Essex Boys.
Rise Of The Foot Soldier
The Krays
The Business
Gangster No1
The Take(Martina Coles Sky 1 series, stars Tom Hardy)
Sexy Beast
Layer Cake
Top Boy(Channel 4 tv series on Hackney drug dealers)

EDIT: Whoops noticed you mentioned good films, some of these are questionable but worth a watch i guess. The Take is one of my favorites.