Financial instruments fair value disclosures- Summary of Changes In Significant Unobservable Inputs Under Valuation Model Used In Level Fair Value Measurement (Detail) - GBP (£)	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021
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]
WACC	14.00%	12.00%
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	£ 45,000	£ 31,000
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	£ 500,000	£ 500,000
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	40.60%	40.60%
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	81.20%	81.20%
Weighted average [member] \| Expected Volatility Member [Member] \| Warrants Related To Pipe member [Member] \| Black And Scholes Method [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Expected Volatility	116.30%	75.10%
Weighted average [member] \| Expected Volatility One [Member] \| Warrants Related To Pipe member [Member] \| Black And Scholes Method [member]
Disclosure of significant unobservable inputs used in fair value measurement [line items]
Expected Volatility	149.00%	67.40%
Financial liabilities, at fair value	£ 10,200,000	£ 6,700,000

The fair value of financial liabilities. [Refer: At fair value [member]; Financial liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2021-01-01
-Paragraph 25
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2021-en-r&anchor=para_25&doctype=Standard
-URIDate 2021-03-24

+ Details

Name:	ifrs-full_FinancialLiabilitiesAtFairValue
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The percentage of a reasonably possible increase in an unobservable input used in fair value measurement of assets.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 13
-IssueDate 2021-01-01
-Paragraph 93
-Subparagraph h
-Clause ii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2021-en-r&anchor=para_93_h_ii&doctype=Standard
-URIDate 2021-03-24

+ Details

Name:	ifrs-full_PercentageOfReasonablyPossibleIncreaseInUnobservableInputAssets
Namespace Prefix:	ifrs-full_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Clone 1 Of Disclosure of significant unobservable inputs used in fair value measurement [line items]

+ References

No definition available.

+ Details

Name:	mreo_DisclosureOfSignificantUnobservableInputsUsedInFairValueMeasurementLineItems
Namespace Prefix:	mreo_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Expected Volatility Percentage.

+ References

No definition available.

+ Details

Name:	mreo_ExpectedVolatilityPercentage
Namespace Prefix:	mreo_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Increase Decrease in sensitivity analysis affecting input to fair value

+ References

No definition available.

+ Details

Name:	mreo_IncreaseDecreaseInSensitivityAnalysisAffectingInputToFairValue
Namespace Prefix:	mreo_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage Of Increase Decrease in sensitivity analysis affecting input to fair value.

+ References

No definition available.

+ Details

Name:	mreo_PercentageOfIncreaseDecreaseInSensitivityAnalysisAffectingInputToFairValue
Namespace Prefix:	mreo_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of weighted average probability.

+ References

No definition available.

+ Details

Name:	mreo_PercentageOfWeightedAverageProbability
Namespace Prefix:	mreo_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	mreo_SignificantUnobservableInputsAxis=mreo_WeightedAverageCostOfCapitalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mreo_CategoriesOfFinancialInstrumentsAxis=mreo_ProvisionForDeferredCashConsiderationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=mreo_DiscountedCashFlowModelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mreo_SignificantUnobservableInputsAxis=mreo_ProbabilityOfSuccessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mreo_SignificantUnobservableInputsAxis=mreo_ExpectedVolatilityMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mreo_CategoriesOfFinancialInstrumentsAxis=mreo_WarrantsRelatedToPipeMemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=mreo_BlackAndScholesMethodMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mreo_SignificantUnobservableInputsAxis=mreo_ExpectedVolatilityOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: