Portion of film about British maverick (5)
I believe the answer is:
rebel
'maverick' is the definition.
(I know that maverick can be written as rebel)
'portion of film about british' is the wordplay.
'portion of film' becomes 'reel' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' is an insertion indicator.
'british' becomes 'b' (abbreviation e.g. in BBC).
'reel' enclosing 'b' is 'REBEL'.
Can you help me to learn more?
(Other definitions for rebel that I've seen before include "Refuse orders" , "Defy authority" , "Mutineer, one who defies authority" , "James Dean was one without a cause" , "Mutineer or dissenter" .)