Old Hillman's parking on back road (3)
I believe the answer is:
imp
'old hillman's' is the definition.
I can't tell whether this defines the answer.
'parking on back road' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'on' is a charade indicator (letters next to each other).
'back' says the letters should be written in reverse.
'road' becomes 'MI' (resembles M1 motorway).
'mi' back-to-front is 'im'.
'p' after 'im' is 'IMP'.
Can you help me to learn more?
(Other definitions for imp that I've seen before include "old graft" , "Little mischief-maker" , "Goblin" , "Small mischievous spirit" , "Mischievous child" .)