v3.26.1
Document and Entity Information - shares
 3 Months Ended
Mar. 31, 2026
May 11, 2026
Document Information [Line Items]    
Document Type 10-Q  
Document Quarterly Report true  
Document Transition Report false  
Document Period End Date Mar. 31, 2026  
Document Fiscal Year Focus 2026  
Entity File Number 001-38452  
Entity Registrant Name MEREO BIOPHARMA GROUP PLC  
Entity Incorporation, State or Country Code X0  
Entity Address, Address Line One One Cavendish Place  
Entity Address, Address Line Two 4th Floor  
Entity Address, City or Town London  
Entity Address, Country GB  
Entity Address, Postal Zip Code W1G 0QF  
City Area Code +44  
Local Phone Number 333-023-7300  
Entity Tax Identification Number 00-0000000  
Title of 12(g) Security None  
Entity Shell Company false  
Entity Current Reporting Status Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business true  
Entity Emerging Growth Company false  
Entity Common Stock, Shares Outstanding   798,093,044
Entity Interactive Data Current Yes  
Entity Central Index Key 0001719714  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q1  
Ordinary Shares    
Document Information [Line Items]    
Title of 12(b) Security Ordinary Shares, nominal value of £0.003 per share  
Security Exchange Name NASDAQ  
American Depositary Shares    
Document Information [Line Items]    
Title of 12(b) Security American Depositary Shares, each representing five ordinary shares, nominal value of £0.003 per share  
Trading Symbol MREO  
Security Exchange Name NASDAQ