Spot the English agent (4)
I believe the answer is:
espy
'spot' is the definition.
(I know that spot can be written as espy)
'english agent' is the wordplay.
'english' becomes 'E' (abbreviation).
'agent' becomes 'spy' (spy is a kind of agent).
'e'+'spy'='ESPY'
'the' acts as a link.
(Other definitions for espy that I've seen before include "Behold" , "Watch" , "Observe, notice" , "Perceive" , "Detect" .)