Possibly Rumpole's vehicle will turn up in garden (6)
I believe the answer is:
horace
'possibly rumpole's' is the definition.
(John Mortimer character Horace Rumpole)
'vehicle will turn up in garden' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'will turn up' says the letters should be written in reverse (in a down clue, letters go up).
'in' indicates putting letters inside.
'garden' becomes 'hoe' (to garden could mean to hoe).
'car' written backwards gives 'rac'.
'rac' placed into 'hoe' is 'HORACE'.
(Other definitions for horace that I've seen before include "Roman poet and satirist" , "Roman lyric poet, d.8BC -- a chore (anag)" , "- Walpole, eighteenth century English author" , "Odist" , "Is it a chore to read this old Roman poet?" .)