modification loss on bank loan into finance charges	£ 0.7

Income Tax - Summary of Income

Income Tax - Summary of Income Tax Credit (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Major components of tax expense (income) [abstract]
U.K. corporation tax R&D credit	£ 5,149	£ 5,277	£ 8,152
Other tax income / (expense)	1,125
Tax credit for the year	£ 6,274	£ 5,277	£ 8,152

Income Tax - Additional Informa

Income Tax - Additional Information (Detail) - GBP (£) £ in Thousands	Apr. 01, 2020	Dec. 31, 2019	Apr. 01, 2017	Dec. 31, 2019	Dec. 31, 2018
Disclosure of income tax credit [line items]
Description of accumulated tax losses					The deferred tax liability has arisen from the recognition of separately identifiable intangible assets on the acquisition of OncoMed. A deferred tax asset on losses has been recognized up to the level of the deferred tax liability, resulting in a net £nil deferred income tax liability.
Description of corporate tax reduction				A reduction in the rate of UK corporation tax to 19% from April 1, 2017 and to 17% from April 1, 2020 has been substantively enacted.
Deferred tax liability
Other tax income received or receivable		1,100		1,100
Other taxes recoverable		979		979
Deferred Income Tax Liability
Uncertain tax position off balance sheet		£ 2,500		£ 2,500
Uncertain tax position off balance sheet | %		20.00%		20.00%
Indefinitely Expired [Member]
Disclosure of income tax credit [line items]
Tax Losses carry forward				£ 40,900
UK Tax Authority [Member]
Disclosure of income tax credit [line items]
Corporate tax reduction	19.00%		19.00%
Standard rate of corporation tax applied to reported loss				19.00%	19.00%
Rate at which deferred tax assets and liabilities would be recognized					17.00%
Tax Losses carry forward				£ 70,200	£ 50,000
US Tax Authority [Member]
Disclosure of income tax credit [line items]
Corporate tax reduction					21.00%
Rate at which deferred tax assets and liabilities would be recognized		21.00%
Tax Losses carry forward				47,500
US Tax Authority [Member] | Expire In 2023 [Member]
Disclosure of income tax credit [line items]
Tax Losses carry forward				£ 6,600
Expiration date				2023
US Tax Authority [Member] | Expire In 2028 [Member]
Disclosure of income tax credit [line items]
Tax Losses carry forward				£ 3,200
Expiration date				2028
Changes in tax rates or tax laws enacted or announced [member] | UK Tax Authority [Member]
Disclosure of income tax credit [line items]
Corporate tax reduction	17.00%

Income Tax - Summary of Reconci

Income Tax - Summary of Reconciliation to the Earnings Loss Per Income Statement (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Major components of tax expense (income) [abstract]
Loss on ordinary activities before income tax	£ (41,118)	£ (37,306)	£ (46,951)
Loss on ordinary activities before tax at the U.K.'s statutory income tax rate of 19% (2018: 19%)	7,812	7,088	9,038
Expenses not deductible for income tax purposes (permanent differences)	(317)	(1,070)	(13)
Temporary timing differences	(343)	(277)	(712)
R&D relief uplift	2,540	2,271	3,447
Losses (unrecognized)	(4,380)	(2,804)	(3,785)
Deferred income from MBG loan guarantee costs	(54)	69	177
Differences in overseas tax rates	340
Gain on bargain purchase	699
Other	(23)
Tax credit for the year	£ 6,274	£ 5,277	£ 8,152

Income Tax - Summary of Recon_2

Income Tax - Summary of Reconciliation to the Earnings Loss Per Income Statement (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
UK Tax Authority [Member]
Disclosure Of Income Tax Credit [line items]
Statutory income tax rate	19.00%	19.00%

Income Tax - Summary of Deferre

Income Tax - Summary of Deferred Tax (Detail) - GBP (£)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset (unrecognised)	£ 31,028	£ 9,105	£ 8,388
Losses [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset (unrecognised)	19,443	8,604	6,121
US Tax Credit [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset (unrecognised)	10,032
Accruals [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset (unrecognised)	947
Fixed assets [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset (unrecognised)	400
Other [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset (unrecognised)	202	6
Temporary differences trading [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset (unrecognised)	£ 4	£ 495	£ 2,267

Income tax - Summary of analysi

Income tax - Summary of analysis of recognized deferred tax (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Analysis Of Recognized Deferred Tax [Line Items]
Deferred tax asset/(liabilities)	£ (31,028)	£ (9,105)	£ (8,388)
Acquisition of subsidiary	(2,686)
Recognized in income	2,686
Intangible Asset [member]
Disclosure Of Analysis Of Recognized Deferred Tax [Line Items]
Deferred tax asset/(liabilities)	(2,686)
Acquisition of subsidiary	(2,686)
Net Operating Losses [member]
Disclosure Of Analysis Of Recognized Deferred Tax [Line Items]
Deferred tax asset/(liabilities)	2,686
Recognized in income	£ 2,686

Loss per share - Summary of Los

Loss per share - Summary of Loss Per Share (Detail) - GBP (£) £ / shares in Units, £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings per share [abstract]
Loss	£ (34,844)	£ (32,029)	£ (38,799)
Weighted shares number	89,424,476	71,144,786	69,012,348
Loss per share	£ (0.39)	£ (0.45)	£ (0.56)

Loss per share - Additional inf

Loss per share - Additional information (Detail) - shares	Jun. 21, 2019	Apr. 26, 2017	Dec. 31, 2019	Dec. 31, 2018
Earnings per share [abstract]
Equity shares to be issued			0	864,988
New ordinary shares payable			1,349,692
Warrants issued	1,071,042	632,829	321,444	41,286

Property, plant and equipment -

Property, plant and equipment - Additional information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)
OncoMed Pharmaceuticals, Inc.[member]
Disclosure of detailed information about property, plant and equipment [line items]
Acquisition of right of use assets relates to property lease	£ 10.8
IFRS 16
Disclosure of detailed information about property, plant and equipment [line items]
Right-of-use asset	£ 2.6

Property, Plant and Equipment_2

Property, Plant and Equipment - Summary of IFRS 16 Lease Explanatory (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	£ 149	£ 153	£ 174
Ending balance	11,558	149	153
Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	266	233	218
Additions	21	35	15
Transition to IFRS 16 (Leases)	2,551
Acquisition of subsidiary (Note 5)	10,837
Disposals	(18)	(2)
Adjustment to carrying value	(290)
Currency translation effects	(115)
Ending balance	13,252	266	233
Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	(117)	(80)
Disposals		2	(44)
Depreciation for the year	(1,577)	(39)	(36)
Ending balance	(1,694)	(117)	(80)
Leasehold improvements [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	111	118	134
Ending balance	95	111	118
Leasehold improvements [member] | Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	164	155	155
Additions		9
Acquisition of subsidiary (Note 5)	0
Ending balance	164	164	155
Leasehold improvements [member] | Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	(53)	(37)
Disposals			(21)
Depreciation for the year	(16)	(16)	(16)
Ending balance	(69)	(53)	(37)
Office equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	15	20	15
Ending balance	41	15	20
Office equipment [member] | Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	31	30	20
Additions		1	10
Acquisition of subsidiary (Note 5)	58
Disposals	(18)
Ending balance	71	31	30
Office equipment [member] | Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	(16)	(10)
Disposals			(5)
Depreciation for the year	(14)	(6)	(5)
Ending balance	(30)	(16)	(10)
IT equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	23	15	25
Ending balance	26	23	15
IT equipment [member] | Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	71	48	43
Additions	21	25	5
Acquisition of subsidiary (Note 5)	24
Disposals		(2)
Ending balance	116	71	48
IT equipment [member] | Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	(48)	(33)
Disposals		2	(18)
Depreciation for the year	(42)	(17)	(15)
Ending balance	(90)	£ (48)	£ (33)
Right-of-use asset (building) [member]
Disclosure of detailed information about property, plant and equipment [line items]
Ending balance	10,881
Right-of-use asset (building) [member] | Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Transition to IFRS 16 (Leases)	1,237
Acquisition of subsidiary (Note 5)	10,755
Currency translation effects	(115)
Ending balance	11,877
Right-of-use asset (building) [member] | Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Depreciation for the year	(996)
Ending balance	(996)
Right-of-use asset (equipment) [member]
Disclosure of detailed information about property, plant and equipment [line items]
Ending balance	515
Right-of-use asset (equipment) [member] | Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Transition to IFRS 16 (Leases)	1,314
Acquisition of subsidiary (Note 5)	0
Adjustment to carrying value	(290)
Ending balance	1,024
Right-of-use asset (equipment) [member] | Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Depreciation for the year	(509)
Ending balance	£ (509)

Intangible Assets - Summary of

Intangible Assets - Summary of Detailed Information about Intangible Assets (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about intangible assets [line items]
Beginning balance	£ 32,632	£ 33,005	£ 25,813
Ending balance	44,456	32,632	33,005
Cost or valuation member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	33,005	33,005	25,813
Acquisition of subsidiary	12,693
Currency translation effects	(171)
Ending balance	45,527	33,005	33,005
Depreciation/Amortization and impairment [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	(373)
Revision to estimated value	(698)	(373)
Amortisation and impairment	£ (1,071)		£ (373)
Ending balance		£ (373)

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - GBP (£) £ in Millions	Apr. 23, 2019	Oct. 28, 2017	Dec. 31, 2019	Dec. 31, 2018
OncoMed [Member]
Disclosure of detailed information about intangible assets [line items]
Acquisition of Intangible Assets Other Than Goodwill	£ 12.7
MPH-966 [member]
Disclosure of detailed information about intangible assets [line items]
Deferred equity consideration		£ 7.2
Present value of provision for deferred cash consideration			£ 0.7	£ 0.4

Impairment Testing of Acquire_3

Impairment Testing of Acquired Development Programs Not Yet Available for Use - Summary of Carrying Amount of Acquired Development Programs (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	£ 44,456	£ 32,632
Navicixizumab [Member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	12,522
BPS-804 [member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	11,616	11,616
MPH-966 [member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	6,121	6,819
BGS-649 [member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	9,886	9,886
BCT-197 [member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	£ 4,311	£ 4,311

Impairment Testing of Acquire_4

Impairment Testing of Acquired Development Programs Not Yet Available for Use - Additional Information (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of quantitative information about right-of-use assets [abstract]
Impairment of the acquired products' rights	£ 0
Cash flow projections - Industry-standard asset life	P20Y
Discount rates	15.30%	15.30%

Other Receivables - Summary of

Other Receivables - Summary of Other Receivables (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Disclosure of other receivables [abstract]
Rent deposit	£ 293	£ 293
VAT recoverable	269	316
Other receivables	10
Total	£ 572	£ 609

Cash and Short-term Deposits -

Cash and Short-term Deposits - Summary of Cash and Short-term Deposits (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and cash equivalents [abstract]
Cash at banks and on hand	£ 15,803	£ 5,344
Short-term deposits	544	19,698
Total	£ 16,347	£ 25,042	£ 50,045	£ 53,578

Short-term Investments - Summar

Short-term Investments - Summary of Short-term Investments (Detail) £ in Thousands	Dec. 31, 2018GBP (£)
Short- Term Investments [abstract]
Short-term investments	£ 2,500

Issued Capital and Reserves - S

Issued Capital and Reserves - Summary of Detailed Information of Ordinary Share Capital (Detail) - GBP (£) £ / shares in Units, £ in Thousands	Jun. 21, 2019	Oct. 22, 2018	Aug. 03, 2018	Jun. 01, 2018	Oct. 28, 2017	Apr. 26, 2017	Apr. 03, 2017	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 23, 2019	Oct. 31, 2017
Disclosure of classes of share capital [line items]
Beginning balance									£ 32,771	£ 62,483	£ 79,255
Issuances in the period									2,369		15,000
Ending balance									40,256	32,771	62,483
Nominal value	£ 0.003					£ 0.003
OncoMed [Member]
Disclosure of classes of share capital [line items]
Issued								24,783,320
Ordinary shares [member]
Disclosure of classes of share capital [line items]
Beginning balance									214	213	193
Issuances in the period									80	1	20
Ending balance									£ 294	£ 214	£ 213
Ordinary shares issued and fully paid, Beginning balance									71,240,272	71,094,974
Ordinary shares issued and fully paid, Ending balance									97,959,622	71,240,272	71,094,974
Nominal value		£ 0.003	£ 0.003	£ 0.003			£ 0.003		£ 0.003	£ 0.003	£ 0.003		£ 0.003
Ordinary shares [member] | OncoMed [Member]
Disclosure of classes of share capital [line items]
Nominal value												£ 0.003
Ordinary shares [member] | Private Placement financing round member [Member]
Disclosure of classes of share capital [line items]
Issued							5,042,017
Ordinary shares [member] | Conversion of loan note [member]
Disclosure of classes of share capital [line items]
Issued						1,221,361
Ordinary shares [member] | acquisition of license [member]
Disclosure of classes of share capital [line items]
Issued					490,798
Ordinary shares issued and fully paid, Beginning balance										71,094,974
Ordinary shares issued and fully paid, Ending balance											71,094,974
Ordinary shares [member] | Public Offering [member]
Disclosure of classes of share capital [line items]
Issued				50,076
Ordinary shares [member] | Exercise of share options [member]
Disclosure of classes of share capital [line items]
Issued		85,222	10,000
Ordinary share capital [Member]
Disclosure of classes of share capital [line items]
Beginning balance									£ 213,721	£ 213,285
Ending balance									£ 293,879	£ 213,721	£ 213,285
Issued	1,936,030

Issued Capital and Reserves - A

Issued Capital and Reserves - Additional Information (Detail) - GBP (£) £ / shares in Units, £ in Thousands	Jun. 21, 2019	Apr. 23, 2019	Jan. 01, 2019	Jun. 01, 2018	Apr. 26, 2017	Apr. 03, 2017	Mar. 21, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Oct. 22, 2018	Aug. 03, 2018	Oct. 31, 2017
Disclosure of classes of share capital [line items]
Nominal value	£ 0.003				£ 0.003
Conversion of loan notes into ordinary shares amount	£ 2,400				£ 1,398,552
Conversion of loan notes into ordinary shares	1,071,042				632,829			321,444	41,286
Share conversion price per share	£ 2.21				£ 2.21
Bonus shares received	864,988				588,532
Equity component of convertible loan instrument										£ 62
Equity component (consideration received for the warrants)								£ 44,156	£ 0
Fair value of Acquisition for Ordinary shares		£ 40,892
Nominal value of issued capital								294	£ 214
Equity component of convertible loan [member]
Disclosure of classes of share capital [line items]
Equity component of convertible loan instrument								£ 0
Directors [member]
Disclosure of classes of share capital [line items]
Reduction in share premium							£ 7,000
Novartis [member]
Disclosure of classes of share capital [line items]
Conversion of loan notes into ordinary shares amount	£ 2,400
Ordinary shares [member]
Disclosure of classes of share capital [line items]
Ordinary shares issued and allotted		24,783,320		50,076		5,042,017					85,222	10,000	490,798
Nominal value				£ 0.003		£ 0.003		£ 0.003	£ 0.003	£ 0.003	£ 0.003	£ 0.003	£ 0.003
Ordinary shares price per share				£ 3		£ 2.975
Cash consideration				£ 150,228		£ 15,000,000
Shares issued as fully paid up								97,959,622	71,240,272	71,094,974
Ordinary shares [member] | OncoMed [Member]
Disclosure of classes of share capital [line items]
Nominal value		£ 0.003
Ordinary shares price per share		£ 1.65
Fair value of Acquisition for Ordinary shares								£ 40,900
Ordinary shares [member] | OncoMed [Member] | Issued capital [member]
Disclosure of classes of share capital [line items]
Nominal value of issued capital								£ 100
Ordinary shares [member] | Novartis [member]
Disclosure of classes of share capital [line items]
Maximum shares to be issued	864,988
Ordinary shares to be issued price per share			£ 1.84
Novartis bonus shares [member]
Disclosure of classes of share capital [line items]
Maximum shares to be issued			864,988
Merger reserve [member] | OncoMed [Member]
Disclosure of classes of share capital [line items]
Shares issued as fully paid up								24,783,320
Merger reserve [member] | OncoMed [Member] | Issued capital [member]
Disclosure of classes of share capital [line items]
Excess Amount Within Other Capital Reserves								£ 40,800

Issued Capital and Reserves -_2

Issued Capital and Reserves - Summary of Share Premium (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of classes of share capital [line items]
Beginning balance	£ 118,492
Ending balance	121,684	£ 118,492
Share premium [member]
Disclosure of classes of share capital [line items]
Beginning balance	118,492	118,227	£ 99,975
Issued on April 3, 2017 for private placement financing round			14,985
Issued on June 1, 2018 for public offering		150
Issued on April 26, 2017 for conversion of loan note			2,478
Issued on October 28, 2017 for acquisition of license			1,519
Transaction costs for issued share capital	(761)	(8)	(730)
Ending balance	121,684	118,492	£ 118,227
Share premium [member] | Share premium issued on August 3, 2018 [member]
Disclosure of classes of share capital [line items]
Issued on August 3, 2018 for exercise of share options		13
Share premium [member] | Share premium issued on October 22, 2018 [member]
Disclosure of classes of share capital [line items]
Issued on August 3, 2018 for exercise of share options		£ 110
Share premium [member] | Share premium issued on June 21, 2019 [member]
Disclosure of classes of share capital [line items]
Issued on April 26, 2017 for conversion of loan note	£ 3,953

Issued Capital and Reserves -_3

Issued Capital and Reserves - Summary of Other Capital Reserves (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of classes of share capital [line items]
Beginning balance	£ 7,000	£ 7,000
Shares issued	2,369		£ 15,000
Equity component of convertible loan instrument			62
Ending balance	7,000	7,000	7,000
Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	18,593	16,359	12,666
Acquisition of OncoMed (Note 5)	40,818
Share-based payments expense during the year	1,636	2,302	4,983
Share-based payments release for exercise of options		(112)
Shares issued	(1,590)		(1,083)
Warrants issued for TAP funding		44
Equity component of convertible loan instrument	(310)		(207)
Ending balance	59,147	18,593	16,359
Shares to be issued [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	1,590	1,590	2,673
Shares issued	(1,590)		(1,083)
Ending balance		1,590	1,590
Share-based payments [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	16,649	14,459	9,476
Share-based payments expense during the year	1,636	2,302	4,983
Share-based payments release for exercise of options		(112)
Ending balance	18,285	16,649	14,459
Equity component of convertible loan [member]
Disclosure of classes of share capital [line items]
Equity component of convertible loan instrument	0
Equity component of convertible loan [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	310	310	517
Equity component of convertible loan instrument	(310)		(207)
Ending balance		310	£ 310
Warrants issued for TAP funding [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	44
Warrants issued for TAP funding		44
Ending balance	44	£ 44
Merger reserve [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Acquisition of OncoMed (Note 5)	40,818
Ending balance	£ 40,818

Issued Capital and Reserves -_4

Issued Capital and Reserves - Summary of Accumulated Loss (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of classes of share capital [abstract]
Other reserves	£ 7,000	£ 7,000	£ 7,000
Accumulated losses	(146,065)	(111,221)	(79,316)
Accumulated deficit	£ (139,065)	£ (104,221)	£ (72,316)

Interest-bearing Loans and Bo_3

Interest-bearing Loans and Borrowings - Summary of Interest-bearing Loans and Borrowings (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about borrowings [abstract]
Convertible loan notes ("Novartis Notes")		£ 2,039
Bank loan	£ 20,512	19,446
Interest-bearing loans and borrowings	20,512	21,485
Current	15,139	6,838
Non-current	£ 5,373	£ 14,647

Interest-bearing Loans and Bo_4

Interest-bearing Loans and Borrowings - Additional Information (Detail) £ / shares in Units, £ in Thousands	Jun. 21, 2019GBP (£)shares	May 03, 2019GBP (£)£ / sharesshares	May 01, 2019GBP (£)	Dec. 31, 2019GBP (£)Installment	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)	Jun. 21, 2019$ / shares
Disclosure of detailed information about borrowings [line items]
Accreted interest on bank loan				£ 1,523	£ 782	£ 67
Carrying value of the loan				£ 20,512	21,485
Bank loan [member]
Disclosure of detailed information about borrowings [line items]
Number of monthly installments | Installment				23
Loan maturity date				March 1, 2021
Interest rate on loans				8.50%
Principal amount				£ 20,500
Number of additional warrants | shares		321,444
Fair value of additional warrants		£ 100
Original Discount Rate			18.00%
Ordinary shares exercise price | £ / shares		£ 2.95
Carrying value of the loan			£ 19,900
Increase decrease through previous and revised borrowings			500
Losses on borrowings recognized in profit and loss			£ 700
Novartis [member]
Disclosure of detailed information about borrowings [line items]
Convertible loan amount	£ 2,400				2,000
Number of converted loans converted to ordinary shares | shares	1,071,042
Conversion price per share | $ / shares							$ 2.21
Reduction in interest-bearing loans and borrowings	£ 2,000
Reduction in other capital reserves	£ 300
Bonus shares | shares	864,988
Notes issued value					£ 2,900
Discounted debt ratio percentage					10.00%
Equity component of the Notes					£ 300

Provisions - Summary of Provisi

Provisions - Summary of Provisions (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure provisions [line items]
Provisions	£ 1,758	£ 2,973
Current	309	332
Non-current	1,449	2,641
Social security contributions on share options [member]
Disclosure provisions [line items]
Provisions	104	842	£ 2,288	£ 1,172
Non-current	104	842	2,288
Provision for deferred cash consideration [member]
Disclosure provisions [line items]
Provisions	1,654	2,131	2,061
Current	309	332	274
Non-current	£ 1,345	£ 1,799	£ 1,787

Provisions - Summary of Social

Provisions - Summary of Social Security Contributions on Share Options (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of other provisions [line items]
Beginning balance	£ 2,973
Ending balance	1,758	£ 2,973
Non-current	1,449	2,641
Social security contributions on share options [member]
Disclosure of other provisions [line items]
Beginning balance	842	2,288	£ 1,172
Arising during the year			1,116
Released	(738)	(1,446)
Ending balance	104	842	2,288
Non-current	£ 104	£ 842	£ 2,288

Provisions - Summary of Provi_2

Provisions - Summary of Provisions for Deferred Cash Consideration (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of other provisions [line items]
Beginning balance	£ 2,973
Ending balance	1,758	£ 2,973
Current	309	332
Non-current	1,449	2,641
Provision for deferred cash consideration [member]
Disclosure of other provisions [line items]
Beginning balance	2,131	2,061
Arising during the year			£ 2,061
Increase in provision due to the unwinding of the time value of money	221	443
Decrease in provision due to a change in estimates relating to timelines and probabilities of contractual milestones being achieved (see Note 12)	(698)	(373)
Ending balance	1,654	2,131	2,061
Current	309	332	274
Non-current	£ 1,345	£ 1,799	£ 1,787

Warrant Liability - Summary of

Warrant Liability - Summary of Warrant Liability (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Warrant Liability [Abstract]
Beginning balance	£ 1,006	£ 1,346
Issued during the year	131	376	£ 1,292
Movement during the year	(1,006)	(716)	54
Ending balance	£ 131	£ 1,006	£ 1,346

Warrant Liability - Additional

Warrant Liability - Additional Information (Detail) - GBP (£) £ / shares in Units, £ in Thousands	May 03, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of classes of share capital [line items]
Percentage of ordinary share capital		1.27%
Fair value of additional warrants grant date	£ 100
Movement during the year		£ (1,006)	£ (716)	£ 54
Warrant [Member]
Disclosure of classes of share capital [line items]
Warrants issued			922,464
Number of warrants outstanding		1,243,908
Warrant [Member] | Bottom of range [member]
Disclosure of classes of share capital [line items]
Exercise price			£ 2.31
Warrant [Member] | Top of range [member]
Disclosure of classes of share capital [line items]
Exercise price			£ 3.30
Warrants Issued on May 3, 2019 [member]
Disclosure of classes of share capital [line items]
Warrants issued	321,444
Exercise price	£ 2.95

Warrant Liability - Summary o_2

Warrant Liability - Summary of Weighted Average Inputs to the Models Used for the Fair Value of Warrants Granted (Detail) - Warrant liability [member] - £ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of classes of share capital [line items]
Expected volatility	67.00%	65.00%
Risk-free interest rate	1.26%	1.56%
Expected life of share options (years)	10 years	10 years
Market price of ordinary shares	£ 0.83	£ 2.31
Model used	Black Scholes	Black Scholes

Other Liability - Summary of Ot

Other Liability - Summary of Other Liabilities (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Other Liabilities [abstract]
Beginning balance	£ 34
Interest accretion	10
Arising during the year		£ 34
Ending balance	£ 44	£ 34

Other Liability - Additional In

Other Liability - Additional Information (Detail)	Nov. 16, 2018GBP (£)	Dec. 31, 2018GBP (£)	Nov. 16, 2018USD ($)	Oct. 08, 2018USD ($)
Disclosure Of Other Liabilities [line items]
Payments receivable from TAP agreement	£ 78,445		$ 100,000
Fair value of liability	£ 34,289
Non cash interest charge	25.80%
Fair value of warrants issued	£ 44,156	£ 44,000
MPH-966 [member]
Disclosure Of Other Liabilities [line items]
Payments receivable from TAP agreement | $				$ 400,000

Trade and Other Payables - Summ

Trade and Other Payables - Summary of Trade and Other Payables (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Trade and other payables [abstract]
Trade payables	£ 6,148	£ 4,393
Social security and other taxes	183	161
Other payables	21	16
At December 31	£ 6,352	£ 4,570

Changes in Liabilities Arisin_3

Changes in Liabilities Arising from Financing Activities - Summary of Changes in Liabilities Arising from Financing Activities (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	£ 24,654	£ 24,159
Financing cash flows	(3,951)	(2,077)
Changes in foreign exchange	(131)
Changes in fair values	(987)	(1,021)
Interest expense	4,596	2,612
Loss on modification		730
Other		251
Adoption of IFRS 16 (Leases)	2,534
Gain on modification	(457)
Issuance of equity	(2,058)
Acquisition of subsidiary (Note 5)	10,689
Lease term reassessment	(290)
Ending balance	34,599	24,654
Contingent consideration [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Changes in fair values	354
Ending balance	354
Lease liability [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Financing cash flows	(2,212)
Changes in foreign exchange	(131)
Interest expense	1,314
Adoption of IFRS 16 (Leases)	2,534
Acquisition of subsidiary (Note 5)	10,689
Lease term reassessment	(290)
Ending balance	11,904
Bank loan [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	19,446	18,775
Financing cash flows	(1,739)	(2,111)
Changes in fair values		(375)
Interest expense	3,262	2,427
Loss on modification		730
Gain on modification	(457)
Ending balance	20,512	19,446
Novartis notes [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	2,038	1,977
Interest expense	20	185
Other		(124)
Issuance of equity	(2,058)
Ending balance		2,038
Warrant liability [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	1,005	1,346
Changes in fair values	(874)	(716)
Other		375
Ending balance	131	1,005
Deferred cash consideration [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	2,131	2,061
Changes in fair values	(477)	70
Ending balance	1,654	2,131
TAP agreement [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	34
Financing cash flows		34
Changes in fair values	10
Issuance of equity	0
Ending balance	£ 44	£ 34

Financial and Capital Risk Ma_3

Financial and Capital Risk Management and Fair Value Measurement - Additional Information (Detail) £ in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)	Dec. 31, 2019USD ($)	Apr. 23, 2019GBP (£)
Disclosure of detailed information about financial instruments [line items]
Fair value of the contingent consideration liability	£ 400	$ 0.5
Potential payments under the CVR arrangement | $		$ 80
Short-term investments acquired			£ 29,019
Short-term investments at carrying value	£ 0
Percentage of increase decrease in sensitivity analysis affecting input to fair value	10.00%
Financial assets at fair value through other comprehensive income, category [member] | OncoMed [Member]
Disclosure of detailed information about financial instruments [line items]
Short-term investments acquired			£ 29,000
Credit risk [member] | Investment counterparties [member]
Disclosure of detailed information about financial instruments [line items]
Maximum exposure to credit risk with one counterparty	£ 10,000
Credit risk [member] | Cash deposit counterparties [member]
Disclosure of detailed information about financial instruments [line items]
Maximum exposure to credit risk with deposit counterparty	£ 5,000

Financial and Capital Risk Ma_4

Financial and Capital Risk Management and Fair Value Measurement - Summary of Fair Value Hierarchy (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Provision for deferred cash consideration [member]
Disclosure of fair value measurement of liabilities [line items]
Date of valuation	Dec. 31, 2019	Dec. 31, 2018
Financial liabilities at fair value	£ 1,654	£ 2,061
Provision for contingent consideration [member]
Disclosure of fair value measurement of liabilities [line items]
Date of valuation	Dec. 31, 2019
Financial liabilities at fair value	£ 354
Warrant liability [member]
Disclosure of fair value measurement of liabilities [line items]
Date of valuation		Dec. 31, 2018
Financial liabilities at fair value		£ 1,346
Warrant liability [member] | Not measured at fair value in statement of financial position but for which fair value is disclosed [member]
Disclosure of fair value measurement of liabilities [line items]
Date of valuation	Dec. 31, 2019
Financial liabilities at fair value	£ 131
Convertible loan [member] | Not measured at fair value in statement of financial position but for which fair value is disclosed [member]
Disclosure of fair value measurement of liabilities [line items]
Date of valuation		Dec. 31, 2018
Financial liabilities		£ 1,977
Bank loan [member] | Not measured at fair value in statement of financial position but for which fair value is disclosed [member]
Disclosure of fair value measurement of liabilities [line items]
Date of valuation	Dec. 31, 2019	Dec. 31, 2018
Financial liabilities	£ 20,512	£ 18,775
Significant observable inputs (Level 2) | Warrant liability [member]
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities at fair value		1,346
Significant observable inputs (Level 2) | Warrant liability [member] | Not measured at fair value in statement of financial position but for which fair value is disclosed [member]
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities at fair value	131
Significant observable inputs (Level 2) | Convertible loan [member] | Not measured at fair value in statement of financial position but for which fair value is disclosed [member]
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities		1,977
Significant observable inputs (Level 2) | Bank loan [member] | Not measured at fair value in statement of financial position but for which fair value is disclosed [member]
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities	20,512	18,775
Significant unobservable inputs (Level 3) | Provision for deferred cash consideration [member]
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities at fair value	1,654	£ 2,061
Significant unobservable inputs (Level 3) | Provision for contingent consideration [member]
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities at fair value	£ 354

Financial and Capital Risk Ma_5

Financial and Capital Risk Management and Fair Value Measurement - Summary of changes in level 3 of fair value of hierarchy (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Summary of changes in level 3 of fair value of hierarchy [Line Items]
Beginning balance	£ 2,973
Ending balance	1,758	£ 2,973
Provision for deferred cash consideration [member]
Summary of changes in level 3 of fair value of hierarchy [Line Items]
Beginning balance	2,131	2,061
Unwinding of the time value of money recognised as a finance charge	221	443
Change in estimate relating to probabilities (revision to intangible asset	698	373
Ending balance	1,654	2,131
Provision for deferred cash consideration [member] | Level 3 of fair value hierarchy [member]
Summary of changes in level 3 of fair value of hierarchy [Line Items]
Beginning balance	2,131	2,061
Unwinding of the time value of money recognised as a finance charge	221	443
Change in estimate relating to probabilities (revision to intangible asset	(698)	(373)
Change in estimate relating to probabilities (recognized as an administrative expense)	0
Ending balance	1,654	£ 2,131
Provision for contingent consideration [member] | Level 3 of fair value hierarchy [member]
Summary of changes in level 3 of fair value of hierarchy [Line Items]
Change in estimate relating to probabilities (recognized as an administrative expense)	354
Ending balance	£ 354

Financial and Capital Risk Ma_6

Financial and Capital Risk Management and Fair Value Measurement - Summary of Changes In Significant Unobservable Inputs Under Valuation Model Used In Level Fair Value Measurement (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Undiscounted contingent liability for future payments	£ 80,000
Weighted average cost of capital [member] | Provision for deferred cash consideration [member] | Discounted cash flow model [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Weighted average cost of capital	15.30%	15.30%
Percentage of increase decrease in sensitivity analysis affecting input to fair value	1.00%	1.00%
Increase decrease in sensitivity analysis affecting input to fair value	£ 38,000	£ 18,000
Probability of success [member] | Provision for deferred cash consideration [member] | Discounted cash flow model [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Percentage of increase decrease in sensitivity analysis affecting input to fair value	10.00%	10.00%
Increase decrease in sensitivity analysis affecting input to fair value	£ 400	£ 900
Bottom of range [member] | Probability of success [member] | Provision for deferred cash consideration [member] | Discounted cash flow model [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Probability of success	15.80%	28.00%
Top of range [member] | Probability of success [member] | Provision for deferred cash consideration [member] | Discounted cash flow model [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Probability of success	95.00%	95.00%

Financial and Capital Risk Ma_7

Financial and Capital Risk Management and Fair Value Measurement - Summary of Maturity Profile of Financial Liabilities Based on Contractual Undiscounted Payments (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	£ 49,670	£ 31,200
Bank loan [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	22,669	23,849
lease [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	20,295	536
Convertible Loan [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments		2,245
Trade And Other Payables [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	6,352	4,570
Contingent consideration liability[Member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	354
Within one year [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	26,525	13,245
Within one year [member] | Bank loan [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	17,185	8,260
Within one year [member] | lease [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	2,634	332
Within one year [member] | Convertible Loan [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments		83
Within one year [member] | Trade And Other Payables [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	6,352	4,570
Within one year [member] | Contingent consideration liability[Member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	354
After one year but not more than three years [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	10,127	17,955
After one year but not more than three years [member] | Bank loan [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	5,484	15,589
After one year but not more than three years [member] | lease [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	4,643	204
After one year but not more than three years [member] | Convertible Loan [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments		£ 2,162
LaterThanThreeYearsAndNotLaterThanFiveYearsMember [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	4,913
LaterThanThreeYearsAndNotLaterThanFiveYearsMember [Member] | lease [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	4,913
Later than five years [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	8,105
Later than five years [member] | lease [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	£ 8,105

Financial and Capital Risk Ma_8

Financial and Capital Risk Management and Fair Value Measurement - Detailed Information About Cash And Cash Equivalents By Currency Type (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Detailed Information about Cash and Cash Equivalents by Currency Type [Line Items]
Cash and cash equivalents	£ 16,347	£ 25,042	£ 50,045	£ 53,578
Pound Sterling [Member]
Detailed Information about Cash and Cash Equivalents by Currency Type [Line Items]
Cash and cash equivalents	2,525	23,189
US Dollar [Member]
Detailed Information about Cash and Cash Equivalents by Currency Type [Line Items]
Cash and cash equivalents	13,807	1,809
Swiss Francs [Member]
Detailed Information about Cash and Cash Equivalents by Currency Type [Line Items]
Cash and cash equivalents	11
Euro [Member]
Detailed Information about Cash and Cash Equivalents by Currency Type [Line Items]
Cash and cash equivalents	£ 4	£ 44

Financial and Capital Risk Ma_9

Financial and Capital Risk Management and Fair Value Measurement - Detailed Information About Gain Loss On Foreign Currency Translaction Recognized In Income Statement (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about financial instruments [line items]
Net foreign exchange gain/(loss)	£ 483	£ (44)	£ (1,384)
Market Uncertainty [member]
Disclosure of detailed information about financial instruments [line items]
Net foreign exchange gain/(loss)	(1,037)	(1,972)
US Dollar [Member] | Market Uncertainty [member]
Disclosure of detailed information about financial instruments [line items]
Net foreign exchange gain/(loss)	(219)	(542)
Swiss Francs [Member] | Market Uncertainty [member]
Disclosure of detailed information about financial instruments [line items]
Net foreign exchange gain/(loss)	(6)
Euro [Member] | Market Uncertainty [member]
Disclosure of detailed information about financial instruments [line items]
Net foreign exchange gain/(loss)	£ (812)	£ (1,430)

Financial and Capital Risk M_10

Financial and Capital Risk Management and Fair Value Measurement - Details the Group's Sensitivity to a 10% Change in the Period-End Rate (Detail) € in Thousands, £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019GBP (£)	Dec. 31, 2019USD ($)	Dec. 31, 2019EUR (€)	Dec. 31, 2018GBP (£)	Dec. 31, 2018USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2017GBP (£)	Dec. 31, 2019EUR (€)	Dec. 31, 2018EUR (€)
Statement [line items]
Loss before tax	£ (41,118)			£ (37,306)			£ (46,951)
Currency risk [member]
Statement [line items]
Loss before tax		$ 20	€ 74		$ 49	€ 130
Equity		$ 20			$ 49			€ 74	€ 130

Share-based Payments - Charge f

Share-based Payments - Charge for Share-based Payments Under IFRS 2 (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	£ 1,636	£ 2,190	£ 3,652
2019 Equity Incentive Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	635
2019 Non-Executive Director Equity Incentive Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	160
2015 Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	63	806	2,442
Mereo BioPharma Group plc Share Option Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	685	1,064	586
Long-term incentive plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	£ 93	£ 320	299
Deferred bonus share plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments			£ 325

Share-based Payments - Addition

Share-based Payments - Additional Information (Detail)	Feb. 20, 2020shares	Dec. 31, 2019GBP (£)£ / sharesshares	Dec. 31, 2019GBP (£)£ / sharesshares	Dec. 31, 2019GBP (£)£ / sharesshares	Dec. 31, 2019GBP (£)shares£ / shares	Dec. 31, 2018GBP (£)	Dec. 31, 2017	Dec. 31, 2019$ / shares
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of shares each ADR represent | shares					5
Number of options granted | shares	962,836
Number of shares granted, but not yet paid | shares					429,448
Fair value of ordinary shares		£ 3.10	£ 3.10	£ 3.10	£ 3.10
Amount of shares granted | shares					1.3
Changes in cumulative compensation expense			£ 100,000
2015 Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Weighted average remaining contractual life for the share options outstanding period		5 years 7 months 6 days				6 years 7 months 6 days
Number of share options expired in share-based payment arrangement | shares					0
2015 Plan [member] | Existing Non-Executive Directors [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Vesting period		4 years
2015 Plan [member] | Newly Non-Executive Directors [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Vesting period		3 years
2015 Plan [member] | Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price | £ / shares		£ 1.29	£ 1.29	£ 1.29	£ 1.29
2015 Plan [member] | Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price | £ / shares		£ 2.21	£ 2.21	£ 2.21	£ 2.21
Mereo BioPharma Group plc Share Option Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options granted						388,000	1,593,188
Weighted average remaining contractual life for the share options outstanding period		7 years 7 months 6 days				8 years 7 months 6 days
Weighted average fair value of options granted		£ 0	£ 0	£ 0	£ 0	£ 2.29
Mereo BioPharma Group plc Share Option Plan [member] | Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price | £ / shares		£ 2.76	£ 2.76	£ 2.76	£ 2.76
Mereo BioPharma Group plc Share Option Plan [member] | Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price | £ / shares		£ 3.25	£ 3.25	£ 3.25	£ 3.25
Long-term incentive plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options granted							185,950
Weighted average remaining contractual life for the share options outstanding period		10 months 24 days				1 year 9 months 18 days
Weighted average fair value of options granted		£ 0	£ 0	£ 0	£ 0	£ 0
Percentage of options issued to employees		75.00%	75.00%	75.00%	75.00%
Percentage of options vested to employees		25.00%	25.00%	25.00%	25.00%
Employee services expense			£ 100,000			£ 300,000
Number of share options expired in share-based payment arrangement				241,374
Deferred bonus share plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options granted				0	0	0	0
Weighted average remaining contractual life for the share options outstanding period		1 year 7 months 6 days				2 years 7 months 6 days
Weighted average fair value of options granted		£ 0	0	£ 0	£ 0	£ 0
Annual bonus payable in deferred shares				30.00%
2019 Equity Incentive Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Contractual term share options		10 years
Number of options granted				801,200
Weighted average remaining contractual life for the share options outstanding period		9 years 6 months
Weighted average fair value of options granted		£ 0.49	0.49	£ 0.49	0.49	0
Number of share options expired in share-based payment arrangement				3,150
2019 Equity Incentive Plan [member] | Newly Non-Executive Directors [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Vesting period		3 years
2019 Equity Incentive Plan [member] | Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price | $ / shares								$ 2.60
2019 Equity Incentive Plan [member] | Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price | $ / shares								$ 5.40
2019 Non-Executive Director Equity Incentive Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Contractual term share options		10 years
Number of options granted				77,000
Weighted average remaining contractual life for the share options outstanding period		9 years 6 months
Weighted average fair value of options granted		£ 0.49	£ 0.49	£ 0.49	£ 0.49	£ 0
2019 Non-Executive Director Equity Incentive Plan [member] | Existing Non-Executive Directors [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Vesting period		1 year
2019 Non-Executive Director Equity Incentive Plan [member] | Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price | £ / shares		£ 3	£ 3	£ 3	£ 3
2019 Non-Executive Director Equity Incentive Plan [member] | Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price | £ / shares		£ 5.40	£ 5.40	£ 5.40	£ 5.40
AstraZeneca [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share issued upon consideration | shares		1,349,693	1,349,693	1,349,693	1,349,693
Deferred Bonus Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Annual bonus payable in deferred shares						100.00%
Percentage of annual bonus granted to directors						30.00%

Share-based Payments - Summary

Share-based Payments - Summary of Number and Weighted Average Exercise Prices (WAEP) of, and Movements in, Options (Detail)	Feb. 20, 2020shares	Dec. 31, 2019sharesNumber£ / shares	Dec. 31, 2019sharesNumber£ / shares$ / shares	Dec. 31, 2018£ / shares	Dec. 31, 2017£ / shares	Dec. 31, 2019Number$ / shares
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options over ADR's Number granted during the year | shares	962,836
2019 Equity Incentive Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options over ADR's Number granted during the year		801,200	801,200
Options over ADR's Number cancelled during the year		3,150	3,150
Options over ADR's Number outstanding at December 31		798,050	798,050
WAEP options granted during the year | $ / shares			$ 4.29
WAEP options cancelled during the year | $ / shares			5.40
WAEP options outstanding at December 31 | $ / shares			$ 4.29
2019 Non-Executive Director Equity Incentive Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options over ADR's Number granted during the year		77,000	77,000
Options over ADR's Number outstanding at December 31		77,000	77,000
Options over ADR's Number exercisable at December 31		38,472	38,472			38,472
WAEP options granted during the year | $ / shares			$ 4.20
WAEP options outstanding at December 31 | $ / shares			$ 4.20
WAEP options exercisable at December 31 | $ / shares						$ 4.40
2015 Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options over ADR's Number outstanding at beginning of the year		8,983,133	8,983,133	9,124,610	9,198,655
Options over ADR's Number cancelled during the year | shares		0	0
Options over ADR's Number forfeited during the year		(59,533)	(59,533)	(46,255)	(74,045)
Options over ADR's Number exercised during the year				(95,222)
Options over ADR's Number outstanding at December 31		8,923,600	8,923,600	8,983,133	9,124,610
Options over ADR's Number exercisable at December 31		8,901,478	8,901,478	8,007,029	5,655,676	8,901,478
WAEP options outstanding at beginning of the year		£ 1.32		£ 1.32	£ 1.32
WAEP options forfeited during the year		1.29		1.29	1.29
WAEP options exercised during the year				1.29
WAEP options outstanding at December 31		1.32		1.32	1.32
WAEP options exercisable at December 31		£ 1.32	$ 1.32	£ 1.31	£ 1.31
Mereo BioPharma Group plc Share Option Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options over ADR's Number outstanding at beginning of the year		1,881,555	1,881,555	1,578,188
Options over ADR's Number granted during the year				388,000	1,593,188
Options over ADR's Number forfeited during the year		(357,490)	(357,490)	(84,633)	(15,000)
Options over ADR's Number outstanding at December 31		1,524,065	1,524,065	1,881,555	1,578,188
Options over ADR's Number exercisable at December 31 | Number		40,141	40,141			40,141
WAEP options outstanding at beginning of the year		£ 3.10		£ 3.05
WAEP options granted during the year				3.14	£ 3.05
WAEP options forfeited during the year		3.21		3.03	3.03
WAEP options outstanding at December 31		3.07		£ 3.10	£ 3.05
WAEP options exercisable at December 31		£ 3.03	$ 3.03

Share-based Payments - Summar_2

Share-based Payments - Summary of Weighted Average Inputs to the Models Used for the Fair Value of Share Options Granted (Detail) - £ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Long-term incentive plan [member] | Monte carlo option pricing model [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)			51.70%
Market price of ordinary shares (£)			£ 3.03
Model used			    Monte Carlo
Long-term incentive plan [member] | Black scholes option pricing model [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)			51.70%
Risk-free interest rate (%)			0.39%
Expected life of share options (years)			5 years
Market price of ordinary shares (£)			£ 3.03
Model used			Black Scholes
2019 Equity Incentive Plan [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)	66.00%
Risk-free interest rate (%)	0.95%
Expected life of share options (years)	10 years
Market price of ordinary shares (£)	£ 0.66
Model used	Black Scholes
2019 Non-Executive Director Equity Incentive Plan [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)	66.00%
Risk-free interest rate (%)	0.97%
Expected life of share options (years)	10 years
Market price of ordinary shares (£)	£ 0.63
Model used	Black Scholes
Share option plan grants [member]
Disclosure of classes of share capital [line items]
Expected life of share options (years)		10 years
Model used		Black Scholes
Bottom of range [member] | Long-term incentive plan [member] | Monte carlo option pricing model [member]
Disclosure of classes of share capital [line items]
Risk-free interest rate (%)			0.17%
Expected life of share options (years)			3 years
Bottom of range [member] | Share option plan grants [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)		65.00%
Risk-free interest rate (%)		1.39%
Market price of ordinary shares (£)		£ 2.76
Top of range [member] | Long-term incentive plan [member] | Monte carlo option pricing model [member]
Disclosure of classes of share capital [line items]
Risk-free interest rate (%)			0.39%
Expected life of share options (years)			5 years
Top of range [member] | Share option plan grants [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)		67.00%
Risk-free interest rate (%)		1.53%
Market price of ordinary shares (£)		£ 3.25

Share-based Payments - Summar_3

Share-based Payments - Summary of Number and Movements in Long Term Incentive Plan Options (Detail)	Feb. 20, 2020shares	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Granted during the year	962,836
Long-term incentive plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Granted during the year				185,950
Lapsed during the year		(241,374)
Options over ADR's Number outstanding at December 31		910,072	1,151,446	1,151,446
Exercisable at December 31		0	0	0

Share-based Payments - Summar_4

Share-based Payments - Summary of Number and Movements in Deferred Bonus Share Plan (Detail)	Feb. 20, 2020shares	Dec. 31, 2019	Dec. 31, 2019shares	Dec. 31, 2018	Dec. 31, 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Granted during the year	962,836
Deferred bonus share plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options over ADR's Number outstanding at beginning of the year		163,000		163,000	62,180
Awarded during the year					100,820
Granted during the year		0	0	0	0
Options over ADR's Number outstanding at December 31		163,000		163,000	163,000
Exercisable at December 31		0	0	0	0

Commitments and Contingencies -

Commitments and Contingencies - Summary of Future Minimum Lease Payments under Non-cancellable Operating Leases (Detail) £ in Thousands	Dec. 31, 2019GBP (£)
Disclosure of maturity analysis of operating lease payments [line items]
Non cancellable operating leases	£ 552
Within one year [member]
Disclosure of maturity analysis of operating lease payments [line items]
Non cancellable operating leases	£ 552

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Detail) £ in Thousands, $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2017USD ($)shares	Dec. 31, 2019GBP (£)	Dec. 31, 2018GBP (£)
Disclosure of commitments and contingencies [line items]
Lease remaining period		12 months
Finance leases | £		£ 0	£ 0
Mereo BioPharma 4 Limited [member]
Disclosure of commitments and contingencies [line items]
Payment of ordinary shares	$ 3
Issuance of aggregate ordinary shares | shares	490,798
Aggregate upfront payment amount	$ 5
Payments of aggregate and issue additional ordinary shares	$ 115.5
Bottom of range [member]
Disclosure of commitments and contingencies [line items]
Lease term		1 year
Top of range [member]
Disclosure of commitments and contingencies [line items]
Lease term		2 years

Related Party Disclosures - Add

Related Party Disclosures - Additional Information (Detail) £ / shares in Units, £ in Thousands, $ in Millions	Jun. 21, 2019GBP (£)£ / sharesshares	Apr. 26, 2017GBP (£)	Dec. 31, 2019GBP (£)shares	Dec. 31, 2018GBP (£)shares	Feb. 10, 2020GBP (£)	Feb. 10, 2020USD ($)
Disclosure of transactions between related parties [line items]
Amount paid to trust by the company			£ 1,000	£ 300
Shares purchased by the EBT | shares			1,074,274	163,000
Cash balance held by the EBT			£ 21,762	£ 21,762
Conversion of loan notes into ordinary shares amount	£ 2,400	£ 1,398,552
Novartis [member]
Disclosure of transactions between related parties [line items]
Conversion of loan notes into ordinary shares amount	£ 2,400
Number of converted loans converted to ordinary shares | shares	1,071,042
Conversion price per share | £ / shares	£ 2.21
Bonus shares | shares	864,966
Novartis Pharma AG [member]
Disclosure of transactions between related parties [line items]
Debt instrument face value					£ 3,800	$ 5

Related Party Disclosures - Sum

Related Party Disclosures - Summary Of Compensation of key management personnel of the Group (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of transactions between related parties [abstract]
Short-term benefits	£ 3,488	£ 3,176	£ 2,757
Post-employment benefits	64	60	87
IFRS 2 share-based payment charge	1,152	1,470	2,726
Total compensation paid to key management personnel	£ 4,704	£ 4,706	£ 5,570

Events after the reporting pe_2

Events after the reporting period - Additional Information (Detail) £ / shares in Units, $ / shares in Units, £ in Millions

Aug. 07, 2020GBP (£)

Jun. 30, 2020shares

Jun. 03, 2020GBP (£)Directors£ / sharesshares

Jun. 03, 2020USD ($)

Feb. 20, 2020shares£ / shares

Feb. 20, 2020shares$ / shares

Feb. 19, 2020USD ($)$ / sharesshares

Feb. 10, 2020USD ($)

Jan. 31, 2020USD ($)

Dec. 31, 2019GBP (£)$ / shares

Feb. 19, 2020£ / shares

Feb. 10, 2020GBP (£)£ / sharesshares

Feb. 10, 2020USD ($)$ / sharesshares

Feb. 08, 2020$ / shares

Dec. 31, 2019USD ($)

Jun. 21, 2019£ / shares

Jun. 21, 2019$ / shares

Dec. 31, 2018GBP (£)

Apr. 26, 2017£ / shares

Statement [line items]

Share based compensation by share based payment arrangement options granted

962,836

962,836

Par value per share | £ / shares

£ 0.003

£ 0.003

Warrants [Member]

Statement [line items]

Warrants issued

362,534

362,534

Exercise price | £ / shares

£ 2.95

Novartis [member]

Statement [line items]

Debt instrument face value | £

£ 2.9

Conversion price per share | $ / shares

$ 2.21

Events After Reporting Date [member] | Aspire Capital Securities Purchase Agreement [Member] | Aspire Capital LLC [Member] | Ordinary shares [member]

Statement [line items]

Common stock shares issuable

2,862,595

2,862,595

Events After Reporting Date [member] | Aspire Capital Securities Purchase Agreement [Member] | Aspire Capital LLC [Member] | American depository shares [Member]

Statement [line items]

Commitement to issue capital | $

$ 28,000,000

Common stock shares issuable

572,519

572,519

Events After Reporting Date [member] | Aspire Capital Securities Initial Purchase Agreement [Member] | Aspire Capital LLC [Member]

Statement [line items]

Commitement to issue capital | $

$ 3,000,000

Proceeds from ordinary shares | $

$ 3,000,000

Discount percentage on market price of shares issued

16.00%

16.00%

Closing market price of share | $ / shares

$ 1.56

Issue price per share | $ / shares

$ 1.31

Period over which the commitement is to be fulfilled

30 months

Events After Reporting Date [member] | Aspire Capital Securities Initial Purchase Agreement [Member] | Aspire Capital LLC [Member] | Additional Commitement To Issue Capital [Member]

Statement [line items]

Commitement to issue capital | $

$ 25,000,000

Events After Reporting Date [member] | Aspire Capital Securities Initial Purchase Agreement [Member] | Aspire Capital LLC [Member] | Ordinary shares [member]

Statement [line items]

Common stock shares issued

11,423,925

11,423,925

Events After Reporting Date [member] | Aspire Capital Securities Initial Purchase Agreement [Member] | Aspire Capital LLC [Member] | American depository shares [Member]

Statement [line items]

Common stock shares issued

2,286,585

2,286,585

Global Licensing Agreement [member] | Events After Reporting Date [member]

Statement [line items]

Upfront Payment Received | $

$ 4,000,000

Additional milestone payment | $

2,000,000

Milestone payment for regulatory and commercial achievements | $

$ 300,000,000

Mereo CVR Agreement [member]

Statement [line items]

Contingent Consideration Payable

£ 0.4

$ 500,000

Mereo Two Thousand And Nineteen NED Equity incentive Plan [member]

Statement [line items]

Share based compensation by share based payment arrangement options granted

77,000

Share based compensation by share based payment arrangement exercise price per option | $ / shares

£ 4.20

Major business combination [member] | NAVI milestones [member] | Events After Reporting Date [member]

Statement [line items]

Eligible percentage of cash equal to milestone payment

70.00%

Major business combination [member] | NAVI milestones [member] | Top of range [member] | Events After Reporting Date [member]

Statement [line items]

Maximum cash payment limit | $

$ 79,700,000

Equity Financing Agreement [Member] | Events After Reporting Date [member] | Convertible Loan Notes [Member]

Statement [line items]

Debt instrument face value | £

£ 3.8

Equity Financing Agreement [Member] | Events After Reporting Date [member] | Convertible Loan Notes [Member] | Novartis [member]

Statement [line items]

Debt instrument face value | £

£ 3.8

Conversion price per share | £ / shares

£ 0.265

Debt instrument rate of interest

6.00%

6.00%

Debt maturity

three years

Number of securities called by warrants or rights

1,449,614

1,449,614

Exercise price of warrants | £ / shares

£ 0.265

Expiry date of warrants

Feb. 10, 2025

Securities Purchase Agreement [Member] | Events After Reporting Date [member] | Boxer Capital LLC [Member]

Statement [line items]

Commitement to issue capital | $

$ 3,000,000

Discount percentage on market price of shares issued

20.00%

Closing market price of share | $ / shares

$ 23.5

Issue price per share | £ / shares

£ 18.8

Securities Purchase Agreement [Member] | Events After Reporting Date [member] | Boxer Capital LLC [Member] | Ordinary shares [member]

Statement [line items]

Common stock shares issuable

12,252,715

Securities Purchase Agreement [Member] | Events After Reporting Date [member] | Boxer Capital LLC [Member] | American depository shares [Member]

Statement [line items]

Common stock shares issuable

2,450,543

Share Based Payments One [Member] | Mereo Two Thousand And Nineteen NED Equity incentive Plan [member] | Events After Reporting Date [member] | Existing Non Executive Directors [Member]

Statement [line items]

Share based compensation by share based payment arrangement options granted

77,000

77,000

Share Based Payments One [Member] | Mereo Two Thousand And Nineteen NED Equity incentive Plan [member] | Events After Reporting Date [member] | American depository shares [Member] | Existing Non Executive Directors [Member]

Statement [line items]

Share based compensation by share based payment arrangement exercise price per option | $ / shares

$ 1.84

$ 1.84

Private placement [Member]

Statement [line items]

Common stock shares issued

89,100,000

Private Placement Offerings

£ 56

$ 70,000,000

Repayments Of Current Debt

10.4

13,000,000

Interest on Current Debt

14.1

17,600,000

Proceeds from Issuance of Private Placement

£ 15.5

19,400,000

Par value per share | £ / shares

£ 0.003

Tranche 1 Notes [Member]

Statement [line items]

Common stock shares issued

40,533,671

Proceeds from Issuance of Private Placement | £

£ 40.5

Proceeds from Issuance of Convertible Notes

£ 40.5

$ 50,600,000

Conversion Of Notes Shares Converted

21,674,143

Conversion Of Notes Ordinary Shares Converted

124,564,033

Conversion Of Notes Balance Shares

18,859,528

Note Instrument Maturity Date

June 2023

June 2023

Note Instrument Extended Maturity Term

10 years

10 years

Fixed Interest Rate of Note Instrument

10.00%

Reduced Fixed Interest Rate of Note Instrument

6.00%

Percentage of price per share

17.40%

Percentage of voting right

9.99%

Tranche 2 Notes [Member]

Statement [line items]

Common stock shares issued

115,034,554

Proceeds from Issuance of Convertible Notes | £

£ 40

Note Instrument Maturity Date

2026

2026

Note Instrument Extended Maturity Term

10 years

10 years

Fixed Interest Rate of Note Instrument

2.00%

Tranche 3 Notes [Member]

Statement [line items]

Proceeds from Issuance of Convertible Notes | £

£ 56

Note Instrument Maturity Date

August 2025

August 2025

Note Instrument Extended Maturity Term

10 years

10 years

Fixed Interest Rate of Note Instrument

2.00%

Percentage of voting right

9.99%

Subsequent Event [Member]

Statement [line items]

Exercise price of warrants | £ / shares

£ 34.8

Warrants issued

161,048,366

Commission Expenses | $

$ 325,000

Percentage of price per share

200.00%

Percentage Number of shares issuable

50.00%

Subsequent Event [Member] | OrbiMed [Member]

Statement [line items]

Maximum number of directors | Directors

9

Equity Fund Raise [Member]

Statement [line items]

Perecntage of voting shares representing in favour of resolution

40.00%

Material Liabilities | £

£ 137.1