| Document and Entity Information | Jan. 08, 2024 |
| Document And Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 08, 2024 |
| Entity Registrant Name | MEREO BIOPHARMA GROUP PLC |
| Entity Incorporation State Country Code | X0 |
| Entity File Number | 001-38452 |
| Entity Tax Identification Number | 00-0000000 |
| Entity Address Address Line 1 | 4th Floor |
| Entity Address Address Line 2 | One Cavendish Place |
| Entity Address City Or Town | London |
| Entity Address Postal Zip Code | W1G 0QF |
| Entity Address Country | GB |
| Country Region | 44 |
| City Area Code | 333 |
| Local Phone Number | 023-7300 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001719714 |
| American Depositary Shares, each representing five Ordinary Shares, par value £0.003 per share [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | American Depositary Shares, each representing five Ordinary Shares, par value £0.003 per share |
| Trading Symbol | MREO |
| Security Exchange Name | NASDAQ |
| Ordinary Shares, nominal value £0.003 per share* [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Ordinary Shares, nominal value £0.003 per share |
| Security Exchange Name | NASDAQ |
| No Trading Symbol Flag | true |
