Mr Meldrew is a winner (6)
I believe the answer is:
victor
'winner' is the definition.
(I know that winner can be written as victor)
'mr meldrew' is the wordplay.
'mr' becomes 'Vic' (short for Victor).
'meldrew' becomes 'tor' (I can't explain this - if you can you should believe this answer much more).
'vic'+'tor'='VICTOR'
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for victor that I've seen before include "Champion" , "The one who wins the battle" , "success" , "whiskey after this" , "One coming out on top" .)