He’s left to take back six in the vehicle (7)
I believe the answer is:
marxist
'he's left to' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'back six in the vehicle' is the wordplay.
'back' says the letters should be written backwards.
'in the' is an insertion indicator.
'vehicle' becomes 'tram' (tram is a kind of vehicle).
'six' placed into 'tram' is 'tsixram'.
'tsixram' back-to-front is 'MARXIST'.
'take' acts as a link.
Can you help me to learn more?
(Other definitions for marxist that I've seen before include "Type of communist" , "left-winger" , "Red" , "left-wing" , "Revolutionary" .)