Trudge like a policeman (4)
I believe the answer is:
plod
This clue is a double definition.
'trudge' is the first definition.
(I know that trudge can be written as plod)
'policeman' is the second definition.
(UK informal term for a police officer)
'like a' acts as a link.
(Other definitions for plod that I've seen before include "Trudge wearily" , "Walk heavily (like a policeman?)" , "Walk slowly and heavily" , "Work doggedly" , "Work painstakingly" .)