Policeman and my last ape (4)
I believe the answer is:
copy
'ape' is the definition.
(I know that ape is a more specific form of the action mock)
'policeman and my last' is the wordplay.
'policeman' becomes 'cop' (slang term).
'and' says to put letters next to each other.
'last' suggests the final letters.
The last letter of 'my' is 'y'.
'cop'+'y'='COPY'
(Other definitions for copy that I've seen before include "written for paper" , "what's to be printed" , "Matter to be printed; ape" , "Reproduce" , "Replicate" .)