Politician without a plan (3)
I believe the answer is:
map
'plan' is the definition.
(I know that map is a type of plan)
'politician without a' is the wordplay.
'politician' becomes 'mp' (Member of Parliament).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'mp' placed around 'a' is 'MAP'.
(Other definitions for map that I've seen before include "face" , "Travel guide" , "Chart" , "Geographical plan" , "Representation of earth's surface as a guide" .)