Film about British nonconformist (5)
I believe the answer is:
rebel
'nonconformist' is the definition.
(I know that rebel is a type of nonconformist)
'film about british' is the wordplay.
'film' becomes 'reel' (reel is a kind of film).
'about' is an insertion indicator.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'reel' placed around 'b' is 'REBEL'.
(Other definitions for rebel that I've seen before include "Revolting person" , "One who rises up" , "revolutionary" , "(One who) revolt(s)" , "Bolshy" .)