Information gathering on politician (5)
I believe the answer is:
green
'politician' is the definition.
(eg member of the Green Party)
'information gathering on' is the wordplay.
'information' becomes 'gen' (gen can informally mean information).
'gathering' is an insertion indicator (gather can mean to acquire or bring in).
'on' becomes 're' ('on' can be mean 'with reference to').
'gen' enclosing 're' is 'GREEN'.
(Other definitions for green that I've seen before include "Consultative document" , "Gullible" , "Caring for environment" , "personification of envy" , "Like lettuce" .)