Walk like a policeman (4)
I believe the answer is:
plod
This clue is a double definition.
'walk' is the first definition.
(plodding is a kind of walking)
'policeman' is the second definition.
(UK informal term for a police officer)
'like a' is the link.
(Other definitions for plod that I've seen before include "Stomp" , "Shamus, say" , "Walk along heavily" , "Walk laboriously, trudge" , "Slow heavy walk" .)