In back lot, union leader bearing volatile solvent (7)
I believe the answer is:
toluene
'solvent' is the definition.
(toluene is a kind of solvent)
'in back lot union leader bearing volatile' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'lot' is 'tol' which is present in the answer.
'union' could be 'u' (common abbreviation as in 'Trades Union Congress') and 'u' is located in the answer.
'leader' could be 'e' (I've seen this in other clues) and 'e' is found within the answer.
'bearing' could be 'ne' and 'ne' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for toluene that I've seen before include "Hydrocarbon in petrol" , "flammable liquid" , "Constituent of petroleum" , "One lute (anag.); a solvent" , "Explosive material" .)