Mereo BioPharma (MREO) 20-F/A 29 May 19 2018 FY Annual report (foreign) (amended) Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2018shares
Document and entity information [abstract]
Document Type	20-F/A
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
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	71,240,272

Consolidated statement of compr

Consolidated statement of comprehensive loss - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of comprehensive income [abstract]
Research and development expenses	£ (22,703,553)	£ (34,606,649)	£ (24,562,502)
Administrative expenses	(12,504,887)	(10,697,194)	(11,616,816)
Operating loss	(35,208,440)	(45,303,843)	(36,179,318)
Finance income	306,831	826,855	374,906
Finance charge	(2,360,648)	(1,089,925)	(179,765)
Net foreign exchange gain/(loss)	(43,863)	(1,384,225)	2,262,626
Loss before tax	(37,306,120)	(46,951,138)	(33,721,551)
Taxation	5,277,380	8,152,084	5,331,271
Loss attributable to equity holders of the parent	(32,028,740)	(38,799,054)	(28,390,280)
Other comprehensive income for the year, net of tax	0	0	0
Total comprehensive loss for the year, net of tax and attributable to the equity holders of the parent	£ (32,028,740)	£ (38,799,054)	£ (28,390,280)
Basic and diluted loss per share	£ (0.45)	£ (0.56)	£ (0.63)

Consolidated balance sheet

Consolidated balance sheet - GBP (£)	Dec. 31, 2018	Dec. 31, 2017
Non-current assets
Property, plant and equipment	£ 148,934	£ 153,361
Intangible assets	32,632,229	33,005,229
Total non-current assets	32,781,164	33,158,590
Current assets
Prepayments	1,066,932	1,970,781
R&D tax credits	5,277,380	8,152,084
Other receivables	608,893	509,350
Short-term investments	2,500,000	2,500,000
Cash and short-term deposits	25,041,945	50,044,672
Total current assets	34,495,150	63,176,887
Total assets	67,276,314	96,335,477
Equity
Issued capital	213,721	213,285
Share premium	118,492,073	118,226,956
Other capital reserves	18,592,618	16,359,169
Employee Benefit Trust shares	(306,838)
Other reserves	7,000,000	7,000,000
Accumulated loss	(111,220,794)	(79,315,920)
Total equity	32,770,780	62,483,490
Non-current liabilities
Provisions	2,641,353	4,075,386
Interest-bearing loans and borrowings	14,646,753	18,812,511
Warrant liability	1,005,613	1,346,484
Other liabilities	34,289
Total non-current liabilities	18,328,008	24,234,381
Current liabilities
Trade and other payables	4,570,307	3,024,026
Accruals	4,437,321	4,379,774
Provisions	332,014	274,000
Interest-bearing loans and borrowings	6,837,884	1,939,806
Total current liabilities	16,177,526	9,617,606
Total liabilities	34,505,534	33,851,987
Total equity and liabilities	£ 67,276,314	£ 96,335,477

Consolidated statement of cash

Consolidated statement of cash flows - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Loss before tax	£ (37,306,120)	£ (46,951,138)	£ (33,721,551)
Adjustments to reconcile loss before tax to net cash flows:
Depreciation of property, plant and equipment	37,796	36,076	32,940
Share-based payment expense	2,189,293	3,651,898	6,494,018
Net foreign exchange loss	43,863	1,384,225	(2,262,626)
Provision for social security contributions on employee share options	(1,446,019)	1,115,966	1,031,109
Provision for deferred cash consideration	443,000		(374,906)
Interest earned	(306,831)	(826,855)
Finance charges	1,917,649	1,089,925	179,765
Modification loss on bank loan	730,037
Working capital adjustments:
(Decrease)/Increase in receivables	804,306	(839,751)	(1,219,202)
Increase in payables	1,603,828	3,860,412	(768,402)
Tax received	8,152,085	5,331,271	946,681
Net cash flows from operating activities	(23,137,113)	(32,147,971)	(29,662,174)
Investing activities
Purchase of property, plant and equipment	(35,536)	(15,568)	(3,467)
Purchase of license		(2,280,000)
Disposal of property, plant and equipment	2,166		1,175
Short-term investments		(2,500,000)
Interest earned	284,928	1,051,620	374,906
Net cash flows from (used in) investing activities	251,558	(3,743,948)	372,614
Financing activities
Proceeds from issue of ordinary shares	273,064	15,000,000	67,888,820
Transaction costs on issue of shares	(7,511)	(729,632)	(2,995,864)
Proceeds from issue of convertible loan			3,463,563
Proceeds from issue of bank loan	455,000	20,000,000
Transaction costs on bank loan	(920,859)	(200,000)
Interest paid on bank loan	(1,644,610)	(327,123)
Proceeds from TAP agreement	78,445
Purchase of treasury shares	(306,838)
Net cash flows from (used in) financing activities	(2,073,309)	33,743,245	68,356,519
Net (decrease) in cash and cash equivalents	(24,958,864)	(2,148,674)	39,066,959
Cash and cash equivalents, beginning balance	50,044,672	53,577,571	12,247,986
Effect of exchange rate changes on cash and cash equivalents	(43,863)	(1,384,225)	2,262,626
Cash and cash equivalents, ending balance	£ 25,041,945	£ 50,044,672	£ 53,577,571

Consolidated statement of chang

Consolidated statement of changes in equity - GBP (£)	Total	Share options [member]	LTIPs [member]	Deferred bonus shares [member]	Deferred equity consideration [member]	Conversion of loan note [member]	April 4, 2017 [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 4, 2017 [member]	Issued capital [member]October 31, 2017 [member]	Issued capital [member]June 1, 2018 [member]	Issued capital [member]August 3, 2018 [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]April 4, 2017 [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]Novartis bonus shares [member]	Employee Benefit Trust [member]	Other reserves [member]	Accumulated Losses [member]
Beginning balance at Dec. 31, 2015	£ 62,483,490											£ 213,285								£ 118,226,956								£ 16,359,169							£ 7,000,000	£ (79,315,920)
Loss for the year	(28,390,280)																																			(28,390,280)
Issue of share capital	67,888,821											107,709								67,781,112
Issue of share capital												26,092								15,977,271								(16,003,363)
Share-based payments	6,494,018	£ 6,185,067	£ 133,601	£ 175,350																									£ 6,185,067	£ 133,601	£ 175,350
Equity element of convertible loan	516,802																											516,802
Share capital reduction																				(7,000,000)															7,000,000
Transaction costs on issuance of share capital	(2,995,864)																			(2,995,864)
Ending balance at Dec. 31, 2016	79,256,742											193,022								99,975,399								12,667,562							7,000,000	(40,579,241)
Loss for the year	(38,799,054)																																			(38,799,054)
Issue of share capital						£ 1,398,553	£ 15,000,000	£ 1,520,000					£ 1,899	£ 1,766	£ 15,125	£ 1,473					£ 1,396,654	£ 1,081,133	£ 14,984,875	£ 1,518,527									£ (1,082,899)
Share-based payments		3,027,963	298,287	£ 325,648	£ 1,331,288																								3,027,963	298,287	£ 325,648	£ 1,331,288
Equity element of convertible loan	(208,680)																											(208,680)
Conversion of convertible loan	62,375																																			62,375
Transaction costs on issuance of share capital	(729,632)																			(729,632)
Ending balance at Dec. 31, 2017	62,483,490											213,285								118,226,956								16,359,169							7,000,000	(79,315,920)
Loss for the year	(32,028,740)																																			(32,028,740)
Issue of share capital									£ 150,228	£ 12,900	£ 109,936						£ 150	£ 30	£ 256						£ 150,078	£ 12,870	£ 109,680
Adoption of IFRS 9	123,866																																			123,866
Share-based payments		£ 1,869,955	£ 319,338																										£ 1,869,955	£ 319,338
Issue of warrants for TAP agreement	44,156																											44,156
Transaction costs on issuance of share capital	(7,511)																			(7,511)
Purchase of treasury shares	(306,838)																																	£ (306,838)
Ending balance at Dec. 31, 2018	£ 32,770,780											£ 213,721								£ 118,492,073								£ 18,592,618						£ (306,838)	£ 7,000,000	£ (11,120,794)

Corporate information

Corporate information	12 Months Ended
	Dec. 31, 2018
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 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”. As of April 24, 2019, we are also listed on the Nasdaq Global Exchange via American Depositary Receipts (ADRs) under the ticker symbol “MREO” following the completion of the merger with OncoMed Pharmaceuticals, Inc. (“OncoMed”). Our registered office is located at Fourth Floor, 1 Cavendish Place, London W1G 0QF. The consolidated financial statements of Mereo BioPharma Group plc and its subsidiaries (collectively, the “Group”) for the year ended December 31, 2018 were authorized for issue in accordance with a resolution of the directors on April 26, 2019.

Significant accounting policies

Significant accounting policies	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Significant accounting policies	2. Significant accounting policies 2.1 Basis of preparation The Group’s annual financial statements have been prepared in accordance with International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). The financial information is presented in pounds sterling (“Sterling”). 2.2 Adoption of new accounting policies The following policies have been adopted since the start of the period: a) IFRS 9 Financial Instruments. In the current period the Group has applied IFRS 9 Financial Instruments (as revised in July 2014) and the related consequential amendments to other IFRS. IFRS 9 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 Interest-bearing loans and borrowings – convertible loan notes (in £) At January 1, 2018 calculated under IAS 39 1,977,393 Amounts restated through retained earnings (123,865 ) At January 1, 2018 under IFRS 9 1,853,528 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. b) IFRS 15 Revenue from Contracts with Customers In the current period the Group has adopted IFRS 15 Revenue from Contracts with Customers. The new revenue standard is applicable to all entities and will supersede all current revenue recognition requirements under IFRS. There has been no impact on Group reporting in the period. c) IFRS 16 Leases General impact of application of IFRS 16 Leases IFRS 16 provides a comprehensive model for the identification of lease arrangements and their treatment in the financial statements for both lessors and lessees. IFRS 16 will supersede the current lease guidance including IAS 17 Leases and the related Interpretations when it becomes effective for accounting periods beginning on or after January 1, 2019. The date of initial application of IFRS 16 for the Group will be January 1, 2019. The Group has chosen the modified retrospective application of IFRS 16 in accordance with IFRS 16:C5(b). Consequently, the Group will not restate the comparative information. In contrast to lessee accounting, IFRS 16 substantially carries forward the lessor accounting requirements in IAS 17. Impact of the new definition of a lease The Group will make use of the practical expedient available on transition to IFRS 16 not to reassess whether a contract is or contains a lease. Accordingly, the definition of a lease in accordance with IAS 17 and IFRIC 4 will continue to apply to those leases entered or modified before 1 January 2019. The change in definition of a lease mainly relates to the concept of control. IFRS 16 distinguishes between leases and service contracts on the basis of whether the use of an identified asset is controlled by the customer. Control is considered to exist if the customer has: • the right to obtain substantially all of the economic benefits from the use of an identified asset; and • the right to direct the use of that asset. The Group will apply the definition of a lease and related guidance set out in IFRS 16 to all lease contracts entered into or modified on or after January 1, 2019 (whether it is a lessor or a lessee in the lease contract). In preparation for the first-time application of IFRS 16, the Group has carried out an implementation project. The project has shown that the new definition in IFRS 16 will not change significantly the scope of contracts that meet the definition of a lease for the Group. Impact on lessee accounting IFRS 16 will change how the Group accounts for leases previously classified as operating leases under IAS 17, which were off-balance On initial application of IFRS 16, for all leases (except as noted below), the Group will: a) recognize right-of-use b) recognize depreciation of right-of-use c) separate the total amount of cash paid into a principal portion (presented within financing activities) and interest (presented within operating activities) in the consolidated cash flow statement. Lease incentives (e.g. rent-free period) will be recognized as part of the measurement of the right-of-use Under IFRS 16, right-of-use For short-term leases (lease term of 12 months or less) and leases of low-value As at December 31, 2018, the Group had non-cancellable The non-cancellable non-cancellable A preliminary assessment indicates that all of these arrangements relate to leases other than short-term leases and leases of low-value right-of-use right-to-use The preliminary assessment indicates that £nil of these arrangements relate to short-term leases and leases of low-value Under IAS 17, all lease payments on operating leases are presented as part of cash flows from operating activities. The impact of the changes under IFRS 16 to the 2019 statement of cash flows would be to reduce the cash used in operating activities by £932,268 and to increase net cash used in financing activities by the same amount. 2.3 Going concern Though 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 research 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 by way of the completed merger with OncoMed (as described more fully in Note 29) 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. 2.4 Basis of consolidation The consolidated financial information comprises the financial statements of Mereo BioPharma Group plc and its subsidiaries as at December 31, 2018. 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. All Group subsidiaries prepare yearly financial information to December 31 consistent with the Company. 2.5 Summary of significant accounting policies a) Taxes Current income tax Current income tax assets and liabilities are measured at the amount expected to be recovered from or paid to the taxation authorities, and include R&D tax credits receivable under the HM Revenue and Customs (HMRC) small or medium enterprise (SME) scheme, which provides additional taxation relief for qualifying expenditure on R&D activities, and allows for the surrender of tax losses in exchange for a cash payment from HMRC. Current income tax relating to items recognized directly in equity is recognized in equity and not in the statement of comprehensive loss. Income tax credit The Group benefits from the U.K. R&D tax credit regime whereby a portion of the Group’s losses can be surrendered for a cash rebate of up to 33.35% of eligible expenditures. Such credits are accounted for within the tax provision, in the year in which the expenditures were incurred. 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. b) Foreign currencies The functional currency of the Company and its subsidiaries is Sterling. 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 profit or loss. Gains or losses on the retranslation of foreign currency balances at the year end are recognized in the consolidated statement of comprehensive loss under net foreign exchange gains/(losses). 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 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) Leases Leases in which a significant portion of the risks and rewards of ownership are retained by the lessor are classified as operating leases. Payments made under operating leases (net of any incentives received from the lessor) are charged to the statement of comprehensive loss on a straight-line basis over the period of the lease. The Group leases its premises (see Note 26). The Company recognizes any lease incentives on a straight-line basis over the entire period of the lease, assuming that any break clauses available will not be exercised. By not exercising any break clauses, the Group receives a 50% rent discount from the landlord for a fixed period of time as described in Note 26. The determination of whether an arrangement is, or contains, a lease is based on the substance of the arrangement at the inception date. The arrangement is assessed for whether fulfilment of the arrangement is dependent on the use of a specific asset or assets or the arrangement conveys a right to use the asset or assets, even if that right is not explicitly specified in an arrangement. e) Intangible assets Intangible assets, relating to intellectual property rights acquired through licensing or assigning patents and know-how, f) 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. g) Impairment of non-financial Further disclosures relating to impairment of non-financial • Disclosures for significant assumptions Note 3 • Property, plant and equipment Note 11 • Intangible assets not yet available for use Notes 12 and 13 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 (CGU) 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 CGU 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 CGU’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. Intangible assets not yet available for use are tested for impairment annually as at December 31 at the CGU level, as appropriate, and when circumstances indicate that the carrying value may be impaired. An impairment test was performed at December 31, 2018. h) 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. i) Short-term investments Cash on deposit for terms greater than three months are recognized at fair value in the balance sheet. j) Provisions General 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 k) Share-based payments Employees (including senior 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 the Share Option Plan. Executive officers are also provided with 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 excludes the impact of any non-market Under the 2015 Plan, options were historically awarded to employees, NEDs and certain consultants. Share options awarded to non-employees non-employee 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. l) Costs of issuing capital The Group deducts directly attributable costs of issuing capital from the proceeds in accordance with IAS 39 Financial Instruments: Recognition and Measurement. 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. m) 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, representing the embedded option to convert the liability into equity of the Group, is included in equity. An exchange between an existing borrower and lender of debt instruments with substantially different terms are accounted for as an extinguishment of the original financial liability and the recognition of a new financial liability as per IAS 39 and IFRS 9. Similarly, a substantial modification of the terms of an existing financial liability, or a part of it (whether or not due to the financial difficulty of the debtor) should be accounted for as an extinguishment of the original financial liability and the recognition of a new financial liability. In line with IAS 39 the terms of exchanged or modified debt are regarded as substantially different if the net present value of the cash flows under the new terms (including any fees paid net of any fees received) discounted at the original effective interest rate is at least 10% different from the discounted present value of the remaining cash flows of the original debt instrument. Where such modifications are less than 10% different, the effective interest rate is adjusted to take account of the new terms. n) Employee Benefit Trust The Group operates an Employee Benefit Trust (EBT): Mereo BioPharma Group plc Employee Benefit Trust. The EBT has been established to fulfil awards made under the Deferred Bonus Share Plan and the Long Term Incentive 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. In compliance with IAS 32 Financial Instruments: Presentation Group, shares held by the EBT are included in the consolidated balance sheet as a reduction in equity. Gains and losses on Group shares are recognized directly in equity. The Group consolidated accounts treat the EBT as an extension of the Group and the Company as it is controlled and therefore consolidated. o) Research and development 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 p) 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. q) Bank loan and associated warrants After initial recognition, interest-bearing loans and borrowings are subsequently measured at amortized cost using the effective interest rate (EIR) method. The EIR amortization is included as a finance charge in the statement of comprehensive loss. This category applies to interest-bearing borrowings, trade and other payables. As the terms of the warrant instrument allow for a cashless exercise, in line with IAS 32 the associated warrants are measured at fair value with changes recorded through the statement of comprehensive loss (see Note 20). An exchange between an existing borrower and lender of debt instruments with substantially different terms are accounted for as an extinguishment of the original financial liability and the recognition of a new financial liability as per IAS 39 and IFRS 9. Similarly, a substantial modification of the terms of an existing financial liability, or a part of it, (whether or not due to the financial difficulty of the debtor) should be accounted for as an extinguishment of the original financial liability and the recognition of a new financial liability. In line with IAS 39 the terms of exchanged or modified debt are regarded as substantially different if the net present value of the cash flows under the new terms (including any fees paid net of any fees received) discounted at the original effective interest rate is at least 10% different from the discounted present value of the remaining cash flows of the original debt instrument. Where such modifications are less than 10% different, the effective interest rate is adjusted to take account of the new terms. r) The Alpha-1 The agreement is regarded as a compound instrument which includes both debt and equity components. As per IAS 32:31 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 re-measured,

Significant accounting judgment

Significant accounting judgments, estimates and assumptions	12 Months Ended
	Dec. 31, 2018
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Significant accounting judgments, estimates and assumptions	3. Significant accounting judgments, estimates and assumptions The preparation of the consolidated accounts 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. Judgements Share-based compensation Incentives in the form of shares are provided to employees under a share option plan, long-term incentive plan and deferred bonus share plan. The fair value of the employee services received in exchange for the grant of the options is recognized as an expense. The expense is based upon a number of assumptions disclosed in Note 25. The selection of different assumptions could affect the results of the Group. 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 13) and leasehold improvements, office equipment and IT equipment as at December 31, 2018. 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 judgments regarding the likelihood of successful product approval, the costs of reaching approval and the subsequent commercial profitability of the product once approved. Estimates 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. 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. Bank loan and associated warrants As part of the bank loan the Group has issued warrants to subscribe for shares. The fair value of the warrants issued is assessed at each balance sheet date based upon a number of estimates, as disclosed in Note 20.

Segment information

Segment information	12 Months Ended
	Dec. 31, 2018
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Segment information	4. Segment information Management views the business as a single portfolio of product candidates. Only R&D 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. All non-current The Company’s CODM is the executive management team (comprised of the Chief Executive Officer, Chief Financial Officer, Chief Medical Officer, General Counsel, the Head of Corporate Development and the Head of Patient Access and Commercial Planning) which manages the operating results of the business.

Group information

Group information	12 Months Ended
	Dec. 31, 2018
Investments accounted for using equity method [abstract]
Group information	5. Group information Information about subsidiaries The consolidated financial statements of the Group include: % equity interest December 31, Name Principal activities Country of incorporation 2017 2018 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 Mereo US Holdings Inc Holding U.S. — 100 Mereo MergerCo One Inc. Holding U.S. — 100 Mereo BioPharma Group plc Employee Benefit Trust Employee share scheme Jersey — —

Compensation of key management

Compensation of key management personnel of the Group	12 Months Ended
	Dec. 31, 2018
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Compensation of key management personnel of the Group	6. Compensation of key management personnel of the Group Key management includes directors (executive and non-executive) Year ended December 31, 2016 2017 2018 (in £) Short-term benefits 2,111,712 2,756,979 3,176,168 Post-employment benefits 106,500 87,269 59,522 IFRS 2 share-based payment charge 4,631,853 2,726,337 1,470,025 Total compensation paid to key management personnel 6,850,065 5,570,585 4,705,715

Finance income and Finance char

Finance income and Finance charge	12 Months Ended
	Dec. 31, 2018
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Finance income and Finance charge	7. Finance income and Finance charge Finance income Year ended December 31 2016 2017 2018 (in £) Bank interest earned 374,906 826,855 306,831 Finance charge Year ended December 31, 2016 2017 2018 (in £) Interest payable on convertible loan (179,765 ) (103,115 ) (185,352 ) Interest payable on bank loan — (327,123 ) (1,644,610 ) Accreted interest on bank loan — (66,935 ) (781,998 ) Transaction costs on bank loan — (200,000 ) — Loss on short-term deposits — (338,279 ) (21,903 ) Increase in provision for deferred cash consideration — — (443,000 ) Change in warrant fair value — (54,473 ) 716,214 Total finance charge (179,765 ) (1,089,925 ) (2,360,648 )

Employee benefits expense

Employee benefits expense	12 Months Ended
	Dec. 31, 2018
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Employee benefits expense	8. Employee benefits expense December 31, 2016 2017 2018 (in £) Included in research and development expenses: Salaries 1,150,222 1,640,373 1,791,679 Social security costs (See Note 19) 344,467 420,417 (29,670 ) Pension contributions 50,864 77,425 73,401 Share-based payment expense 1,550,884 822,173 525,972 Included in administrative expenses: Salaries 2,132,920 2,253,393 2,902,759 Social security costs 1,040,409 1,159,548 (827,509 ) Pension contributions 109,187 96,598 97,962 Share-based payment expense 4,943,133 2,829,725 1,663,322 Total employee benefits expense 11,322,086 9,299,652 6,197,916

Income tax

Income tax	12 Months Ended
	Dec. 31, 2018
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Income tax	9. Income tax The Group is entitled to claim tax credits in the U.K. under the U.K. R&D small or medium-sized Year ended December 31 2016 2017 2018 (in £) U.K. corporation tax R&D credit 5,331,271 8,152,084 5,277,380 Income tax credit 5,331,271 8,152,084 5,277,380 The charge for the year can be reconciled to the loss per the income statement as follows: Year-ended December 31, 2016 2017 2018 (in £) Loss on ordinary activities before income tax (33,721,551 ) (46,951,138 ) (37,306,120 ) Loss on ordinary activities before tax at the U.K.’s statutory income tax rate of 19% (2017: 19.25%) 6,744,310 9,038,094 7,088,163 Expenses not deductible for tax purposes (permanent differences) (15,116 ) (14,316 ) (1,069,606 ) Temporary timing differences (1,300,044 ) (711,677 ) (276,881 ) R&D relief uplift 2,134,107 3,447,474 2,270,777 Losses (unrecognized) (2,231,986 ) (3,784,801 ) (2,803,796 ) Deferred income from MBG loan guarantee costs — 177,310 68,723 Tax credit for the year 5,331,271 8,152,084 5,277,380 At December 31, 2018 the Group had tax losses to be carried forward of approximately £50,611,184 (2017: £36,010,916). Deferred tax Deferred tax relates to the following: December 31, 2016 2017 2018 (in £) Losses 2,778,396 6,121,400 8,603,902 Fixed assets (9,883 ) — 3,011 Other 2,210 — 2,888 Temporary differences trading — 2,266,798 494,779 Net deferred tax asset 2,770,723 8,388,198 9,104,580 The deferred tax asset has not been recognized as there is uncertainty regarding when suitable future profits against which to offset the accumulated tax losses will arise. There is no expiration date for the accumulated tax losses. A reduction in the rate of U.K. corporation tax to 19% from April 1, 2017 and to 17% from April 1, 2020 has been substantively enacted. The standard rate of corporation tax applied to reported loss is 19% (2017: 19.25%) and any U.K. deferred tax assets and liabilities would be recognized at a rate of 17%.

Loss per share

Loss per share	12 Months Ended
	Dec. 31, 2018
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Loss per share	10. 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 net losses from continuing operations were recorded in the year, the dilutive potential shares are anti-dilutive for the earnings per share calculation. December 31, 2016 2017 2018 Loss Weighted Loss per Loss Weighted Loss per Loss Weighted Loss per Basic and diluted (28,390,280 ) 44,789,893 (0.63 ) (38,799,054 ) 69,012,348 (0.56 ) (32,028,740 ) 71,144,786 (0.45 ) The Company operates share option schemes (see Note 25) which could potentially dilute basic earnings per share in the future. In addition, there exist within equity 864,988 (2017: 864,988) shares to be issued which also have the potential to dilute basic earnings per share in the future (see Note 17). 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 totalling 41,286 were issued in 2018 that could potentially dilute basic earnings per share if converted. Warrants totalling 696,490 were issued in 2017 that could potentially dilute basic earnings per share if converted. For transactions involving ordinary shares or potential ordinary shares between the reporting date and the date of authorization of these financial statements, see Note 29.

Property, plant and equipment

Property, plant and equipment	12 Months Ended
	Dec. 31, 2018
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Property, plant and equipment	11. Property, plant and equipment Leasehold Office IT Total (in £) Cost or valuation At January 1, 2016 155,494 20,024 40,360 215,878 Additions — — 3,467 3,467 Disposals — — (1,175 ) (1,175 ) At December 31, 2016 155,494 20,024 42,652 218,170 Depreciation and impairment At January 1, 2016 (5,625 ) (1,335 ) (4,401 ) (11,361 ) Disposals — — 457 457 Depreciation for the year (15,549 ) (4,005 ) (13,843 ) (33,397 ) At December 31, 2016 (21,174 ) (5,340 ) (17,787 ) (44,301 ) Net book value At January 1, 2016 149,869 18,689 35,959 204,517 At December 31, 2016 134,320 14,684 24,865 173,869 Cost or valuation At January 1, 2017 155,494 20,024 42,652 218,170 Additions — 10,107 5,461 15,568 Disposals — — — — At December 31, 2017 155,494 30,131 48,113 233,738 Depreciation and impairment At January 1, 2017 (21,174 ) (5,340 ) (17,787 ) (44,301 ) Disposals — — — — Depreciation for the year (15,549 ) (5,386 ) (15,141 ) (36,076 ) At December 31, 2017 (36,723 ) (10,726 ) (32,928 ) (80,377 ) Net book value At January 1, 2017 134,320 14,684 24,865 173,869 At December 31, 2017 118,771 19,405 15,185 153,361 Leasehold Office IT Total (in £) Cost or valuation At January 1, 2018 155,494 30,131 48,113 233,738 Additions 9,119 1,270 25,147 35,536 Disposals — — (2,167 ) (2,167 ) At December 31, 2018 164,613 31,401 71,093 267,107 Depreciation and impairment At January 1, 2018 (36,723 ) (10,726 ) (32,928 ) (80,377 ) Disposals — — 1,685 1,685 Depreciation for the year (15,909 ) (6,238 ) (17,334 (39,481 ) At December 31, 2018 52,632 16,964 48,577 118,173 Net book value At January 1, 2018 118,771 19,405 15,185 153,361 At December 31, 2018 111,981 14,437 22,516 148,934

Intangible assets

Intangible assets	12 Months Ended
	Dec. 31, 2018
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Intangible assets	12. Intangible assets Acquired (in £) Cost at January 1, 2016 25,812,941 Additions — At December 31, 2016 25,812,941 Amortization and impairment At January 1, 2016 — Impairment (Note 13) — At December 31, 2016 — Net book value At January 1, 2016 25,812,941 At December 31, 2016 25,812,941 Cost at January 1, 2017 25,812,941 Additions 7,192,288 At December 31, 2017 33,005,229 Amortization and impairment At January 1, 2017 — Impairment (Note 13) — At December 31, 2017 — Net book value At January 1, 2017 25,812,941 At December 31, 2017 33,005,229 Acquired (in £) Cost at January 1, 2018 and December 31, 2018 33,005,229 Amortization and impairment At January 1, 2018 — Revision to estimated value (373,000 ) At December 31, 2018 (373,000 ) Net book value At January 1, 2018 33,005,229 At December 31, 2018 32,632,229 The Group’s strategy is to acquire clinical-stage development programs for the treatment of non-rare On October 28, 2017, the Group acquired the exclusive license for MPH-966MPH-966 MPH-966 alpha-1 Year ended December 31, 2017 2018 (in £) Cash payment in October 2017 2,280,000 2,280,000 Equity issued (see Note 17) 1,520,000 1,520,000 Deferred equity consideration (see Note 25) 1,331,288 1,331,288 Present value of provision for deferred cash consideration (see Note 19) 2,061,000 1,688,000 7,192,288 6,819,288 The present value of the provision for deferred cash consideration was reviewed at December 31, 2018 (see Note 19). The decrease in present value due to changes in timelines and probability of contractual milestones being achieved was £373,000 and is recognized in the intangible asset in line with our accounting policies.

Impairment testing of acquired

Impairment testing of acquired development programs not yet available for use	12 Months Ended
	Dec. 31, 2018
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Impairment testing of acquired development programs not yet available for use	13. 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, 2017 (in £) BPS-804 MPH-9668 BGS-649 BCT-197 Total (setrusumab) (alvelestat) (leflutrozole) (acumapimod) Acquired development programs 11,615,824 7,192,288 9,886,356 4,310,761 33,005,229 Acquired development programs 11,615,824 6,819,288 9,886,356 4,310,761 32,632,229 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, 2018. The directors 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. The directors 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 the directors’ 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 At this stage of product development, the key sensitivity for all three 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, 2018
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Other receivables	14. Other receivables December 31, 2017 2018 (in £) Rent deposit 293,328 293,328 VAT recoverable 212,422 315,565 Cash held by Employee Benefit Trust 3,600 — 509,350 608,893

Cash and short-term deposits

Cash and short-term deposits	12 Months Ended
	Dec. 31, 2018
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Cash and short-term deposits	15. Cash and short-term deposits December 31, 2017 2018 (in £) Cash at banks and on hand 11,005,675 5,343,975 Short-term deposits 39,038,997 19,697,970 50,044,672 25,041,945 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, 2018
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Short-term investments	16. Short-term investments December 31, 2017 2018 (in £) Short-term investments 2,500,000 2,500,000 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, 2018
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Issued capital and reserves	17. Issued capital and reserves Ordinary share capital 2016 (in £) Balance at beginning of year 59,221 Issuances in the year 133,801 Nominal share capital as at December 31 193,022 Ordinary shares issued and fully paid At January 1, 2016 19,740,296 Issued on June 9, 2016 for private financing round 39,464,540 Issued on June 9. 2016 for private placement 5,135,962 At December 31, 2016 64,340,798 Nominal value at December 31, 2016 ( 0.003 Issued capital at December 31, 2016 ( 193,022 Ordinary share capital 2017 (in £) Balance at beginning of year 193,022 Issuances in the year 20,263 Nominal share capital as at December 31 213,285 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 (in £) Balance at beginning of year 213,285 Issuances in the year 436 Nominal share capital as at December 31 213,721 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 Since January 1, 2016, the following alterations to the Company’s share capital have been made: • under the subscription agreement dated July 28, 2015, as amended by an agreement dated June 1, 2016, the Company issued and allotted 39,464,540 ordinary shares of £0.003 in nominal value in the capital of the Company on June 9, 2016 at a price of £1.84 per share. 39,699 of these ordinary shares were issued to WG Partners LLP, for no cash consideration, as payment for financial advisory services; • 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 £7,000,000 and crediting a new Other reserve by the same amount; • under a private placement dated June 9, 2016, the Company issued and allotted 5,135,962 ordinary shares of £0.003 in nominal value in the capital of the Company on June 9, 2016 at a price of £2.21 per share; and • on June 9, 2016, the Company’s ordinary shares were admitted to trading on the AIM market of the London Stock Exchange. • 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; and • 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. December 31, Share premium 2016 (in £) At January 1, 2016 26,212,880 Share capital reduction on March 21, 2016 (7,000,000 ) Issuance of share capital for private financing round on June 9, 2016 72,423,314 Issuance of share capital for private placement on June 9, 2016 11,335,069 Transaction costs for issued share capital (2,995,864 ) At December 31, 2016 99,975,399 December 31, Share premium 2017 (in £) At January 1, 2017 99,975,399 Issued on April 3, 2017 for private placement financing round 14,984,875 Issued on April 26, 2017 for conversion of loan note 2,477,787 Issued on October 28, 2017 for acquisition of license 1,518,527 Transaction costs for issued share capital (729,632 ) At December 31, 2017 118,226,956 December 31, Share premium 2018 (in £) At January 1, 2018 118,226,956 Issued on June 1, 2018 for public offering 150,078 Issued on August 3, 2018 for exercise of share options 12,870 Issued on October 22, 2018 for exercise of share options 109,681 Transaction costs for issued share capital (7,512 ) At December 31, 2018 118,492,073 Other capital reserves Shares to Share-based Equity Total (in £) At January 1, 2016 18,677,840 2,982,265 — 21,660,105 Share-based payments expense during the year — 6,494,018 — 6,494,018 Shares issued (16,003,363 ) — — (16,003,363 ) Equity component of convertible loan instrument — — 516,802 516,802 At December 31, 2016 2,674,477 9,476,283 516,802 12,667,562 At January 1, 2017 2,674,477 9,476,283 516,802 12,667,562 Share-based payments expense during the year — 4,983,186 — 4,983,186 Shares issued (1,082,899 ) — — (1,082,899 ) Equity component of convertible loan instrument — — (208,680 ) (208,680 ) At December 31, 2017 1,591,578 14,459,469 308,122 16,359,169 Shares to Share-based Equity Warrants issued Total (in £) At January 1, 2018 1,591,578 14,459,469 308,122 — 16,359,169 Share-based payments expense during the year — 2,302,335 — — 2,302,335 Share-based payments release for exercise of options — (113,042 ) — — (113,042 ) Warrants issued for TAP funding — — — 44,156 44,156 At December 31, 2018 1,591,578 16,648,762 308,122 44,156 18,592,618 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 (see Note 25 for further details). 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 25 for further details of these plans. Of the £6,494,018 share-based payment expense in 2016, £298,836 is an accelerated charge relating to 500,000 share options which were cancelled on June 9, 2016. Shares issued/to be issued Shares to be issued at January 1, 2016 of £18,677,840 represented a maximum potential 10,151,000 bonus shares due to Novartis under the terms of an investment in the prior year. Of the 44,600,502 ordinary shares issued on June 9, 2016, 8,697,480 shares were issued to Novartis as fully paid up bonus shares (for £nil consideration), the number of which was calculated to maintain its shareholding at 19.5%. The fair value of these shares was £1.84 per share. At December 31, 2016, £2,674,477 representing a maximum of 1,453,520 shares at £1.84 were remaining to be issued to Novartis pro rata to their percentage shareholding as and when the Company issues further ordinary shares. Of the 1,221,361 ordinary shares issued on April 26, 2017, 588,532 shares were issued to Novartis as fully paid up bonus shares (for £nil consideration), the number of which was calculated to maintain its shareholding at 19.5%. The fair value of these shares was £1.84 per share. At December 31, 2018 and December 31, 2017, £1,591,578 representing a maximum of 864,988 shares at £1.84 were remaining to be issued to Novartis pro rata to its percentage shareholding as and when the Company issues further ordinary shares. Equity component of convertible loan instrument The convertible loan notes issued to Novartis are a compound instrument consisting of a liability and an equity component (see Note 18a). The value of the equity component (cost of the conversion option) as at December 31, 2018 is £308,122 (2017: £308,122; 2016: £516,802). Warrants issued for TAP funding The funding arrangements with The Alpha-1 Accumulated loss Year ended December 31 2016 2017 2018 (in £) Other reserves 7,000,000 7,000,000 7,000,000 Accumulated losses (40,579,241 ) (79,315,920 ) (111,220,794 ) Accumulated deficit (33,579,241 ) (72,315,920 ) (104,220,794 )

Interest-bearing loans and borr

Interest-bearing loans and borrowings	12 Months Ended
	Dec. 31, 2018
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Interest-bearing loans and borrowings	18. Interest-bearing loans and borrowings Year ended December 31 2017 2018 (in £) Novartis Notes – see Note 18a 1,977,393 2,038,881 Bank loan – see Note 18b 18,774,924 19,445,756 At December 31 20,752,317 21,484,637 Current 1,939,806 6,837,884 Non-current 18,812,511 14,646,753 18a. Convertible loan note On June 3, 2016, the Company issued 3,463,563 £1 unsecured convertible loan notes (“Novartis Notes”) to Novartis Pharma AG, a shareholder of the Company (see Note 26) in consideration for an investment in cash by Novartis at the time of the private placement on June 9, 2016. The Novartis Notes attract an interest rate of 4% per annum, accruing daily, and constitute direct, unsecured obligations of the Company ranking ahead of any other unsecured obligations of the Company. On April 26, 2017 Novartis converted £1,398,553 of loan notes into 632,829 ordinary shares at the fixed conversion price of £2.21 per share. This has been recorded as a £1,187,974 reduction in interest-bearing loans and borrowings, a reduction in other capital reserves of £208,680 and a reduction in accumulated losses of £62,375. Under the terms of the notes, Novartis also received 588,532 bonus shares. Novartis holds £2,065,011 principal value of notes at December 31, 2017 representing 934,394 ordinary shares if converted, together with 864,988 potential bonus shares; together these represent 2.5% of the current share capital of the Company as at December 31, 2017. In August 2017, in connection with the new loan agreements (see Note 18b), Novartis agreed to amend the terms of its Novartis Notes. Under the revised terms of the Novartis Notes, the loan is subordinated to the Silicon Valley Bank and Kreos Capital loan such that Novartis shall be entitled, at any time up to the repayment of the foregoing loan, being March 2, 2021, to serve a conversion notice on the Company to convert all or some only of the outstanding Novartis Notes into fully paid ordinary shares at a conversion price of £2.21 per share. To the extent the Novartis Notes are not converted at that date, the outstanding principal amount of the Novartis Notes, together with any accrued and unconverted interest, is redeemable. Upon conversion of any Novartis Notes, in addition to the relevant number of conversion shares, Novartis is entitled to receive an additional number of ordinary shares in the Company equal to the number of conversion shares into which such Novartis Notes are to convert, multiplied by 0.93, up to a maximum aggregate number of 864,988 such bonus shares. The value of the debt component of the notes at the date of issue was calculated as £2,946,761. The cash flows attached to the note up to the maturity date were calculated and discounted at an appropriate venture debt rate of 10%. The carrying amount at December 31, 2018 is £2,038,881 (2017: £1,977,393). The Group has applied IFRS 9 Financial Instruments in full without restating comparatives with an initial date of application of January 1, 2018 (see Note 2.2). The value of the equity component of the Notes at December 31, 2018 was calculated as £308,123 (2017: £308,123). 18b. Bank loan On August 7, 2017, the Group entered into a loan agreement with Silicon Valley Bank and Kreos Capital V (UK) Limited, which provides for total borrowings of £0 million and the issue of warrants over shares in the Company (see Note 20). £10.0 million was drawn down on each of August 21, 2017 (Tranche 1) and December 29, 2017 (Tranche 2) for general working capital purposes. The Group was obligated to make interest-only payments on the loan amount until September 30, 2018, and thereafter the Group was obligated to pay interest and principal in 30 equal monthly instalments until March 31, 2021, the maturity date. The loan bore interest at an annual fixed rate equal to 9.0%. In addition, a final payment of 7.5% of the principal loan amount was due upon the earlier of the maturity date, prepayment in whole of the loan amount, mandatory repayment, acceleration of the loan, and the loan becoming immediately due and payable due to an event of default. The loan was secured by substantially all of the Group’s assets, including intellectual property rights owned or controlled by the Group. The terms of the debt facility included an interest-only period to September 30, 2018, a 30-month The fair value of warrants issued as part of Tranche 1 on August 21, 2017 was £657,676. The fair value of the loan liability of Tranche 1 on August 21, 2017 was £9,342,324. Application of the effective interest method was required to accrete the initial loan liability value up to the face value of the loan at the end of the loan term. This non-cash The fair value of warrants issued as part of Tranche 2 on December 29, 2017 was £634,335. The fair value of the loan liability of Tranche 2 on December 29, 2017 was £9,365,665. Application of the effective interest method was required to accrete the initial loan liability value up to the face value of the loan at the end of the loan term. This non-cash On 30 September 2018 (the “modification date”), the Group and the lender signed a revised loan agreement (the “new loan”), with the intention that this would replace the old loan (with the proceeds of the new loan being used to settle the old loan). The new loan is viewed as a modification of the original loan because it was agreed with the same lenders as under the old loan and the old loan was not repayable at par with no penalty. The new loan has a principal amount of £20,455,000 and will mature on March 1, 2021, unless extended on reaching certain milestones. The Group is obligated to make interest-only payments on the loan amount until April 30, 2019, and thereafter the Group is obligated to pay interest and principal in 23 equal monthly instalments until March 31, 2021, the maturity date. The loan bears interest at an annual fixed rate equal to 8.5%. In addition, a final payment of 10.5% of the principal loan amount is due upon the earlier of the maturity date, prepayment in whole of the loan amount, mandatory repayment, acceleration of the loan, and the loan becoming immediately due and payable due to an event of default. The loan is secured by substantially all of the Group’s assets, including intellectual property rights owned or controlled by the Group. The terms of the debt facility include an interest-only period to April 30, 2019, a 23-month The modification loss is calculated as the difference in the present value of the cash flows under the original and modified terms. The modification loss has been calculated accordingly in the amount of £730,037 and has been recognized in profit and loss as of the date of the modification. The old loan was not derecognized; instead, at the point of modification, the carrying value of the loan was revised to reflect the new cash flows discounted by the original EIR as well as costs and fees incurred for the modification and any cash paid to or received from the lender under the terms of the new loan. Once the carrying amount of the liability was adjusted for costs and fees incurred as part of the modification, the EIR was recalculated to spread those costs and fees over the life of the modified liability. On the modification date, the Group issued 225,974 additional warrants (“additional warrants”), for nil consideration, to the lender with the same key terms as the original warrants. The fair value of the additional warrants as of their grant date (30 September 2018) was £375,343. The total carrying value of the loan at December 31, 2018 was £19,445,756 (2017: £18,774,924). £6,837,884 (2017: £1,939,806) is a current liability and £12,607,872 (2017: £16,835,118) is a non-current non-cash

Provisions

Provisions	12 Months Ended
	Dec. 31, 2018
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Provisions	19. Provisions Year ended December 31 2017 2018 (in £) Social security contributions on share options 2,288,386 842,367 Provision for deferred cash consideration 2,061,000 2,131,000 At December 31 4,349,386 2,973,367 Current 274,000 332,014 Non-current 4,075,386 2,641,353 Year ended December 31 Social security contributions on share options 2016 2017 2018 (in £) At beginning of year 141,311 1,172,420 2,288,386 Accretion of discount 7,293 — — Arising during the year 1,084,181 1,115,966 — Released (60,365 ) — (1,446,019 ) At December 31 1,172,420 2,288,386 842,367 Current — — — Non-current 1,172,420 2,288,386 842,367 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 gain arising on exercise of the share options, using the best estimate of the market price at the balance sheet date. Since the directors assume the options will be held for their full contractual life of ten years (see Note 25) the liability has been classified as non-current. Year ended December 31 Provisions for deferred cash consideration 2016 2017 2018 (in £) At beginning of year — — 2,061,000 Arising during the year — 2,061,000 — Increase in provision due to the unwinding of the time value of money — — 443,000 Decrease in provision due to a change in estimates relating to timelines and probabilities of contractual milestones being achieved (see Note 12) — — (373,000 ) At December 31 — 2,061,000 2,131,000 Current — 274,000 332,014 Non-current — 1,787,000 1,798,986 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 12). 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, 2018
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Warrant liability	20. Warrant liability Year ended December 31 2016 2017 2018 (in £) At beginning of year — — 1,346,484 Arising during the year — 1,292,011 375,343 Movement during the year — 54,473 (716,214 ) At December 31 — 1,346,484 1,005,613 As part of the bank loan facility (see Note 18b), 363,156 warrants to subscribe for shares were issued to the lenders on August 21, 2017. These warrants will be capable of exercise until August 7, 2027 at an exercise price of £3.029. A further 333,334 warrants were issued to the lenders on December 29, 2017. These warrants will be capable of exercise until August 7, 2027 at an exercise price of £3.30. A further 225,974 warrants were issued to the lenders on October 1, 2018. These warrants will be capable of exercise until October 1, 2028 at an exercise price of £2.31. The total of 922,464 warrants is equivalent to 1.30% of ordinary share capital at December 31, 2018. The terms of the warrant instrument allow for a cashless exercise. In line with IAS 32, the future number of shares to be issued to the warrant holder under a cashless exercise can only be determined at that future date. At each balance sheet date, the fair value of the warrants will be assessed using the Black Scholes model taking into account 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 2017 2018 (in £) Expected volatility (%) 50–51 65 Risk-free interest rate (%) 1.10–1.25 1.56 Expected life of share options (years) 9.6–10 10 Market price of ordinary shares (£) 3.00–3.25 2.31 Model used Black Scholes Black Scholes The fair value of the warrants at grant was £1,667,354. At December 31, 2018 it was £1,005,613 (2017: £1,346,484). 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, 2018
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Other liability	21. Other liability Year ended 2018 (in £) At beginning of year — Arising during the year 34,289 At December 31 34,289 On October 8, 2018, the Group entered into a funding agreement with The Alpha-1 MPH-966 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. The total carrying value of the liability at December 31, 2018 was £34,289. £34,289 is a non-current

Trade and other payables

Trade and other payables	12 Months Ended
	Dec. 31, 2018
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Trade and other payables	22. Trade and other payables Year ended December 31 2017 2018 (in £) Trade payables 2,860,303 4,392,602 Social security and other taxes 144,348 160,719 Other payables 19,375 16,986 At December 31 3,024,026 4,570,307 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, 2018
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Changes in liabilities arising from financing activities	23. Changes in liabilities arising from financing activities Bank loan Novartis Warrant Deferred TAP Total (in £) January 1, 2018 18,774,924 1,977,393 1,346,484 2,061,000 — 24,159,801 Cash Net increase in bank loan 455,000 — — — — 455,000 Increase in TAP funding — — — — 34,289 34,289 Interest payments (1,644,610 ) — — — — (1,644,610 ) Bank loan transaction costs (920,859 ) — — — — (920,859 ) Non-cash Bank modification loss 730,037 — — — — 730,037 Fair value of additional warrants (375,344 ) — — 70,000 — (305,344 ) Increase in warrant liability — — 375,344 — — 375,344 Novartis Notes - amounts restated through retained earnings — (123,864 ) — — — (123,864 ) Change in fair value warrant — — (716,215 ) — — (716,215 ) Provision for deferred cash consideration — — — — — — Interest accrual 1,644,610 — — — — 1,644,610 Accreted interest 781,998 185,352 — — — 967,350 December 31, 2018 19,445,756 2,038,881 1,005,613 2,131,000 34,289 24,655,539

Financial and capital risk mana

Financial and capital risk management and fair value measurement	12 Months Ended
	Dec. 31, 2018
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Financial and capital risk management and fair value measurement	24. Financial and capital risk management and fair value measurement 24.1. 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 17. The Group’s loans are disclosed in Note 18. 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 27). 24.2. 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. During the year, in order to maintain a strong cash runway the Group completed an equity placing and arranged and drew down a new bank debt facility, which includes an initial interest-only period until September 2018. Except for the bank loans and the existing convertible loan notes issued in 2016, 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, 2018. 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 both the convertible loan note and 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 Sterling, Euros and U.S. Dollars (USD). Funding to date has been secured in a mixture of Sterling and USD (in respect of funding attributable to the merger with OncoMed) 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, 2018 is the carrying amounts. The Group monitors its funding requirements through preparation of short-term, mid-term 24.3. Fair value hierarchy Fair value measurement using Date of valuation Total Quoted prices Significant Significant Liabilities measured at fair value Provision for deferred cash consideration (Note 19) December 31, 2018 £ 2,131,000 — — £ 2,131,000 Warrant liability (Note 20) December 31, 2018 £ 1,005,613 — — £ 1,005,613 Liabilities for which fair values are disclosed Convertible loan (Note 18a) December 31, 2018 £ 2,038,881 — — £ 2,038,881 Bank loan (Note 18b) December 31, 2018 £ 19,445,756 — — £ 19,445,756 TAP funding liability (Note 21) December 31, 2018 £ 34,829 — — £ 34,829 There were no transfers between Level 1 and Level 2 during 2018. Fair value measurement hierarchy for liabilities as at December 31, 2017: Fair value measurement using Date of valuation Total Quoted prices Significant Significant Liabilities measured at fair value Provision for deferred cash consideration (Note 19) December 31, 2017 £ 2,061,000 — — £ 2,061,000 Warrant liability (Note 20) December 31, 2017 £ 1,346,484 — — £ 1,346,484 Liabilities for which fair values are disclosed Convertible loan (Note 18a) December 31, 2017 £ 1,977,393 — — £ 1,977,393 Bank loan (Note 18b) December 31, 2017 £ 18,774,924 — — £ 18,774,924 There were no transfers between Level 1 and Level 2 during 2017. Set out below is a comparison, by class, of the carrying amounts and fair values of the Group’s financial instruments: December 31, 2017 December 31, 2018 Carrying Fair Carrying Fair (in £) Liabilities Provision for deferred cash consideration 2,061,000 2,061,000 2,131,000 2,131,000 Warrant liability 1,346,484 1,346,484 1,005,613 1,005,613 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 methods and assumptions were used to estimate the fair values: • 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. • The warrant liability is estimated using the 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. 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, 2018 and 2017 are as shown below: Valuation Significant Range Sensitivity of the input to fair value Provision for deferred cash consideration DCF WACC 2018: 15.3% 1% increase/(decrease) would result in a decrease/(increase) in fair value by £33,000. WACC 2017: 15.3% 1% increase/(decrease) would result in a decrease/(increase) in fair value by £30,000. Probability of 2018: 28%-95% 10% increase/(decrease) would result in an increase/(decrease) in fair value by £600,000. Probability of 2017: 28%-85% 10% increase/(decrease) would result in an increase/(decrease) in fair value by £600,000. Warrant liability Black Scholes Risk-free interest 2018: 1.33% 1% increase/(decrease) would result in an increase/(decrease) of £25,000 Risk-free interest 2017: 1.25% 1% increase/(decrease) would result in an increase/(decrease) of £46,000 Volatility 2018: 65% 10% increase/(decrease) would result in an increase/(decrease) of £145,000 Volatility 2017: 50% 10% increase/(decrease) would result in an increase/(decrease) of £200,000 Remaining life 2018: 3,254 days Increase/(decrease) of 365 days would result in an increase/(decrease) of £56,000 Remaining life 2017: 3,519 days Increase/(decrease) of 365 days would result in an increase/(decrease) of £54,000 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 (in £) Novartis Notes 82,600 2,161,642 — — 2,326,842 Bank loan 8,260,337 15,589,137 — — 23,849,474 Operating lease (see Note 26) 331,527 204,138 — — 535,665 8,674,464 17,954,917 — — 26,711,981 The table below summarizes our contractual obligations at December 31, 2017: Payments due by period Up to 1 year 1–3 years 3–5 years Over 5 years Total (in £) Novartis Notes 82,600 165,427 2,078,815 — 2,326,842 Bank loan 3,574,208 17,793,665 2,982,805 — 24,350,678 Operating lease (see Note 26) 743,858 535,203 — — 1,279,061 4,400,666 18,494,295 5,061,620 — 27,956,581 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

Share-based payments

Share-based payments	12 Months Ended
	Dec. 31, 2018
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Share-based payments	25. Share-based payments The charge for share-based payments under IFRS 2 arises across the following schemes: Year ended December 31, 2016 2017 2018 (in £) 2015 Plan 6,185,067 2,441,671 805,738 Mereo BioPharma Group plc Share Option Plan — 586,291 1,064,217 Long Term Incentive Plan 133,601 298,287 319,338 Deferred Bonus Share Plan 175,350 325,649 — 6,494,018 3,651,898 2,189,293 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. There are no performance conditions attached to the options issued under the Option Plan. 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, less a discount agreed with the Group’s institutional investors. The contractual term of the share options is ten years. Of the £6,185,067 expense recognized under the option plan for employee services received during 2016, £298,836 is an accelerated charge relating to 500,000 options which were cancelled on June 9, 2016. No share options were issued during the year under the 2015 Share 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: 2016 2017 2018 Number WAEP Number WAEP Number WAEP Outstanding at beginning of the year 8,964,394 1.29 9,198,655 1.32 9,124,610 1.32 Granted during the year 1,316,117 1.49 — — — — Cancelled during the year (500,000 ) 1.29 — — — — Forfeited during the year (581,856 ) 1.29 (74,045 ) 1.29 (46,255 ) 1.29 Exercised during the year — — — — (95,222 ) 1.29 Outstanding at December 31 9,198,655 1.32 9,124,610 1.32 8,983,133 1.32 Exercisable at December 31 3,115,337 1.29 5,655,676 1.31 8,007,029 1.31 The weighted average remaining contractual life for the share options outstanding as at December 31, 2018 was 6.6 years (2017: 7.6 years; 2016: 8.3 years). The weighted average fair value of options granted during 2016 was £1.29. There were no options granted in 2017. Options outstanding at the end of the year had an exercise price of between £1.29 and £2.21. The following tables list the weighted average inputs to the models used for the fair value of share options granted during the years ended December 31, 2016, 2017 and 2018: Year ended December 31 2016 2017 2018 (in £) Expected volatility (%) 56 — — Risk-free interest rate (%) 1.48-2.07 — — Expected life of share options (years) 10 — — Market price of ordinary shares (£) 1.84-2.21 — — Model used Black Schloes — — Since there is no historical data in relation to the expected life of the share options 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 share options. 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. With regard to an option which is subject to satisfaction of a performance condition, the option will normally vest on the later of: (i) the date on which our Board of directors determines that the performance condition has been satisfied; and (ii) the third anniversary of the date of grant. With regard to an option which is not subject to the satisfaction of a performance condition, the option will normally vest on the third anniversary of the date of grant, or such other date determined by our Board of directors and notified to the participant. Once an option has vested, it may be exercised during the period ending on the tenth anniversary of the date of grant, after which time it will lapse. The exercise price of an option may not be less than the greater of: (i) the market value of a share on the date of grant; or (ii) if the shares are to be subscribed, the nominal value of a share. Options are not currently subject to performance conditions other than continued service with us and typically vest on the third anniversary of the date of grant, after which they remain exercisable generally until the tenth anniversary of the grant date. Our Board of directors may determine that an option be settled in cash or by net exercise of the option. 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: 2016 2017 2018 Number WAEP Number WAEP Number WAEP Outstanding at beginning of the year — — — — 1,578,188 3.05 Granted during the year — — 1,193,188 3.05 388,000 3.14 Cancelled during the year — — — — — — Forfeited during the year — — (15,000 ) 3.03 (84,633 ) 3.03 Outstanding at December 31 — — 1,578,188 3.05 1,881,555 3.10 Exercisable at December 31 — — — — — — The weighted average remaining contractual life for the share options outstanding as at December 31, 2018 was 8.6 years (2017: 9.4 years). The weighted average fair value of options granted during the year was £2.29 (2017: £1.85). Options outstanding at the end of the year had an exercise price of between £2.76 and £3.23. The following tables list the weighted average inputs to the models used for the fair value of share options granted during the years ended December 31: Year ended December 31 2016 2017 2018 (in £) Expected volatility (%) — 49-51 65-67 Risk-free interest rate (%) — 1.06-1.33 1.39-1.53 Expected life of share options (years) — 10 10 Market price of ordinary shares (£) — 3.03-3.23 2.76-3.25 Model used — Black Scholes Black Scholes Since there is no historical data in relation to the expected life of the share options, 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 period equal to the expected life of the share options. 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 strategic targets. 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, 2018 was £319,338 (2017: £298,287). Movements during the year The following table illustrates the number of, and movements in, LTIP options during the year: 2016 Number 2017 2018 Granted during the year 1,199,658 185,950 — Cancelled during the year — — — Forfeited during the year (234,162 ) — — Outstanding at December 31 965,496 1,151,446 1,151,446 Exercisable at December 31 — — — The weighted average remaining contractual life for the LTIP options outstanding as at December 31, 2018 was 1.8 years (2017: 2.9 years; 2016: 3.7 years). The weighted average fair value of LTIP options granted during the year to December 31, 2018 was £nil (2017: £1.99; 2016: £1.21). 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: LTIP Share Price Element Year ended December 31 2016 2017 2018 Expected volatility (%) 48.9 51.7 — Risk-free interest rate (%) 0.48-0.74 0.17-0.39 — Expected life of share options (years) 3-5 3-5 — Market price of ordinary shares (£) 2.21 3.03 — Model used Monte Carlo Monte Carlo — LTIP Strategic Element Year ended December 31 2016 2017 2018 Expected volatility (%) 48.9 51.7 — Risk-free interest rate (%) 0.74 0.39 — Expected life of share options (years) 5 5 — Market price of ordinary shares (£) 2.21 3.03 — Model used Black Scholes 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. 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). The plan does allow for adjustment of awards in the event of a material misstatement of Mereo’s accounts or fraud or misconduct on the part of an individual. The plan also allows for adjustment of awards in the event there was an error in calculating the vesting of the awards. 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: 2016 Number 2017 2018 Outstanding at January 1 — 62,180 163,000 Awarded during the year 62,180 100,820 — Granted during the year — — — Outstanding at December 31 62,180 163,000 163,000 Exercisable at December 31 — — — The weighted average remaining contractual life for the DBSP options outstanding as at December 31, 2018 was 2.6 years (2017: 3.6 years; 2016: 4 years). The weighted average fair value of DBSP options granted during the year was £nil (2017: £3.23; 2016: £2.80). On January 18, 2019 the Board approved an amendment to the terms of the Deferred Bonus Share Plan and the terms were amended such that in the event that the Board decides to award a bonus to eligible participants in respect of performance for any given financial year, 30% of the bonus (after deduction of income tax and employee’s National Insurance contributions) must be used to purchase ordinary shares in the Company within 12 months. Following a purchase, the relevant ordinary shares must be held for a period of at least two years. Bonus awards made in respect of 2018 were awarded under these revised terms. The Mereo 2019 Equity Incentive Plan (The 2019 EIP) On April 4, 2019 the Company established The Mereo 2019 Equity Incentive Plan. Under the plan it is anticipated that market value options will be granted to executives and other employees with a four-year vesting period and no performance conditions. No grants have been made under this plan as at the date of this report. The plan provides a framework for the grant of market value options and/or restricted stock unit awards to officers of the Company (or of any subsidiary). The Mereo 2019 NED Equity Incentive Plan (The 2019 NED EIP) On April 4, 2019 the Company established The Mereo 2019 NED Equity Incentive Plan. Under the plan it is anticipated that market value options will be granted to non-executive non-executive one-year non-executive 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, being £3.10, giving a total of £1,331,288.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2018
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Commitments and contingencies	26. Commitments and contingencies Operating lease commitments – Group as lessee Future minimum rentals payable under non-cancellable Year ended December 31, 2017 2018 Within one year 743,858 331,527 After one year but not more than three years 535,203 204,138 After one year but not more than five years — — More than five years — — 1,279,061 535,665 The Group has entered into a lease for its premises at Fourth Floor, 1 Cavendish Place, London W1G 0QF. The term of the lease agreement is from August 17, 2015 through to August 16, 2025. The total lease expense for the year ended December 31, 2018 was £293,328 (2017: £293,328). The premises comprise approximately 4,000 sq ft. The principal rent for the premises is £162,960 per annum through December 16, 2016 and £325,920 per annum thereafter, subject to an increase on August 17, 2020 based on the open market value of the premises (the “Principal Rent”). In addition to the Principal Rent, the Group is responsible for value-added tax on the Principal Rent and certain insurance costs and service charges incurred by the landlord. The Group may break the lease agreement on August 16, 2020 by providing six months’ prior written notice to the landlord. If the Group does not exercise its break option, the landlord will decrease by 50% the Principal Rent for the period from August 16, 2020 through to April 15, 2021. The Group has entered into a lease for six high-resolution peripheral quantitative computed tomography (HRpQCT) scanners for use in its ongoing clinical studies. Each scanner has a lease term of 12 months from the date on which delivery of that scanner occurred. The Company has the right to extend the lease period for a further six months at any point during the lease term. This option may be exercised in respect of any of the individual scanners and does not have to be exercised in respect of all the scanners. Finance leases – Group as lessee The Group did not have any leasing arrangements classified as finance leases at December 31, 2018 (2017: £nil). 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 non-competition

Related party disclosures

Related party disclosures	12 Months Ended
	Dec. 31, 2018
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Related party disclosures	27. Related party disclosures The following transactions have been entered into with related parties for the year ended December 31, 2017 and 2018. Novartis Pharma AG (“Novartis”) holds shares in the Company at December 31, 2016. On June 3, 2016, the Group issued 3,463,563 £1 unsecured convertible loan notes (the “Novartis Notes”) to Novartis and received £3,463,563 from Novartis in consideration (Note 18a). The Group purchased goods and services from Novartis in the year as set out below: Year ended December 31, 2016 2017 2018 Manufacture and supply of clinical trial material 968,219 4,610,106 60,027 The amount outstanding to be paid to Novartis at December 31, 2018 was £nil (2017: £nil; 2016: £35,249). The purchases from related parties are made on terms equivalent to those that prevail in arm’s length transactions. Employee Benefit Trust In 2016 the Company set up an Employee Benefit Trust for the purposes of buying and selling shares on the employees’ behalf. A total of £325,000 of funding was paid into the Trust by the Company during the year ended December 31, 2018 (2017:£nil). A total of 163,000 shares were purchased by the Trust during the year ended December 31, 2018 (2017: nil). As at December 31, 2018 a cash balance of £21,762 (2017: £3,600) was held by the Trust.

Standards issued but not yet ef

Standards issued but not yet effective	12 Months Ended
	Dec. 31, 2018
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Standards issued but not yet effective	28. Standards issued but not yet effective The standards and interpretations that are issued, but not yet effective, up to the date of issuance of the Group’s financial statements are disclosed below. The Group intends to adopt these standards, if applicable, when they become effective. Other standards The following standards and interpretations, applicable for annual periods beginning on or after January 1, 2017, are not expected to have any impact on the results of the Group or the presentation of the financial statements: • IFRS 10 Consolidated Financial Statements – Amendments regarding the sale or contribution of assets between an investor and its associate or joint venture and amendments regarding the application of the consolidation exception. • IFRS 11 Joint Arrangements – Amendments regarding the accounting for acquisitions of an interest in a joint operation. • IFRS 12 Disclosure of Interests in Other Entities – Amendments regarding the application of the consolidation exception. • IFRS 14 Regulatory Deferral Accounts. • IAS 1 Presentation of Financial Statements – Amendments resulting from the disclosure initiative. • IAS 7 Statement of Cash Flows – Amendments resulting from the disclosure initiative. • IAS 12 Income Taxes – Amendments to recognition of deferred tax assets for unrealized losses. • IAS 16 Property, Plant and Equipment – Amendments regarding the clarification of acceptable methods of depreciation and amortization and amendments bringing bearer plants into the scope of IAS 16. • IAS 27 Separate Financial Statements (as amended in 2011) – Amendments reinstating the equity method as an accounting option for investments in subsidiaries, joint ventures and associates in an entity’s separate financial statements. • IAS 28 Investments in Associates and Joint Ventures – Amendments regarding the application of the consolidation exception. • IAS 38 Intangible Assets – Amendments regarding the clarification of acceptable methods of depreciation and amortization. • IAS 41 Agriculture – Amendments bringing bearer plants into the scope of IAS 16. • Amendments resulting from September 2014 Annual Improvements to IFRSs: • IFRS 2 Classification and Measurement of Share-based Payment Transactions. • IFRS 5 Non-current • IFRS 7 Financial Instruments: Disclosures. • IFRIC Interpretation 22 Foreign Currency Transactions and Advance Consideration. • IAS 19 Employee Benefits. • IAS 34 Interim Financial Reporting.

Event after the reporting perio

Event after the reporting period	12 Months Ended
	Dec. 31, 2018
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Event after the reporting period	29. Event after the reporting period (a) On February 8, 2019, Dr. Frank Armstrong resigned as a non-executive (b) On April 23, 2019 the Group agreed an amendment to the terms of its bank loan with the lenders. The new terms extended the interest-only period to December 31, 2019 followed by a 15-month non-substantial Following completion of the merger with OncoMed, under the terms of the loan agreement, Mereo expects to issue approximately 321,444 additional warrants to its lenders giving them the right to subscribe for ordinary shares at an exercise price of £2.95. (c) On April 23, 2019, Mereo completed the acquisition of OncoMed, a clinical-stage biopharmaceutical company whose shares were previously traded on NASDAQ. Mereo acquired 100% of the voting equity interests declared, and OncoMed will continue as a wholly-owned indirect subsidiary of Mereo. The Mereo Board believes that the combination of Mereo’s biopharmaceutical portfolio of four assets with OncoMed’s two lead assets will create a diversified combined portfolio, resulting in an increased number of potential near-term catalysts with a core focus remaining on Mereo’s strategy to target rare diseases, and that the cash position of the Combined Company will provide an extended operational runway, with the potential for such runway to be extended significantly further through partnering deals. The initial consideration for the purchase amounted to £40,892,478 in the form of 24,783,320 ordinary shares. The fair value of the ordinary shares issued was measured using the closing market price of Mereo’s ordinary shares at the acquisition date. Further amounts may be payable the former owners of OncoMed governed by the terms of an agreed Contingent Value Rights (CVR) agreement. The CVR represents the non-transferable OMP-313M32) OMP-305B83) The TIGIT milestone A payment, in the form of Mereo ADSs, will be made to CVR holders if, prior to December 31, 2019, the following milestone is achieved: • Celgene exercises the exclusive option granted by OncoMed to Celgene in relation to OncoMed’s OMP-313M32 • The receipt by OncoMed of the initial $35 million cash milestone payment due from Celgene pursuant to such Celgene option exercise. If the TIGIT milestone is achieved, holders of CVRs would be entitled to receive a number of Mereo ADSs equal to the $35 million cash milestone payment received net of any tax and other reasonable expenses, divided by the volume-weighted average price per Mereo ADS for the 10-trading The NAVI milestones A cash payment will be made to CVR holders if, within 18 months following the closing of the merger, Mereo or any of its subsidiaries enters into a definitive agreement with one or more third parties regarding the OMP-305B83 We have estimated that the fair value of the deferred consideration is immaterial and have not provided for any amount payable. We are finalizing the purchase price allocation and have determined a preliminary estimate of the fair value of the intangible assets acquired of £14.5 million. We acquired cash and cash equivalents, and short-term investments at completion of $50.8 million. We are finalizing the valuation of other assets and liabilities which will determine the amount of goodwill to be recognised. This will be disclosed in our interim financial statements for the period ending June 30, 2019.

Significant accounting polici_2

Significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2018
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Basis of preparation	2.1 Basis of preparation The Group’s annual financial statements have been prepared in accordance with International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). The financial information is presented in pounds sterling (“Sterling”).
Adoption of new accounting policies	2.2 Adoption of new accounting policies The following policies have been adopted since the start of the period: a) IFRS 9 Financial Instruments. In the current period the Group has applied IFRS 9 Financial Instruments (as revised in July 2014) and the related consequential amendments to other IFRS. IFRS 9 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 Interest-bearing loans and borrowings – convertible loan notes (in £) At January 1, 2018 calculated under IAS 39 1,977,393 Amounts restated through retained earnings (123,865 ) At January 1, 2018 under IFRS 9 1,853,528 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. b) IFRS 15 Revenue from Contracts with Customers In the current period the Group has adopted IFRS 15 Revenue from Contracts with Customers. The new revenue standard is applicable to all entities and will supersede all current revenue recognition requirements under IFRS. There has been no impact on Group reporting in the period. c) IFRS 16 Leases General impact of application of IFRS 16 Leases IFRS 16 provides a comprehensive model for the identification of lease arrangements and their treatment in the financial statements for both lessors and lessees. IFRS 16 will supersede the current lease guidance including IAS 17 Leases and the related Interpretations when it becomes effective for accounting periods beginning on or after January 1, 2019. The date of initial application of IFRS 16 for the Group will be January 1, 2019. The Group has chosen the modified retrospective application of IFRS 16 in accordance with IFRS 16:C5(b). Consequently, the Group will not restate the comparative information. In contrast to lessee accounting, IFRS 16 substantially carries forward the lessor accounting requirements in IAS 17. Impact of the new definition of a lease The Group will make use of the practical expedient available on transition to IFRS 16 not to reassess whether a contract is or contains a lease. Accordingly, the definition of a lease in accordance with IAS 17 and IFRIC 4 will continue to apply to those leases entered or modified before 1 January 2019. The change in definition of a lease mainly relates to the concept of control. IFRS 16 distinguishes between leases and service contracts on the basis of whether the use of an identified asset is controlled by the customer. Control is considered to exist if the customer has: • the right to obtain substantially all of the economic benefits from the use of an identified asset; and • the right to direct the use of that asset. The Group will apply the definition of a lease and related guidance set out in IFRS 16 to all lease contracts entered into or modified on or after January 1, 2019 (whether it is a lessor or a lessee in the lease contract). In preparation for the first-time application of IFRS 16, the Group has carried out an implementation project. The project has shown that the new definition in IFRS 16 will not change significantly the scope of contracts that meet the definition of a lease for the Group. Impact on lessee accounting IFRS 16 will change how the Group accounts for leases previously classified as operating leases under IAS 17, which were off-balance On initial application of IFRS 16, for all leases (except as noted below), the Group will: a) recognize right-of-use b) recognize depreciation of right-of-use c) separate the total amount of cash paid into a principal portion (presented within financing activities) and interest (presented within operating activities) in the consolidated cash flow statement. Lease incentives (e.g. rent-free period) will be recognized as part of the measurement of the right-of-use Under IFRS 16, right-of-use For short-term leases (lease term of 12 months or less) and leases of low-value As at December 31, 2018, the Group had non-cancellable The non-cancellable non-cancellable A preliminary assessment indicates that all of these arrangements relate to leases other than short-term leases and leases of low-value right-of-use right-to-use The preliminary assessment indicates that £nil of these arrangements relate to short-term leases and leases of low-value Under IAS 17, all lease payments on operating leases are presented as part of cash flows from operating activities. The impact of the changes under IFRS 16 to the 2019 statement of cash flows would be to reduce the cash used in operating activities by £932,268 and to increase net cash used in financing activities by the same amount.
Going concern	2.3 Going concern Though 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 research 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 by way of the completed merger with OncoMed (as described more fully in Note 29) 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.
Basis of consolidation	2.4 Basis of consolidation The consolidated financial information comprises the financial statements of Mereo BioPharma Group plc and its subsidiaries as at December 31, 2018. 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. All Group subsidiaries prepare yearly financial information to December 31 consistent with the Company.
Taxes	a) Taxes Current income tax Current income tax assets and liabilities are measured at the amount expected to be recovered from or paid to the taxation authorities, and include R&D tax credits receivable under the HM Revenue and Customs (HMRC) small or medium enterprise (SME) scheme, which provides additional taxation relief for qualifying expenditure on R&D activities, and allows for the surrender of tax losses in exchange for a cash payment from HMRC. Current income tax relating to items recognized directly in equity is recognized in equity and not in the statement of comprehensive loss. Income tax credit The Group benefits from the U.K. R&D tax credit regime whereby a portion of the Group’s losses can be surrendered for a cash rebate of up to 33.35% of eligible expenditures. Such credits are accounted for within the tax provision, in the year in which the expenditures were incurred. 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.
Foreign currencies	b) Foreign currencies The functional currency of the Company and its subsidiaries is Sterling. 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 profit or loss. Gains or losses on the retranslation of foreign currency balances at the year end are recognized in the consolidated statement of comprehensive loss under net foreign exchange gains/(losses).
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 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.
Leases	d) Leases Leases in which a significant portion of the risks and rewards of ownership are retained by the lessor are classified as operating leases. Payments made under operating leases (net of any incentives received from the lessor) are charged to the statement of comprehensive loss on a straight-line basis over the period of the lease. The Group leases its premises (see Note 26). The Company recognizes any lease incentives on a straight-line basis over the entire period of the lease, assuming that any break clauses available will not be exercised. By not exercising any break clauses, the Group receives a 50% rent discount from the landlord for a fixed period of time as described in Note 26. The determination of whether an arrangement is, or contains, a lease is based on the substance of the arrangement at the inception date. The arrangement is assessed for whether fulfilment of the arrangement is dependent on the use of a specific asset or assets or the arrangement conveys a right to use the asset or assets, even if that right is not explicitly specified in an arrangement.
Intangible assets	e) Intangible assets Intangible assets, relating to intellectual property rights acquired through licensing or assigning patents and know-how,
Fair value measurement	f) 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	g) Impairment of non-financial Further disclosures relating to impairment of non-financial • Disclosures for significant assumptions Note 3 • Property, plant and equipment Note 11 • Intangible assets not yet available for use Notes 12 and 13 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 (CGU) 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 CGU 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 CGU’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. Intangible assets not yet available for use are tested for impairment annually as at December 31 at the CGU level, as appropriate, and when circumstances indicate that the carrying value may be impaired. An impairment test was performed at December 31, 2018.
Cash and short-term deposits	h) 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	i) Short-term investments Cash on deposit for terms greater than three months are recognized at fair value in the balance sheet.
Provisions	j) Provisions General 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	k) Share-based payments Employees (including senior 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 the Share Option Plan. Executive officers are also provided with 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 excludes the impact of any non-market Under the 2015 Plan, options were historically awarded to employees, NEDs and certain consultants. Share options awarded to non-employees non-employee 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	l) Costs of issuing capital The Group deducts directly attributable costs of issuing capital from the proceeds in accordance with IAS 39 Financial Instruments: Recognition and Measurement. 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	m) 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, representing the embedded option to convert the liability into equity of the Group, is included in equity. An exchange between an existing borrower and lender of debt instruments with substantially different terms are accounted for as an extinguishment of the original financial liability and the recognition of a new financial liability as per IAS 39 and IFRS 9. Similarly, a substantial modification of the terms of an existing financial liability, or a part of it (whether or not due to the financial difficulty of the debtor) should be accounted for as an extinguishment of the original financial liability and the recognition of a new financial liability. In line with IAS 39 the terms of exchanged or modified debt are regarded as substantially different if the net present value of the cash flows under the new terms (including any fees paid net of any fees received) discounted at the original effective interest rate is at least 10% different from the discounted present value of the remaining cash flows of the original debt instrument. Where such modifications are less than 10% different, the effective interest rate is adjusted to take account of the new terms.
Employee Benefit Trust	n) Employee Benefit Trust The Group operates an Employee Benefit Trust (EBT): Mereo BioPharma Group plc Employee Benefit Trust. The EBT has been established to fulfil awards made under the Deferred Bonus Share Plan and the Long Term Incentive 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. In compliance with IAS 32 Financial Instruments: Presentation Group, shares held by the EBT are included in the consolidated balance sheet as a reduction in equity. Gains and losses on Group shares are recognized directly in equity. The Group consolidated accounts treat the EBT as an extension of the Group and the Company as it is controlled and therefore consolidated.
Research and development	o) Research and development 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
Provision for deferred cash consideration	p) 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	q) Bank loan and associated warrants After initial recognition, interest-bearing loans and borrowings are subsequently measured at amortized cost using the effective interest rate (EIR) method. The EIR amortization is included as a finance charge in the statement of comprehensive loss. This category applies to interest-bearing borrowings, trade and other payables. As the terms of the warrant instrument allow for a cashless exercise, in line with IAS 32 the associated warrants are measured at fair value with changes recorded through the statement of comprehensive loss (see Note 20). An exchange between an existing borrower and lender of debt instruments with substantially different terms are accounted for as an extinguishment of the original financial liability and the recognition of a new financial liability as per IAS 39 and IFRS 9. Similarly, a substantial modification of the terms of an existing financial liability, or a part of it, (whether or not due to the financial difficulty of the debtor) should be accounted for as an extinguishment of the original financial liability and the recognition of a new financial liability. In line with IAS 39 the terms of exchanged or modified debt are regarded as substantially different if the net present value of the cash flows under the new terms (including any fees paid net of any fees received) discounted at the original effective interest rate is at least 10% different from the discounted present value of the remaining cash flows of the original debt instrument. Where such modifications are less than 10% different, the effective interest rate is adjusted to take account of the new terms.
The Alpha-1 Project (TAP) funding agreement and associated warrants	r) The Alpha-1 The agreement is regarded as a compound instrument which includes both debt and equity components. As per IAS 32:31 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 re-measured,

Significant accounting polici_3

Significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Interest-Bearing Loans and Borrowings - Convertible Loan Notes	Interest-bearing loans and borrowings – convertible loan notes (in £) At January 1, 2018 calculated under IAS 39 1,977,393 Amounts restated through retained earnings (123,865 ) At January 1, 2018 under IFRS 9 1,853,528
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

Group information (Tables)

Group information (Tables)	12 Months Ended
	Dec. 31, 2018
Investments accounted for using equity method [abstract]
Summary of Information About Subsidiaries of the Group	The consolidated financial statements of the Group include: % equity interest December 31, Name Principal activities Country of incorporation 2017 2018 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 Mereo US Holdings Inc Holding U.S. — 100 Mereo MergerCo One Inc. Holding U.S. — 100 Mereo BioPharma Group plc Employee Benefit Trust Employee share scheme Jersey — —

Compensation of key managemen_2

Compensation of key management personnel of the Group (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Compensation Paid or Payable to Key Management	The compensation paid or payable to key management is set out below: Year ended December 31, 2016 2017 2018 (in £) Short-term benefits 2,111,712 2,756,979 3,176,168 Post-employment benefits 106,500 87,269 59,522 IFRS 2 share-based payment charge 4,631,853 2,726,337 1,470,025 Total compensation paid to key management personnel 6,850,065 5,570,585 4,705,715

Finance income and Finance ch_2

Finance income and Finance charge (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Finance Income	Finance income Year ended December 31 2016 2017 2018 (in £) Bank interest earned 374,906 826,855 306,831
Summary of Finance Costs	Finance charge Year ended December 31, 2016 2017 2018 (in £) Interest payable on convertible loan (179,765 ) (103,115 ) (185,352 ) Interest payable on bank loan — (327,123 ) (1,644,610 ) Accreted interest on bank loan — (66,935 ) (781,998 ) Transaction costs on bank loan — (200,000 ) — Loss on short-term deposits — (338,279 ) (21,903 ) Increase in provision for deferred cash consideration — — (443,000 ) Change in warrant fair value — (54,473 ) 716,214 Total finance charge (179,765 ) (1,089,925 ) (2,360,648 )

Employee benefits expense (Tabl

Employee benefits expense (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Employee Benefits Expense	December 31, 2016 2017 2018 (in £) Included in research and development expenses: Salaries 1,150,222 1,640,373 1,791,679 Social security costs (See Note 19) 344,467 420,417 (29,670 ) Pension contributions 50,864 77,425 73,401 Share-based payment expense 1,550,884 822,173 525,972 Included in administrative expenses: Salaries 2,132,920 2,253,393 2,902,759 Social security costs 1,040,409 1,159,548 (827,509 ) Pension contributions 109,187 96,598 97,962 Share-based payment expense 4,943,133 2,829,725 1,663,322 Total employee benefits expense 11,322,086 9,299,652 6,197,916

Income tax (Tables)

Income tax (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Income Tax Credit	Year ended December 31 2016 2017 2018 (in £) U.K. corporation tax R&D credit 5,331,271 8,152,084 5,277,380 Income tax credit 5,331,271 8,152,084 5,277,380
Summary of Reconciliation to the Earnings Loss Per Income Statement	The charge for the year can be reconciled to the loss per the income statement as follows: Year-ended December 31, 2016 2017 2018 (in £) Loss on ordinary activities before income tax (33,721,551 ) (46,951,138 ) (37,306,120 ) Loss on ordinary activities before tax at the U.K.’s statutory income tax rate of 19% (2017: 19.25%) 6,744,310 9,038,094 7,088,163 Expenses not deductible for tax purposes (permanent differences) (15,116 ) (14,316 ) (1,069,606 ) Temporary timing differences (1,300,044 ) (711,677 ) (276,881 ) R&D relief uplift 2,134,107 3,447,474 2,270,777 Losses (unrecognized) (2,231,986 ) (3,784,801 ) (2,803,796 ) Deferred income from MBG loan guarantee costs — 177,310 68,723 Tax credit for the year 5,331,271 8,152,084 5,277,380
Summary of Deferred Tax	Deferred tax relates to the following: December 31, 2016 2017 2018 (in £) Losses 2,778,396 6,121,400 8,603,902 Fixed assets (9,883 ) — 3,011 Other 2,210 — 2,888 Temporary differences trading — 2,266,798 494,779 Net deferred tax asset 2,770,723 8,388,198 9,104,580

Loss per share (Tables)

Loss per share (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Loss Per Share	December 31, 2016 2017 2018 Loss Weighted Loss per Loss Weighted Loss per Loss Weighted Loss per Basic and diluted (28,390,280 ) 44,789,893 (0.63 ) (38,799,054 ) 69,012,348 (0.56 ) (32,028,740 ) 71,144,786 (0.45 )

Property, plant and equipment (

Property, plant and equipment (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Property, Plant and Equipment	Leasehold Office IT Total (in £) Cost or valuation At January 1, 2016 155,494 20,024 40,360 215,878 Additions — — 3,467 3,467 Disposals — — (1,175 ) (1,175 ) At December 31, 2016 155,494 20,024 42,652 218,170 Depreciation and impairment At January 1, 2016 (5,625 ) (1,335 ) (4,401 ) (11,361 ) Disposals — — 457 457 Depreciation for the year (15,549 ) (4,005 ) (13,843 ) (33,397 ) At December 31, 2016 (21,174 ) (5,340 ) (17,787 ) (44,301 ) Net book value At January 1, 2016 149,869 18,689 35,959 204,517 At December 31, 2016 134,320 14,684 24,865 173,869 Cost or valuation At January 1, 2017 155,494 20,024 42,652 218,170 Additions — 10,107 5,461 15,568 Disposals — — — — At December 31, 2017 155,494 30,131 48,113 233,738 Depreciation and impairment At January 1, 2017 (21,174 ) (5,340 ) (17,787 ) (44,301 ) Disposals — — — — Depreciation for the year (15,549 ) (5,386 ) (15,141 ) (36,076 ) At December 31, 2017 (36,723 ) (10,726 ) (32,928 ) (80,377 ) Net book value At January 1, 2017 134,320 14,684 24,865 173,869 At December 31, 2017 118,771 19,405 15,185 153,361 Leasehold Office IT Total (in £) Cost or valuation At January 1, 2018 155,494 30,131 48,113 233,738 Additions 9,119 1,270 25,147 35,536 Disposals — — (2,167 ) (2,167 ) At December 31, 2018 164,613 31,401 71,093 267,107 Depreciation and impairment At January 1, 2018 (36,723 ) (10,726 ) (32,928 ) (80,377 ) Disposals — — 1,685 1,685 Depreciation for the year (15,909 ) (6,238 ) (17,334 (39,481 ) At December 31, 2018 52,632 16,964 48,577 118,173 Net book value At January 1, 2018 118,771 19,405 15,185 153,361 At December 31, 2018 111,981 14,437 22,516 148,934

Intangible assets (Tables)

Intangible assets (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Detailed Information about Intangible Assets	Acquired (in £) Cost at January 1, 2016 25,812,941 Additions — At December 31, 2016 25,812,941 Amortization and impairment At January 1, 2016 — Impairment (Note 13) — At December 31, 2016 — Net book value At January 1, 2016 25,812,941 At December 31, 2016 25,812,941 Cost at January 1, 2017 25,812,941 Additions 7,192,288 At December 31, 2017 33,005,229 Amortization and impairment At January 1, 2017 — Impairment (Note 13) — At December 31, 2017 — Net book value At January 1, 2017 25,812,941 At December 31, 2017 33,005,229 Acquired (in £) Cost at January 1, 2018 and December 31, 2018 33,005,229 Amortization and impairment At January 1, 2018 — Revision to estimated value (373,000 ) At December 31, 2018 (373,000 ) Net book value At January 1, 2018 33,005,229 At December 31, 2018 32,632,229
Summary of Intangible Assets Material to Entity	Year ended December 31, 2017 2018 (in £) Cash payment in October 2017 2,280,000 2,280,000 Equity issued (see Note 17) 1,520,000 1,520,000 Deferred equity consideration (see Note 25) 1,331,288 1,331,288 Present value of provision for deferred cash consideration (see Note 19) 2,061,000 1,688,000 7,192,288 6,819,288

Impairment testing of acquire_2

Impairment testing of acquired development programs not yet available for use (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Carrying Amount of Acquired Development Programs	The carrying amount of acquired development programs is as follows: As at December 31, 2017 (in £) BPS-804 MPH-9668 BGS-649 BCT-197 Total (setrusumab) (alvelestat) (leflutrozole) (acumapimod) Acquired development programs 11,615,824 7,192,288 9,886,356 4,310,761 33,005,229 Acquired development programs 11,615,824 6,819,288 9,886,356 4,310,761 32,632,229

Other receivables (Tables)

Other receivables (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Other Receivables	December 31, 2017 2018 (in £) Rent deposit 293,328 293,328 VAT recoverable 212,422 315,565 Cash held by Employee Benefit Trust 3,600 — 509,350 608,893

Cash and short-term deposits (T

Cash and short-term deposits (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Cash and Short-term Deposits	December 31, 2017 2018 (in £) Cash at banks and on hand 11,005,675 5,343,975 Short-term deposits 39,038,997 19,697,970 50,044,672 25,041,945

Short-term investments (Tables)

Short-term investments (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Short-term Investments	December 31, 2017 2018 (in £) Short-term investments 2,500,000 2,500,000

Issued capital and reserves (Ta

Issued capital and reserves (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Detailed Information of Ordinary Share Capital	Issued capital and reserves Ordinary share capital 2016 (in £) Balance at beginning of year 59,221 Issuances in the year 133,801 Nominal share capital as at December 31 193,022 Ordinary shares issued and fully paid At January 1, 2016 19,740,296 Issued on June 9, 2016 for private financing round 39,464,540 Issued on June 9. 2016 for private placement 5,135,962 At December 31, 2016 64,340,798 Nominal value at December 31, 2016 ( 0.003 Issued capital at December 31, 2016 ( 193,022 Ordinary share capital 2017 (in £) Balance at beginning of year 193,022 Issuances in the year 20,263 Nominal share capital as at December 31 213,285 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 (in £) Balance at beginning of year 213,285 Issuances in the year 436 Nominal share capital as at December 31 213,721 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
Summary of Share Premium	December 31, Share premium 2016 (in £) At January 1, 2016 26,212,880 Share capital reduction on March 21, 2016 (7,000,000 ) Issuance of share capital for private financing round on June 9, 2016 72,423,314 Issuance of share capital for private placement on June 9, 2016 11,335,069 Transaction costs for issued share capital (2,995,864 ) At December 31, 2016 99,975,399 December 31, Share premium 2017 (in £) At January 1, 2017 99,975,399 Issued on April 3, 2017 for private placement financing round 14,984,875 Issued on April 26, 2017 for conversion of loan note 2,477,787 Issued on October 28, 2017 for acquisition of license 1,518,527 Transaction costs for issued share capital (729,632 ) At December 31, 2017 118,226,956 December 31, Share premium 2018 (in £) At January 1, 2018 118,226,956 Issued on June 1, 2018 for public offering 150,078 Issued on August 3, 2018 for exercise of share options 12,870 Issued on October 22, 2018 for exercise of share options 109,681 Transaction costs for issued share capital (7,512 ) At December 31, 2018 118,492,073
Summary of Other Capital Reserves	Other capital reserves Shares to Share-based Equity Total (in £) At January 1, 2016 18,677,840 2,982,265 — 21,660,105 Share-based payments expense during the year — 6,494,018 — 6,494,018 Shares issued (16,003,363 ) — — (16,003,363 ) Equity component of convertible loan instrument — — 516,802 516,802 At December 31, 2016 2,674,477 9,476,283 516,802 12,667,562 At January 1, 2017 2,674,477 9,476,283 516,802 12,667,562 Share-based payments expense during the year — 4,983,186 — 4,983,186 Shares issued (1,082,899 ) — — (1,082,899 ) Equity component of convertible loan instrument — — (208,680 ) (208,680 ) At December 31, 2017 1,591,578 14,459,469 308,122 16,359,169 Shares to Share-based Equity Warrants issued Total (in £) At January 1, 2018 1,591,578 14,459,469 308,122 — 16,359,169 Share-based payments expense during the year — 2,302,335 — — 2,302,335 Share-based payments release for exercise of options — (113,042 ) — — (113,042 ) Warrants issued for TAP funding — — — 44,156 44,156 At December 31, 2018 1,591,578 16,648,762 308,122 44,156 18,592,618
Summary of Accumulated Loss	Year ended December 31 2016 2017 2018 (in £) Other reserves 7,000,000 7,000,000 7,000,000 Accumulated losses (40,579,241 ) (79,315,920 ) (111,220,794 ) Accumulated deficit (33,579,241 ) (72,315,920 ) (104,220,794 )

Interest-bearing loans and bo_2

Interest-bearing loans and borrowings (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Interest-bearing Loans and Borrowings	Year ended December 31 2017 2018 (in £) Novartis Notes – see Note 18a 1,977,393 2,038,881 Bank loan – see Note 18b 18,774,924 19,445,756 At December 31 20,752,317 21,484,637 Current 1,939,806 6,837,884 Non-current 18,812,511 14,646,753

Provisions (Tables)

Provisions (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Provisions	Year ended December 31 2017 2018 (in £) Social security contributions on share options 2,288,386 842,367 Provision for deferred cash consideration 2,061,000 2,131,000 At December 31 4,349,386 2,973,367 Current 274,000 332,014 Non-current 4,075,386 2,641,353
Summary of Social Security Contributions on Share Options	Year ended December 31 Social security contributions on share options 2016 2017 2018 (in £) At beginning of year 141,311 1,172,420 2,288,386 Accretion of discount 7,293 — — Arising during the year 1,084,181 1,115,966 — Released (60,365 ) — (1,446,019 ) At December 31 1,172,420 2,288,386 842,367 Current — — — Non-current 1,172,420 2,288,386 842,367
Summary of Provisions for Deferred Cash Consideration	Year ended December 31 Provisions for deferred cash consideration 2016 2017 2018 (in £) At beginning of year — — 2,061,000 Arising during the year — 2,061,000 — Increase in provision due to the unwinding of the time value of money — — 443,000 Decrease in provision due to a change in estimates relating to timelines and probabilities of contractual milestones being achieved (see Note 12) — — (373,000 ) At December 31 — 2,061,000 2,131,000 Current — 274,000 332,014 Non-current — 1,787,000 1,798,986

Warrant liability (Tables)

Warrant liability (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Warrant Liability	Year ended December 31 2016 2017 2018 (in £) At beginning of year — — 1,346,484 Arising during the year — 1,292,011 375,343 Movement during the year — 54,473 (716,214 ) At December 31 — 1,346,484 1,005,613
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 2017 2018 (in £) Expected volatility (%) 50–51 65 Risk-free interest rate (%) 1.10–1.25 1.56 Expected life of share options (years) 9.6–10 10 Market price of ordinary shares (£) 3.00–3.25 2.31 Model used Black Scholes Black Scholes

Other liability (Tables)

Other liability (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Other Liabilities	Year ended 2018 (in £) At beginning of year — Arising during the year 34,289 At December 31 34,289

Trade and other payables (Table

Trade and other payables (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Trade and Other Payables	Year ended December 31 2017 2018 (in £) Trade payables 2,860,303 4,392,602 Social security and other taxes 144,348 160,719 Other payables 19,375 16,986 At December 31 3,024,026 4,570,307

Changes in liabilities arisin_2

Changes in liabilities arising from financing activities (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Changes in Liabilities Arising from Financing Activities	Bank loan Novartis Warrant Deferred TAP Total (in £) January 1, 2018 18,774,924 1,977,393 1,346,484 2,061,000 — 24,159,801 Cash Net increase in bank loan 455,000 — — — — 455,000 Increase in TAP funding — — — — 34,289 34,289 Interest payments (1,644,610 ) — — — — (1,644,610 ) Bank loan transaction costs (920,859 ) — — — — (920,859 ) Non-cash Bank modification loss 730,037 — — — — 730,037 Fair value of additional warrants (375,344 ) — — 70,000 — (305,344 ) Increase in warrant liability — — 375,344 — — 375,344 Novartis Notes - amounts restated through retained earnings — (123,864 ) — — — (123,864 ) Change in fair value warrant — — (716,215 ) — — (716,215 ) Provision for deferred cash consideration — — — — — — Interest accrual 1,644,610 — — — — 1,644,610 Accreted interest 781,998 185,352 — — — 967,350 December 31, 2018 19,445,756 2,038,881 1,005,613 2,131,000 34,289 24,655,539

Financial and capital risk ma_2

Financial and capital risk management and fair value measurement (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Fair Value Hierarchy	24.3. Fair value hierarchy Fair value measurement using Date of valuation Total Quoted prices Significant Significant Liabilities measured at fair value Provision for deferred cash consideration (Note 19) December 31, 2018 £ 2,131,000 — — £ 2,131,000 Warrant liability (Note 20) December 31, 2018 £ 1,005,613 — — £ 1,005,613 Liabilities for which fair values are disclosed Convertible loan (Note 18a) December 31, 2018 £ 2,038,881 — — £ 2,038,881 Bank loan (Note 18b) December 31, 2018 £ 19,445,756 — — £ 19,445,756 TAP funding liability (Note 21) December 31, 2018 £ 34,829 — — £ 34,829 There were no transfers between Level 1 and Level 2 during 2018. Fair value measurement hierarchy for liabilities as at December 31, 2017: Fair value measurement using Date of valuation Total Quoted prices Significant Significant Liabilities measured at fair value Provision for deferred cash consideration (Note 19) December 31, 2017 £ 2,061,000 — — £ 2,061,000 Warrant liability (Note 20) December 31, 2017 £ 1,346,484 — — £ 1,346,484 Liabilities for which fair values are disclosed Convertible loan (Note 18a) December 31, 2017 £ 1,977,393 — — £ 1,977,393 Bank loan (Note 18b) December 31, 2017 £ 18,774,924 — — £ 18,774,924
Summary of Comparison, by Class, of the Carrying Amounts and Fair Values of Financial Instruments	Set out below is a comparison, by class, of the carrying amounts and fair values of the Group’s financial instruments: December 31, 2017 December 31, 2018 Carrying Fair Carrying Fair (in £) Liabilities Provision for deferred cash consideration 2,061,000 2,061,000 2,131,000 2,131,000 Warrant liability 1,346,484 1,346,484 1,005,613 1,005,613
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, 2018 and 2017 are as shown below: Valuation Significant Range Sensitivity of the input to fair value Provision for deferred cash consideration DCF WACC 2018: 15.3% 1% increase/(decrease) would result in a decrease/(increase) in fair value by £33,000. WACC 2017: 15.3% 1% increase/(decrease) would result in a decrease/(increase) in fair value by £30,000. Probability of 2018: 28%-95% 10% increase/(decrease) would result in an increase/(decrease) in fair value by £600,000. Probability of 2017: 28%-85% 10% increase/(decrease) would result in an increase/(decrease) in fair value by £600,000. Warrant liability Black Scholes Risk-free interest 2018: 1.33% 1% increase/(decrease) would result in an increase/(decrease) of £25,000 Risk-free interest 2017: 1.25% 1% increase/(decrease) would result in an increase/(decrease) of £46,000 Volatility 2018: 65% 10% increase/(decrease) would result in an increase/(decrease) of £145,000 Volatility 2017: 50% 10% increase/(decrease) would result in an increase/(decrease) of £200,000 Remaining life 2018: 3,254 days Increase/(decrease) of 365 days would result in an increase/(decrease) of £56,000 Remaining life 2017: 3,519 days Increase/(decrease) of 365 days would result in an increase/(decrease) of £54,000
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, 2018: Payments due by period Up to 1 year 1–3 years 3–5 years Over 5 years Total (in £) Novartis Notes 82,600 2,161,642 — — 2,326,842 Bank loan 8,260,337 15,589,137 — — 23,849,474 Operating lease (see Note 26) 331,527 204,138 — — 535,665 8,674,464 17,954,917 — — 26,711,981
Summary of Contractual Obligations	The table below summarizes our contractual obligations at December 31, 2017: Payments due by period Up to 1 year 1–3 years 3–5 years Over 5 years Total (in £) Novartis Notes 82,600 165,427 2,078,815 — 2,326,842 Bank loan 3,574,208 17,793,665 2,982,805 — 24,350,678 Operating lease (see Note 26) 743,858 535,203 — — 1,279,061 4,400,666 18,494,295 5,061,620 — 27,956,581

Share-based payments (Tables)

Share-based payments (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Charge for Share-based Payments Under IFRS 2	The charge for share-based payments under IFRS 2 arises across the following schemes: Year ended December 31, 2016 2017 2018 (in £) 2015 Plan 6,185,067 2,441,671 805,738 Mereo BioPharma Group plc Share Option Plan — 586,291 1,064,217 Long Term Incentive Plan 133,601 298,287 319,338 Deferred Bonus Share Plan 175,350 325,649 — 6,494,018 3,651,898 2,189,293
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: 2016 2017 2018 Number WAEP Number WAEP Number WAEP Outstanding at beginning of the year 8,964,394 1.29 9,198,655 1.32 9,124,610 1.32 Granted during the year 1,316,117 1.49 — — — — Cancelled during the year (500,000 ) 1.29 — — — — Forfeited during the year (581,856 ) 1.29 (74,045 ) 1.29 (46,255 ) 1.29 Exercised during the year — — — — (95,222 ) 1.29 Outstanding at December 31 9,198,655 1.32 9,124,610 1.32 8,983,133 1.32 Exercisable at December 31 3,115,337 1.29 5,655,676 1.31 8,007,029 1.31
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 years ended December 31, 2016, 2017 and 2018: Year ended December 31 2016 2017 2018 (in £) Expected volatility (%) 56 — — Risk-free interest rate (%) 1.48-2.07 — — Expected life of share options (years) 10 — — Market price of ordinary shares (£) 1.84-2.21 — — Model used Black Schloes — —
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: 2016 2017 2018 Number WAEP Number WAEP Number WAEP Outstanding at beginning of the year — — — — 1,578,188 3.05 Granted during the year — — 1,193,188 3.05 388,000 3.14 Cancelled during the year — — — — — — Forfeited during the year — — (15,000 ) 3.03 (84,633 ) 3.03 Outstanding at December 31 — — 1,578,188 3.05 1,881,555 3.10 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 years ended December 31: Year ended December 31 2016 2017 2018 (in £) Expected volatility (%) — 49-51 65-67 Risk-free interest rate (%) — 1.06-1.33 1.39-1.53 Expected life of share options (years) — 10 10 Market price of ordinary shares (£) — 3.03-3.23 2.76-3.25 Model used — Black Scholes Black Scholes
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: LTIP Share Price Element Year ended December 31 2016 2017 2018 Expected volatility (%) 48.9 51.7 — Risk-free interest rate (%) 0.48-0.74 0.17-0.39 — Expected life of share options (years) 3-5 3-5 — Market price of ordinary shares (£) 2.21 3.03 — Model used Monte Carlo Monte Carlo — LTIP Strategic Element Year ended December 31 2016 2017 2018 Expected volatility (%) 48.9 51.7 — Risk-free interest rate (%) 0.74 0.39 — Expected life of share options (years) 5 5 — Market price of ordinary shares (£) 2.21 3.03 — Model used Black Scholes Black Scholes —
Summary of Number and Movements in Long Term Incentive Plan Options	The following table illustrates the number of, and movements in, LTIP options during the year: 2016 Number 2017 2018 Granted during the year 1,199,658 185,950 — Cancelled during the year — — — Forfeited during the year (234,162 ) — — Outstanding at December 31 965,496 1,151,446 1,151,446 Exercisable at December 31 — — —
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: 2016 Number 2017 2018 Outstanding at January 1 — 62,180 163,000 Awarded during the year 62,180 100,820 — Granted during the year — — — Outstanding at December 31 62,180 163,000 163,000 Exercisable at December 31 — — —

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Future Minimum Lease Payments under Non-cancellable Operating Leases	Future minimum rentals payable under non-cancellable Year ended December 31, 2017 2018 Within one year 743,858 331,527 After one year but not more than three years 535,203 204,138 After one year but not more than five years — — More than five years — — 1,279,061 535,665

Related party disclosures (Tabl

Related party disclosures (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Purchased Goods and Services	The Group purchased goods and services from Novartis in the year as set out below: Year ended December 31, 2016 2017 2018 Manufacture and supply of clinical trial material 968,219 4,610,106 60,027

Significant Accounting Polici_4

Significant Accounting Policies - Summary of Interest-Bearing Loans and Borrowings - Convertible Loan Notes (Detail)	Jan. 01, 2018GBP (£)
Disclosure of financial liabilities at date of initial application of IFRS 9 [abstract]
At January 1, 2018 calculated under IAS 39	£ 1,977,393
Amounts restated through retained earnings	(123,865)
At January 1, 2018 under IFRS 9	£ 1,853,528

Significant Accounting Polici_5

Significant Accounting Policies - Additional Information (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of voluntary change in accounting policy [line items]
Non-cancellable operating lease commitments	£ 535,665	£ 1,279,061
Right-of-use asset	2,551,810
Lease liability	2,533,647
Lease liability incentives	32,090
Short-term leases and leases of low-value assets	0
Reduce in cash used in operating activities	(23,137,113)	(32,147,971)	£ (29,662,174)
Increase in net cash used in financing activities	£ (2,073,309)	£ 33,743,245	£ 68,356,519
Losses surrendered for cash rebate percentage of eligible expenditures	33.35%
Percentage of rent discount received from landlord	50.00%
Effective interest rate	10.00%
Increase (decrease) due to changes in accounting policy required by IFRSs [member]
Disclosure of voluntary change in accounting policy [line items]
Decrease in other expenses	£ (1,093,920)
Increase in depreciation	696,948
Increase in interest expense	322,662
Reduce in cash used in operating activities	(932,268)
Increase in net cash used in financing activities	£ 932,268

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, 2018
Leasehold improvements [member]
Disclosure of detailed information about property, plant and equipment [line items]
Estimated useful lives	ten years
Office equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Estimated useful lives	five years
IT equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Estimated useful lives	three years

Group Information - Summary of

Group Information - Summary of Information About Subsidiaries of the Group (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
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%
Mereo US Holdings Inc [member]
Disclosure of subsidiaries [line items]
Name	Mereo US Holdings Inc
Principal activities	Holding
Country of incorporation	U.S.
% equity interest	100.00%
Mereo MergerCo One Inc [member]
Disclosure of subsidiaries [line items]
Name	Mereo MergerCo One Inc.
Principal activities	Holding
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

Compensation of Key Managemen_3

Compensation of Key Management Personnel of the Group - Summary of Compensation Paid or Payable to Key Management (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of transactions between related parties [abstract]
Short-term benefits	£ 3,176,168	£ 2,756,979	£ 2,111,712
Post-employment benefits	59,522	87,269	106,500
IFRS 2 share-based payment charge	1,470,025	2,726,337	4,631,853
Total compensation paid to key management personnel	£ 4,705,715	£ 5,570,585	£ 6,850,065

Finance Income and Finance Ch_3

Finance Income and Finance Charge - Summary of Finance Income (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Material income and expense [abstract]
Bank interest earned	£ 306,831	£ 826,855	£ 374,906

Finance Income and Finance Ch_4

Finance Income and Finance Charge - Summary of Finance Costs (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Material income and expense [abstract]
Interest payable on convertible loan	£ (185,352)	£ (103,115)	£ (179,765)
Interest payable on bank loan	(1,644,610)	(327,123)
Accreted interest on bank loan	(781,998)	(66,935)
Transaction costs on bank loan		(200,000)
Loss on short-term deposits	(21,903)	(338,279)
Increase in provision for deferred cash consideration	(443,000)
Change in warrant fair value	716,214	(54,473)
Total finance charge	£ (2,360,648)	£ (1,089,925)	£ (179,765)

Employee Benefits Expense - Sum

Employee Benefits Expense - Summary of Employee Benefits Expense (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of employee benefits expense [line items]
Share-based payment expense	£ 2,189,293	£ 3,651,898	£ 6,494,018
Total employee benefits expense	6,197,916	9,299,652	11,322,086
Research and development expenses [member]
Disclosure of employee benefits expense [line items]
Salaries	1,791,679	1,640,373	1,150,222
Social security costs	(29,670)	420,417	344,467
Pension contributions	73,401	77,425	50,864
Share-based payment expense	525,972	822,173	1,550,884
Administrative expenses [member]
Disclosure of employee benefits expense [line items]
Salaries	2,902,759	2,253,393	2,132,920
Social security costs	(827,509)	1,159,548	1,040,409
Pension contributions	97,962	96,598	109,187
Share-based payment expense	£ 1,663,322	£ 2,829,725	£ 4,943,133

Income Tax - Summary of Income

Income Tax - Summary of Income Tax Credit (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Major components of tax expense (income) [abstract]
U.K. corporation tax R&D credit	£ 5,277,380	£ 8,152,084	£ 5,331,271
Income tax credit	£ 5,277,380	£ 8,152,084	£ 5,331,271

Income Tax - Summary of Reconci

Income Tax - Summary of Reconciliation to the Earnings Loss Per Income Statement (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Major components of tax expense (income) [abstract]
Loss on ordinary activities before income tax	£ (37,306,120)	£ (46,951,138)	£ (33,721,551)
Loss on ordinary activities before tax at the U.K.'s statutory income tax rate of 19% (2017: 19.25%)	7,088,163	9,038,094	6,744,310
Expenses not deductible for tax purposes (permanent differences)	(1,069,606)	(14,316)	(15,116)
Temporary timing differences	(276,881)	(711,677)	(1,300,044)
R&D relief uplift	2,270,777	3,447,474	2,134,107
Losses (unrecognized)	(2,803,796)	(3,784,801)	(2,231,986)
Deferred income from MBG loan guarantee costs	68,723	177,310
Tax credit for the year	£ 5,277,380	£ 8,152,084	£ 5,331,271

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, 2018	Dec. 31, 2017
Major components of tax expense (income) [abstract]
Statutory income tax rate	19.00%	19.25%

Income Tax - Additional Informa

Income Tax - Additional Information (Detail) - GBP (£)	Apr. 01, 2020	Apr. 01, 2017	Dec. 31, 2018	Dec. 31, 2017
Disclosure of income tax credit [line items]
Tax losses to be carried forward			£ 50,611,184	£ 36,010,916
Description of accumulated tax losses			The deferred tax asset has not been recognized as there is uncertainty regarding when suitable future profits against which to offset the accumulated tax losses will arise. There is no expiration date for the accumulated tax losses.
Description of corporate tax reduction			A reduction in the rate of U.K. corporation tax to 19% from April 1, 2017 and to 17% from April 1, 2020 has been substantively enacted.
Corporate tax reduction		19.00%
Standard rate of corporation tax applied to reported loss			19.00%	19.25%
Rate at which deferred tax assets and liabilities would be recognized			17.00%
Changes in tax rates or tax laws enacted or announced [member]
Disclosure of income tax credit [line items]
Corporate tax reduction	17.00%

Income Tax - Summary of Deferre

Income Tax - Summary of Deferred Tax (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset	£ 9,104,580	£ 8,388,198	£ 2,770,723
Losses [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset	8,603,902	6,121,400	2,778,396
Fixed assets [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset	3,011		(9,883)
Other [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset	2,888		£ 2,210
Temporary differences trading [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Net deferred tax asset	£ 494,779	£ 2,266,798

Loss per share - Summary of Los

Loss per share - Summary of Loss Per Share (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings per share [abstract]
Loss	£ (32,028,740)	£ (38,799,054)	£ (28,390,280)
Weighted shares number	71,144,786	69,012,348	44,789,893
Loss per share	£ (0.45)	£ (0.56)	£ (0.63)

Loss per share - Additional inf

Loss per share - Additional information (Detail) - shares	Apr. 26, 2017	Dec. 31, 2018	Dec. 31, 2017
Earnings per share [abstract]
Equity shares to be issued		864,988	864,988
New ordinary shares payable		1,349,692
Warrants issued	632,829	41,286	696,490

Property, Plant and Equipment -

Property, Plant and Equipment - Summary of Property, Plant and Equipment (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	£ 153,361	£ 173,869	£ 204,517
Ending balance	148,934	153,361	173,869
Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	233,738	218,170	215,878
Additions	35,536	15,568	3,467
Disposals	(2,167)		(1,175)
Ending balance	267,107	233,738	218,170
Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	(80,377)	(44,301)	(11,361)
Disposals	1,685		457
Depreciation for the year	(39,481)	(36,076)	(33,397)
Ending balance	118,173	(80,377)	(44,301)
Leasehold improvements [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	118,771	134,320	149,869
Ending balance	111,981	118,771	134,320
Leasehold improvements [member] | Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	155,494	155,494	155,494
Additions	9,119
Ending balance	164,613	155,494	155,494
Leasehold improvements [member] | Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	(36,723)	(21,174)	(5,625)
Depreciation for the year	(15,909)	(15,549)	(15,549)
Ending balance	52,632	(36,723)	(21,174)
Office equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	19,405	14,684	18,689
Ending balance	14,437	19,405	14,684
Office equipment [member] | Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	30,131	20,024	20,024
Additions	1,270	10,107
Ending balance	31,401	30,131	20,024
Office equipment [member] | Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	(10,726)	(5,340)	(1,335)
Depreciation for the year	(6,238)	(5,386)	(4,005)
Ending balance	16,964	(10,726)	(5,340)
IT equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	15,185	24,865	35,959
Ending balance	22,516	15,185	24,865
IT equipment [member] | Cost or valuation member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	48,113	42,652	40,360
Additions	25,147	5,461	3,467
Disposals	(2,167)		(1,175)
Ending balance	71,093	48,113	42,652
IT equipment [member] | Depreciation/Amortization and impairment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Beginning balance	(32,928)	(17,787)	(4,401)
Disposals	1,685		457
Depreciation for the year	(17,334)	(15,141)	(13,843)
Ending balance	£ 48,577	£ (32,928)	£ (17,787)

Intangible Assets - Summary of

Intangible Assets - Summary of Detailed Information about Intangible Assets (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of detailed information about intangible assets [line items]
Beginning balance	£ 33,005,229	£ 25,812,941	£ 25,812,941
Ending balance	32,632,229	33,005,229	25,812,941
Cost or valuation member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	33,005,229	25,812,941	25,812,941
Additions		7,192,288
Ending balance	33,005,229	33,005,229	25,812,941
Depreciation/Amortization and impairment [member]
Disclosure of detailed information about intangible assets [line items]
Revision to estimated value	(373,000)
Impairment		£ 0	£ 0
Ending balance	£ (373,000)

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - GBP (£)	Oct. 28, 2017	Dec. 31, 2018	Dec. 31, 2017
Cost or valuation member]
Disclosure of detailed information about intangible assets [line items]
Additions			£ 7,192,288
Cost or valuation member] | MPH-9668 [member]
Disclosure of detailed information about intangible assets [line items]
Additions	£ 7,192,288
Depreciation/Amortization and impairment [member]
Disclosure of detailed information about intangible assets [line items]
Revision to estimated value		£ 373,000

Intangible Assets - Summary o_2

Intangible Assets - Summary of Intangible Assets Material to Entity (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of detailed information about intangible assets [line items]
Cash payment		£ 2,280,000
Equity issued			£ 67,888,821
Deferred equity consideration			£ 6,494,018
Present value of provision for deferred cash consideration	£ 443,000
Total	32,632,229	33,005,229
MPH-9668 [member]
Disclosure of detailed information about intangible assets [line items]
Cash payment	2,280,000	2,280,000
Equity issued	1,520,000	1,520,000
Deferred equity consideration	1,331,288	1,331,288
Present value of provision for deferred cash consideration	1,688,000	2,061,000
Total	£ 6,819,288	£ 7,192,288

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 (£)	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	£ 32,632,229	£ 33,005,229
BPS-804 [member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	11,615,824	11,615,824
MPH-9668 [member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	6,819,288	7,192,288
BGS-649 [member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	9,886,356	9,886,356
BCT-197 [member]
Disclosure of detailed information about intangible assets [line items]
Acquired development programs	£ 4,310,761	£ 4,310,761

Impairment Testing of Acquire_4

Impairment Testing of Acquired Development Programs Not Yet Available for Use - Additional Information (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
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 (£)	Dec. 31, 2018	Dec. 31, 2017
Disclosure of other receivables [abstract]
Rent deposit	£ 293,328	£ 293,328
VAT recoverable	315,565	212,422
Cash held by Employee Benefit Trust		3,600
Total	£ 608,893	£ 509,350

Cash and Short-term Deposits -

Cash and Short-term Deposits - Summary of Cash and Short-term Deposits (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and cash equivalents [abstract]
Cash at banks and on hand	£ 5,343,975	£ 11,005,675
Short-term deposits	19,697,970	39,038,997
Total	£ 25,041,945	£ 50,044,672	£ 53,577,571	£ 12,247,986

Short-term Investments - Summar

Short-term Investments - Summary of Short-term Investments (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017
Short- Term Investments [abstract]
Short-term investments	£ 2,500,000	£ 2,500,000

Issued Capital and Reserves - S

Issued Capital and Reserves - Summary of Detailed Information of Ordinary Share Capital (Detail) - GBP (£)	Oct. 22, 2018	Aug. 03, 2018	Jun. 01, 2018	Oct. 28, 2017	Apr. 26, 2017	Apr. 03, 2017	Jun. 09, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2017	Jun. 01, 2016
Disclosure of classes of share capital [line items]
Beginning balance								£ 62,483,490	£ 79,256,742	£ 62,483,490
Issuances in the year										67,888,821
Ending balance								32,770,780	62,483,490	79,256,742
Nominal value					£ 0.003
Ordinary shares [member]
Disclosure of classes of share capital [line items]
Beginning balance								213,285	193,022	59,221
Issuances in the year								436	20,263	133,801
Ending balance								£ 213,721	£ 213,285	£ 193,022
Ordinary shares issued and fully paid, Beginning balance								71,094,974	64,340,798	19,740,296
Ordinary shares issued and fully paid, Ending balance								71,240,272	71,094,974	64,340,798
Nominal value	£ 0.003	£ 0.003	£ 0.003			£ 0.003		£ 0.003	£ 0.003	£ 0.003	£ 0.003	£ 0.003
Ordinary shares [member] | Private financing round [member]
Disclosure of classes of share capital [line items]
Issued						5,042,017	39,464,540
Ordinary shares [member] | Private placement [member]
Disclosure of classes of share capital [line items]
Issued							5,135,962
Nominal value							£ 0.003
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 [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

Issued Capital and Reserves - A

Issued Capital and Reserves - Additional Information (Detail)	Jun. 01, 2018GBP (£)£ / sharesshares	Apr. 26, 2017GBP (£)£ / sharesshares	Apr. 03, 2017GBP (£)£ / sharesshares	Dec. 31, 2016GBP (£)£ / sharesshares	Jun. 09, 2016GBP (£)£ / sharesshares	Jun. 01, 2016GBP (£)£ / sharesshares	Mar. 21, 2016GBP (£)	Dec. 31, 2018GBP (£)£ / sharesshares	Dec. 31, 2017GBP (£)£ / sharesshares	Dec. 31, 2016GBP (£)£ / sharesshares	Oct. 22, 2018£ / sharesshares	Aug. 03, 2018£ / sharesshares	Oct. 31, 2017£ / sharesshares	Jan. 01, 2016shares	Dec. 31, 2015shares
Disclosure of classes of share capital [line items]
Nominal value | £ / shares		£ 0.003
Conversion of loan notes into ordinary shares amount | £		£ 1,398,552
Conversion of loan notes into ordinary shares		632,829						41,286	696,490
Share conversion price per share | £ / shares		£ 2.21
Bonus shares received		588,532
Share-based payments - share options | £										£ 6,494,018
Employee services accelerated charge | £										£ 298,836
Share options cancelled										500,000
Share options cancelled date										Jun. 9, 2016
Equity component (consideration received for the warrants) | £				£ 0				£ 44,156	£ 0	£ 0
Directors [member]
Disclosure of classes of share capital [line items]
Reduction in share premium | £							£ 7,000,000
Novartis [member]
Disclosure of classes of share capital [line items]
Equity component (cost of the conversion option) | £				£ 516,802				£ 308,122	£ 308,122	£ 516,802
Ordinary shares [member]
Disclosure of classes of share capital [line items]
Ordinary shares issued and allotted	50,076	1,221,361	5,042,017		44,600,502	39,464,540					85,222	10,000	490,798	18,677,840
Nominal value | £ / shares	£ 0.003		£ 0.003	£ 0.003		£ 0.003		£ 0.003	£ 0.003	£ 0.003	£ 0.003	£ 0.003	£ 0.003
Ordinary shares price per share | £ / shares	£ 3		£ 2.975			£ 1.84
Cash consideration | £	£ 150,228		£ 15,000,000
Shares issued as fully paid up				64,340,798				71,240,272	71,094,974	64,340,798					19,740,296
Ordinary shares [member] | Private placement [member]
Disclosure of classes of share capital [line items]
Ordinary shares issued and allotted					5,135,962
Nominal value | £ / shares					£ 0.003
Ordinary shares price per share | £ / shares					2.21
Ordinary shares [member] | WG Partners LLP [member]
Disclosure of classes of share capital [line items]
Ordinary shares issued and allotted						39,699
Cash consideration | £						£ 0
Ordinary shares [member] | Novartis [member]
Disclosure of classes of share capital [line items]
Ordinary shares issued and allotted				2,674,477				1,591,578	1,591,578	2,674,477
Maximum shares to be issued				1,453,520				864,988	864,988	1,453,520
Ordinary shares to be issued price per share | £ / shares				£ 1.84				£ 1.84	£ 1.84
Novartis bonus shares [member]
Disclosure of classes of share capital [line items]
Ordinary shares price per share | £ / shares					£ 1.84			£ 1.84
Cash consideration | £					£ 0			£ 0
Maximum shares to be issued														10,151,000
Shares issued as fully paid up					8,697,480			588,532
Shareholding percentage					19.50%			19.50%

Issued Capital and Reserves -_2

Issued Capital and Reserves - Summary of Share Premium (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of classes of share capital [line items]
Beginning balance	£ 118,226,956
Ending balance	118,492,073	£ 118,226,956
Share premium [member]
Disclosure of classes of share capital [line items]
Beginning balance	118,226,956	99,975,399	£ 26,212,880
Share capital reduction on March 21, 2016			(7,000,000)
Issued on April 3, 2017 for private placement financing round		14,984,875
Issued on June 1, 2018 for public offering	150,078
Issuance of share capital for private financing round on June 9, 2016			72,423,314
Issued on April 26, 2017 for conversion of loan note		2,477,787
Issuance of share capital for private placement on June 9, 2016			11,335,069
Issued on October 28, 2017 for acquisition of license		1,518,527
Transaction costs for issued share capital	(7,512)	(729,632)	(2,995,864)
Ending balance	118,492,073	£ 118,226,956	£ 99,975,399
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	12,870
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	£ 109,681

Issued Capital and Reserves -_3

Issued Capital and Reserves - Summary of Other Capital Reserves (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of classes of share capital [line items]
Beginning balance	£ 7,000,000	£ 7,000,000
Share-based payments expense during the year			£ 6,494,018
Shares issued			67,888,821
Equity component of convertible loan instrument		62,375
Ending balance	7,000,000	7,000,000	7,000,000
Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	16,359,169	12,667,562	21,660,105
Share-based payments expense during the year	2,302,335	4,983,186	6,494,018
Share-based payments release for exercise of options	(113,042)
Shares issued		(1,082,899)	(16,003,363)
Warrants issued for TAP funding	44,156
Equity component of convertible loan instrument		(208,680)	516,802
Ending balance	18,592,618	16,359,169	12,667,562
Shares to be issued [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	1,591,578	2,674,477	18,677,840
Shares issued		(1,082,899)	(16,003,363)
Ending balance	1,591,578	1,591,578	2,674,477
Share-based payments [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	14,459,469	9,476,283	2,982,265
Share-based payments expense during the year	2,302,335	4,983,186	6,494,018
Share-based payments release for exercise of options	(113,042)
Ending balance	16,648,762	14,459,469	9,476,283
Equity component of convertible loan [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Beginning balance	308,122	516,802
Equity component of convertible loan instrument		(208,680)	516,802
Ending balance	308,122	£ 308,122	£ 516,802
Warrants issued for TAP funding [member] | Capital reserve [member]
Disclosure of classes of share capital [line items]
Warrants issued for TAP funding	44,156
Ending balance	£ 44,156

Issued Capital and Reserves -_4

Issued Capital and Reserves - Summary of Accumulated Loss (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of classes of share capital [abstract]
Other reserves	£ 7,000,000	£ 7,000,000	£ 7,000,000
Accumulated losses	(111,220,794)	(79,315,920)	(40,579,241)
Accumulated deficit	£ (104,220,794)	£ (72,315,920)	£ (33,579,241)

Interest-bearing Loans and Bo_3

Interest-bearing Loans and Borrowings - Summary of Interest-bearing Loans and Borrowings (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about borrowings [abstract]
Novartis Notes	£ 2,038,881	£ 1,977,393
Bank loan	19,445,756	18,774,924
Interest-bearing loans and borrowings	21,484,637	20,752,317
Current	6,837,884	1,939,806
Non-current	14,646,753	18,812,511
Interest-bearing loans and borrowings	£ 21,484,637	£ 20,752,317

Interest-bearing Loans and Bo_4

Interest-bearing Loans and Borrowings - Additional Information (Detail)	Nov. 16, 2018GBP (£)	Sep. 30, 2018GBP (£)Installmentshares	Aug. 07, 2017GBP (£)Installment	Apr. 26, 2017GBP (£)£ / sharesshares	Jun. 03, 2016£ / sharesshares	Dec. 31, 2018GBP (£)shares	Dec. 31, 2017GBP (£)shares	Aug. 17, 2017£ / shares
Disclosure of detailed information about borrowings [line items]
Issue of warrants over shares	£ 44,156					£ 44,156
Effective interest rate						10.00%
Interest-bearing loans and borrowings , Current						£ 6,837,884	£ 1,939,806
Interest-bearing loans and borrowings , Non current						14,646,753	18,812,511
Accreted interest on bank loan						781,998	66,935
Bank loan [member]
Disclosure of detailed information about borrowings [line items]
borrowing interest rate		8.50%	9.00%
Notes issued value			£ 0
Interest-bearing loans and borrowings						19,445,756	18,774,924
Notional amount			£ 0
Number of monthly installments | Installment		23	30
Loan maturity date		March 1, 2021	March 31, 2021
Issue of warrants over shares			£ 10,000,000
Interest rate on loans		8.50%	9.00%
Percentage of principal amount due		10.50%	7.50%
Headline interest rate		8.50%	9.00%
Principal amount		£ 20,455,000
Loan amount payable date		Apr. 30, 2019
Losses on borrowings recognized in profit and loss		£ 730,037
Number of additional warrants | shares		225,974
Fair value of additional warrants		£ 375,343
Interest-bearing loans and borrowings						19,445,756	18,774,924
Interest-bearing loans and borrowings , Current						6,837,884	1,939,806
Interest-bearing loans and borrowings , Non current						£ 12,607,872	£ 16,835,118
Bank loan [member] | August 21, 2017 Tranche 1 [member]
Disclosure of detailed information about borrowings [line items]
Fair value of warrants issued			£ 657,676
Fair value of loan liability			9,342,324
Annual value of this interest charge			£ 182,133
Effective interest rate			1.95%
Bank loan [member] | December 29, 2017 Tranche 2 [member]
Disclosure of detailed information about borrowings [line items]
Fair value of warrants issued			£ 634,335
Fair value of loan liability			9,365,665
Annual value of this interest charge			£ 194,892
Effective interest rate			2.08%
Novartis Pharma AG [member]
Disclosure of detailed information about borrowings [line items]
Issuance of unsecured convertible loan notes | shares					3,463,563
Share price per share | £ / shares					£ 1
borrowing interest rate					4.00%
Headline interest rate					4.00%
Novartis [member]
Disclosure of detailed information about borrowings [line items]
Convertible loan amount				£ 1,398,553
Number of converted loans converted to ordinary shares | shares				632,829			934,394
Conversion price per share | £ / shares				£ 2.21				£ 2.21
Reduction in interest-bearing loans and borrowings				£ 1,187,974
Reduction in other capital reserves				208,680
Reduction in accumulated losses				£ 62,375
Bonus shares | shares				588,532		864,988	864,988
Principal value convertible loans							£ 2,065,011
Percentage of current share capital							2.50%
Conversion price ratio						93.00%
Notes issued value						£ 2,946,761
Discounted debt ratio percentage						10.00%
Interest-bearing loans and borrowings						£ 2,038,881	£ 1,977,393
Equity component of the Notes						308,123	308,123
Notional amount						2,946,761
Interest-bearing loans and borrowings						£ 2,038,881	£ 1,977,393

Provisions - Summary of Provisi

Provisions - Summary of Provisions (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of other provisions [line items]
Provisions	£ 2,973,367	£ 4,349,386
Current	332,014	274,000
Non-current	2,641,353	4,075,386
Social security contributions on share options [member]
Disclosure of other provisions [line items]
Provisions	842,367	2,288,386	£ 1,172,420	£ 141,311
Current	0	0	0
Non-current	842,367	2,288,386	£ 1,172,420
Provision for deferred cash consideration [member]
Disclosure of other provisions [line items]
Provisions	2,131,000	2,061,000
Current	332,014	274,000
Non-current	£ 1,798,986	£ 1,787,000

Provisions - Summary of Social

Provisions - Summary of Social Security Contributions on Share Options (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of other provisions [line items]
Beginning balance	£ 4,349,386
Ending balance	2,973,367	£ 4,349,386
Current	332,014	274,000
Non-current	2,641,353	4,075,386
Social security contributions on share options [member]
Disclosure of other provisions [line items]
Beginning balance	2,288,386	1,172,420	£ 141,311
Accretion of discount			7,293
Arising during the year		1,115,966	1,084,181
Released	(1,446,019)		(60,365)
Ending balance	842,367	2,288,386	1,172,420
Current	0	0	0
Non-current	£ 842,367	£ 2,288,386	£ 1,172,420

Provisions - Summary of Provi_2

Provisions - Summary of Provisions for Deferred Cash Consideration (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of other provisions [line items]
Beginning balance	£ 4,349,386
Ending balance	2,973,367	£ 4,349,386
Current	332,014	274,000
Non-current	2,641,353	4,075,386
Provision for deferred cash consideration [member]
Disclosure of other provisions [line items]
Beginning balance	2,061,000
Arising during the year		2,061,000
Increase in provision due to the unwinding of the time value of money	443,000
Decrease in provision due to a change in estimates relating to timelines and probabilities of contractual milestones being achieved (see Note 12)	(373,000)
Ending balance	2,131,000	2,061,000
Current	332,014	274,000
Non-current	£ 1,798,986	£ 1,787,000

Warrant Liability - Summary of

Warrant Liability - Summary of Warrant Liability (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of classes of share capital [abstract]
Beginning balance	£ 1,346,484
Arising during the year	375,343	£ 1,292,011
Movement during the year	(716,214)	54,473
Ending balance	£ 1,005,613	£ 1,346,484

Warrant Liability - Additional

Warrant Liability - Additional Information (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of classes of share capital [line items]
Warrants issued	922,464
Percentage of ordinary share capital	1.30%
Fair value of warrants granted during prior period	£ 1,667,354
Fair value of the warrants at grant	£ 1,005,613	£ 1,346,484
Warrants issued on August 21, 2017 [member]
Disclosure of classes of share capital [line items]
Warrants issued	363,156
Exercise price	£ 3.029
Exercise date	Aug. 7, 2027
Warrants issued on December 29, 2017 [member]
Disclosure of classes of share capital [line items]
Warrants issued	333,334
Exercise price	£ 3.30
Exercise date	Aug. 7, 2027
Warrants issued on October 1, 2018 [member]
Disclosure of classes of share capital [line items]
Warrants issued	225,974
Exercise price	£ 2.31
Exercise date	Oct. 1, 2028

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] - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of classes of share capital [line items]
Expected volatility	65.00%
Risk-free interest rate	1.56%
Expected life of share options (years)	10 years
Market price of ordinary shares	£ 2.31
Model used	Black Scholes
Bottom of range [member]
Disclosure of classes of share capital [line items]
Expected volatility		50.00%
Risk-free interest rate		1.10%
Expected life of share options (years)		9 years 7 months 6 days
Market price of ordinary shares		£ 3
Model used		Black Scholes
Top of range [member]
Disclosure of classes of share capital [line items]
Expected volatility		51.00%
Risk-free interest rate		1.25%
Expected life of share options (years)		10 years
Market price of ordinary shares		£ 3.25

Other Liability - Summary of Ot

Other Liability - Summary of Other Liabilities (Detail)	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure Of Other Liabilities [abstract]
Beginning balance	£ 0
Arising during the year	34,289
Ending balance	£ 34,289

Other Liability - Additional In

Other Liability - Additional Information (Detail)	Nov. 16, 2018GBP (£)	Dec. 31, 2018GBP (£)	Nov. 16, 2018USD ($)	Oct. 08, 2018USD ($)	Dec. 31, 2017GBP (£)
Disclosure Of Other Liabilities [line items]
Payments 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	£ 44,156
Carrying value of other liability		34,289			£ 0
Carrying value of other non current liability		£ 34,289
MPH-966 [member]
Disclosure Of Other Liabilities [line items]
Payments from TAP agreement | $				$ 400,000

Trade and Other Payables - Summ

Trade and Other Payables - Summary of Trade and Other Payables (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017
Trade and other payables [abstract]
Trade payables	£ 4,392,602	£ 2,860,303
Social security and other taxes	160,719	144,348
Other payables	16,986	19,375
At December 31	£ 4,570,307	£ 3,024,026

Changes in Liabilities Arisin_3

Changes in Liabilities Arising from Financing Activities - Summary of Changes in Liabilities Arising from Financing Activities (Detail)	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	£ 24,159,801
Net increase in bank loan	455,000
Increase in TAP funding	34,289
Interest payments	(1,644,610)
Bank loan transaction costs	(920,859)
Bank modification loss	730,037
Fair value of additional warrants	(305,344)
Increase in warrant liability	375,344
Novartis Notes - amounts restated through retained earnings	(123,864)
Change in fair value warrant	(716,215)
Provision for deferred cash consideration	0
Interest accrual	1,644,610
Accreted interest	967,350
Ending balance	24,655,539
Bank loan [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	18,774,924
Net increase in bank loan	455,000
Interest payments	(1,644,610)
Bank loan transaction costs	(920,859)
Bank modification loss	730,037
Fair value of additional warrants	(375,344)
Provision for deferred cash consideration	0
Interest accrual	1,644,610
Accreted interest	781,998
Ending balance	19,445,756
Novartis notes [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	1,977,393
Novartis Notes - amounts restated through retained earnings	(123,864)
Provision for deferred cash consideration	0
Accreted interest	185,352
Ending balance	2,038,881
Warrant liability [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	1,346,484
Increase in warrant liability	375,344
Change in fair value warrant	(716,215)
Provision for deferred cash consideration	0
Ending balance	1,005,613
deffered cash consideration [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning balance	2,061,000
Fair value of additional warrants	70,000
Provision for deferred cash consideration	0
Ending balance	2,131,000
TAP agreement [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Increase in TAP funding	34,289
Provision for deferred cash consideration	0
Ending balance	£ 34,289

Financial and Capital Risk Ma_3

Financial and Capital Risk Management and Fair Value Measurement - Additional Information (Detail) - Credit risk [member]	Dec. 31, 2018GBP (£)
Investment counterparties [member]
Disclosure of detailed information about financial instruments [line items]
Exposure risk	£ 10,000,000
Cash deposit counterparties [member]
Disclosure of detailed information about financial instruments [line items]
Exposure risk	£ 5,000,000

Financial and Capital Risk Ma_4

Financial and Capital Risk Management and Fair Value Measurement - Summary of Fair Value Hierarchy (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Provision for deferred cash consideration [member]
Disclosure of fair value measurement of liabilities [line items]
Date of valuation	Dec. 31, 2018	Dec. 31, 2017
Financial liabilities at fair value	£ 2,131,000	£ 2,061,000
Financial liabilities	£ 2,131,000	£ 2,061,000
Warrant liability [member]
Disclosure of fair value measurement of liabilities [line items]
Date of valuation	Dec. 31, 2018	Dec. 31, 2017
Financial liabilities at fair value	£ 1,005,613	£ 1,346,484
Financial liabilities	£ 1,005,613	£ 1,346,484
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	Dec. 31, 2017
Financial liabilities	£ 2,038,881	£ 1,977,393
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, 2018	Dec. 31, 2017
Financial liabilities	£ 19,445,756	£ 18,774,924
The Alpha-1 Project funding 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, 2018
Financial liabilities	£ 34,829
Level 3 of fair value hierarchy [member] | Provision for deferred cash consideration [member]
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities at fair value	2,131,000	2,061,000
Level 3 of fair value hierarchy [member] | Warrant liability [member]
Disclosure of fair value measurement of liabilities [line items]
Financial liabilities at fair value	1,005,613	1,346,484
Level 3 of fair value hierarchy [member] | 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	2,038,881	1,977,393
Level 3 of fair value hierarchy [member] | 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	19,445,756	£ 18,774,924
Level 3 of fair value hierarchy [member] | The Alpha-1 Project funding 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	£ 34,829

Financial and Capital Risk Ma_5

Financial and Capital Risk Management and Fair Value Measurement - Summary of Comparison, by Class, of the Carrying Amounts and Fair Values of Financial Instruments (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017
Provision for deferred cash consideration [member]
Disclosure of detailed information about financial instruments [line items]
Carrying amount	£ 2,131,000	£ 2,061,000
Fair value	2,131,000	2,061,000
Warrant liability [member]
Disclosure of detailed information about financial instruments [line items]
Carrying amount	1,005,613	1,346,484
Fair value	£ 1,005,613	£ 1,346,484

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) - Quantitative Sensitivity analysis [member] - Level 3 of fair value hierarchy [member] - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
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	£ 33,000	£ 30,000
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	£ 600,000	£ 600,000
Risk-free interest rates [member] | Warrant liability [member] | Black And Scholes Method [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Risk-free interest rate	1.33%	1.25%
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	£ 25,000	£ 46,000
Volatility [member] | Warrant liability [member] | Black And Scholes Method [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Volatility	65.00%	50.00%
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	£ 145,000	£ 200,000
Remaining Life [member] | Warrant liability [member] | Black And Scholes Method [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Remaining life of increase decrease in sensitivity analysis affecting input to fair value	365 days	365 days
Remaining life	3254 days	3519 days
Increase decrease in sensitivity analysis affecting input to fair value	£ 56,000	£ 54,000
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	28.00%	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)	Dec. 31, 2018GBP (£)
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	£ 26,711,981
Novartis notes [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	2,326,842
Bank loan [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	23,849,474
Operating lease [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	535,665
Within one year [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	8,674,464
Within one year [member] | Novartis notes [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	82,600
Within one year [member] | Bank loan [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	8,260,337
Within one year [member] | Operating lease [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	331,527
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	17,954,917
After one year but not more than three years [member] | Novartis notes [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	2,161,642
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	15,589,137
After one year but not more than three years [member] | Operating lease [member]
Disclosure of maturity analysis for non-derivative financial liabilities [line items]
Financial liabilities on contractual undiscounted payments	£ 204,138

Financial and Capital Risk Ma_8

Financial and Capital Risk Management and Fair Value Measurement - Summary of Contractual Obligations (Detail)	Dec. 31, 2017GBP (£)
Disclosure Of Contractual Obligations [line items]
Contractual obligations	£ 27,956,581
Novartis notes [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	2,326,842
Bank loan [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	24,350,678
Operating lease [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	1,279,061
Within one year [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	4,400,666
Within one year [member] | Novartis notes [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	82,600
Within one year [member] | Bank loan [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	3,574,208
Within one year [member] | Operating lease [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	743,858
After one year but not more than three years [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	18,494,295
After one year but not more than three years [member] | Novartis notes [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	165,427
After one year but not more than three years [member] | Bank loan [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	17,793,665
After one year but not more than three years [member] | Operating lease [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	535,203
After one year but not more than five years [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	5,061,620
After one year but not more than five years [member] | Novartis notes [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	2,078,815
After one year but not more than five years [member] | Bank loan [member]
Disclosure Of Contractual Obligations [line items]
Contractual obligations	£ 2,982,805

Share-based Payments - Charge f

Share-based Payments - Charge for Share-based Payments Under IFRS 2 (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	£ 2,189,293	£ 3,651,898	£ 6,494,018
2015 Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	805,738	2,441,671	6,185,067
Mereo BioPharma Group plc Share Option Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	1,064,217	586,291
Long-term incentive plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments	£ 319,338	298,287	133,601
Deferred bonus share plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments		£ 325,649	£ 175,350

Share-based Payments - Addition

Share-based Payments - Additional Information (Detail)	Apr. 04, 2019	Jan. 18, 2019	Oct. 31, 2017GBP (£)shares	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)	Dec. 31, 2016GBP (£)
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share-based payments - share options						£ 6,494,018
Employee services accelerated charge						£ 298,836
Share options cancelled						500,000
Share options cancelled date						Jun. 9, 2016
Number of shares granted, but not yet paid | shares			429,448
Fair value of ordinary shares			£ 3.10
Amount of shares granted | shares			1,331,288
2015 Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Contractual term share options				10 years
Share-based payments - share options						£ 6,185,067
Employee services accelerated charge						£ 298,836
Share options cancelled						500,000
Share options cancelled date				Jun. 9, 2016
Number of options granted				0		1,316,117
Weighted average remaining contractual life for the share options outstanding period				6 years 7 months 6 days	7 years 7 months 6 days	8 years 3 months 18 days
Weighted average fair value of options granted					£ 0	£ 1.29
Contractual term				10 years
Weighted average share price of options granted						£ 1.49
2015 Plan [member] | Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options outstanding exercise price				£ 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					£ 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	1,193,188
Weighted average remaining contractual life for the share options outstanding period				8 years 7 months 6 days	9 years 4 months 24 days
Weighted average fair value of options granted				£ 2.29	£ 1.85
Options outstanding exercise price				2.76	3.23
Weighted average share price of options granted				£ 3.14	£ 3.05
Long-term incentive plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Contractual term share options				5 years
Number of options granted					185,950	1,199,658
Weighted average remaining contractual life for the share options outstanding period				1 year 9 months 18 days	2 years 10 months 24 days	3 years 8 months 12 days
Weighted average fair value of options granted				£ 0	£ 1.99	£ 1.21
Percentage of options issued to employees				75.00%
Percentage of options vested to employees				25.00%
Vesting period				5 years
Contractual term				5 years
Employee services expense				£ 319,338	£ 298,287
Deferred bonus share plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options granted				0	0	0
Annual bonus payable in deferred shares				30.00%
Weighted average remaining contract term (in years)				0	0	0
Weighted average share price of options granted				£ 0	£ 3.23	£ 2.80
Share-based compensation arrangement by share-based payment award, percent of annual bonus for purchasing ordinary shares		3000.00%
Mereo Two Thousand And Nineteen Equity Incentive Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options granted	0
Vesting period	Four-year
Mereo Two Thousand And Nineteen NED Equity incentive Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options granted	0
Mereo Two Thousand And Nineteen NED Equity incentive Plan [member] | Existing Non-Executive Directors [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Vesting period	One-year
Mereo Two Thousand And Nineteen NED Equity incentive Plan [member] | Newly Non-Executive Directors [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Vesting period	Three-year
AstraZeneca [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share issued upon consideration | shares			1,349,693

Share-based Payments - Summary

Share-based Payments - Summary of Number and Weighted Average Exercise Prices (WAEP) of, and Movements in, Options (Detail)	12 Months Ended
	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)	Dec. 31, 2016GBP (£)
2015 Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options outstanding at beginning of the year	9,124,610	9,198,655	8,964,394
Number of options granted during the year	0		1,316,117
Number of options cancelled during the year			500,000
Number of options forfeited during the year	(46,255)	(74,045)	(581,856)
Number of options exercised during the year	(95,222)
Number of options outstanding at December 31	8,983,133	9,124,610	9,198,655
Number of options exercisable at December 31	8,007,029	5,655,676	3,115,337
WAEP options outstanding at beginning of the year	£ 1.32	£ 1.32	£ 1.29
WAEP options granted during the year			1.49
WAEP options cancelled during the year			1.29
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	£ 1.31	£ 1.31	£ 1.29
Mereo BioPharma Group plc Share Option Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options outstanding at beginning of the year	1,578,188
Number of options granted during the year	388,000	1,193,188
Number of options forfeited during the year	(84,633)	(15,000)
Number of options outstanding at December 31	1,881,555	1,578,188
WAEP options outstanding at beginning of the year	£ 3.05
WAEP options granted during the year	3.14	£ 3.05
WAEP options forfeited during the year	3.03	3.03
WAEP options outstanding at December 31	£ 3.10	£ 3.05

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) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long-term incentive plan [member] | Monte carlo option pricing model [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)		51.70%	48.90%
Market price of ordinary shares (£)		£ 3.03	£ 2.21
Model used	-	Monte Carlo	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%	48.90%
Risk-free interest rate (%)		0.39%	0.74%
Expected life of share options (years)		5 years	5 years
Market price of ordinary shares (£)		£ 3.03	£ 2.21
Model used	-	Black Scholes	Black Scholes
2015 Plan [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)			56.00%
Expected life of share options (years)			10 years
Model used	-	-	Black Schloes
Mereo BioPharma Group plc Share Option Plan [member]
Disclosure of classes of share capital [line items]
Expected life of share options (years)	10 years	10 years
Model used	Black Scholes	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%	0.48%
Expected life of share options (years)		3 years	3 years
Bottom of range [member] | 2015 Plan [member]
Disclosure of classes of share capital [line items]
Risk-free interest rate (%)			1.48%
Market price of ordinary shares (£)			£ 1.84
Bottom of range [member] | Mereo BioPharma Group plc Share Option Plan [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)	65.00%	49.00%
Risk-free interest rate (%)	1.39%	1.06%
Market price of ordinary shares (£)	£ 2.76	£ 3.03
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%	0.74%
Expected life of share options (years)		5 years	5 years
Top of range [member] | 2015 Plan [member]
Disclosure of classes of share capital [line items]
Risk-free interest rate (%)			2.07%
Market price of ordinary shares (£)			£ 2.21
Top of range [member] | Mereo BioPharma Group plc Share Option Plan [member]
Disclosure of classes of share capital [line items]
Expected volatility (%)	67.00%	51.00%
Risk-free interest rate (%)	1.53%	1.33%
Market price of ordinary shares (£)	£ 3.25	£ 3.23

Share-based Payments - Summar_3

Share-based Payments - Summary of Number and Movements in Long Term Incentive Plan Options (Detail) - Long-term incentive plan [member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [line items]
Granted during the year		185,950	1,199,658
Cancelled during the year	0	0	0
Forfeited during the year			(234,162)
Number of options outstanding at December 31	1,151,446	1,151,446	965,496
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) - Deferred bonus share plan [member]	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options outstanding at beginning of the year	163,000	62,180
Awarded during the year		100,820	62,180
Granted during the year	0	0	0
Number of options outstanding at December 31	163,000	163,000	62,180
Exercisable at December 31	0	0	0

Commitments and Contingencies -

Commitments and Contingencies - Summary of Future Minimum Lease Payments under Non-cancellable Operating Leases (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017
Disclosure of finance lease and operating lease by lessee [line items]
Non cancellable operating leases	£ 535,665	£ 1,279,061
Within one year [member]
Disclosure of finance lease and operating lease by lessee [line items]
Non cancellable operating leases	331,527	743,858
After one year but not more than three years [member]
Disclosure of finance lease and operating lease by lessee [line items]
Non cancellable operating leases	£ 204,138	£ 535,203

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Detail) $ in Millions	1 Months Ended		12 Months Ended
	Aug. 16, 2020	Oct. 31, 2017USD ($)shares	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)	Dec. 16, 2017GBP (£)	Dec. 16, 2016GBP (£)
Disclosure of commitments and contingencies [line items]
Lease expense | £			£ 293,328	£ 293,328
Principal rent for the premises | £					£ 325,920	£ 162,960
Lease term			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
Subsequent Event [member]
Disclosure of commitments and contingencies [line items]
Percentage of decrease of principal rent	50.00%

Related Party Disclosures - Add

Related Party Disclosures - Additional Information (Detail) - GBP (£)	Jun. 03, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of transactions between related parties [line items]
Amount outstanding		£ 0	£ 0	£ 35,249
Amount paid to trust by the company		£ 325,000	£ 0
Shares purchased by the trust		163,000	0
Cash balance held by the trust		£ 21,762	£ 3,600
Novartis Pharma AG [member]
Disclosure of transactions between related parties [line items]
Convertible loan issued	3,463,563
Share price per share	£ 1
Cash consideration received	£ 3,463,563

Related Party Disclosures - Sum

Related Party Disclosures - Summary of Purchased Goods and Services (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of transactions between related parties [abstract]
Manufacture and supply of clinical trial material	£ 60,027	£ 4,610,106	£ 968,219

Event After the Reporting Per_2

Event After the Reporting Period - Additional Information (Detail) - Major business combination [member] $ in Millions	Apr. 23, 2019GBP (£)shares	Dec. 31, 2018USD ($)	Dec. 31, 2019GBP (£)	Dec. 31, 2018GBP (£)
NAVI milestones [member]
Disclosure of non-adjusting events after reporting period [line items]
Eligible percentage of cash equal to milestone payment				70.00%
Fair value of the intangible assets acquired				£ 14,500,000
Acquisition of cash and cash equivalents and short-term investments | $		$ 50.8
NAVI milestones [member] | Top of range [member]
Disclosure of non-adjusting events after reporting period [line items]
Maximum cash payment limit | $		$ 79.7
OncoMed Pharmaceuticals, Inc.[member]
Disclosure of non-adjusting events after reporting period [line items]
Issue of additional warrants to lenders | shares	321,444
Ordinary shares exercise price	£ 2.95
Voting equity interest rate	100.00%
Initial consideration purchase amount	£ 40,892,478
Initial consideration purchase, shares | shares	24,783,320
OncoMed Pharmaceuticals, Inc.[member] | TIGIT milestone [member] | Top of range [member]
Disclosure of non-adjusting events after reporting period [line items]
Maximum limit of enlarged Group after issuing the consideration shares			40.00%
OncoMed Pharmaceuticals, Inc.[member] | Unlikely scenario event [member] | TIGIT milestone [member]
Disclosure of non-adjusting events after reporting period [line items]
Initial cash milestone payment due			£ 35,000,000