Fiend’s name covered up by British gang member (7)
I believe the answer is:
mobster
'gang member' is the definition.
(I know that mobster is a type of gang member)
I can't explain the remainder of the clue.
(Other definitions for mobster that I've seen before include "family man" , "Hoodlum" , "Mafioso" , "Organised criminal" , "Gangster" .)