Not much to look at, the fool, and he's not in uniform (5,7)
I believe the answer is:
plain clothes
But I can't explain it at all! Could you help me understand?
(Other definitions for plain clothes that I've seen before include "Policeman's non-uniform wear" , "sort of detective" , "Act of bringing together (sides in dispute)" , "Mufti" , "uniform? Wrong" .)