The film, which explores the life of Bradford playwright Andrea Dunbar, scooped the 'Best British Newcomer' and 'Sutherland' gongs at the awards ceremony last night.
The 'Best Film' prize went to Alexei Popogrebsky's Russian drama How I Ended This Summer, about two men stationed at a remote meteorological outpost in the Arctic Circle.
Actress Patricia Clarkson, who chaired the international jury, said of How I Ended This Summer: "Director Alexei Popogrebsky has combined stunning cinematography with painterly attention to production detail and drawn intense and subtle performances from actors Grigory Dobrygin and Sergei Puskepalis.
"The film turns the hunter-versus-hunted narrative on its head to provoke powerful questions about life and death, resilience and human compassion. Tense, moving and universal in its scope, this is a cinematic tour de force."
The 'Grierson Award for Best Documentary' was awarded to Janus Metz's Armadillo, an account of Danish soldiers in their first posting in Afghanistan.
"With total access and great honesty, the film shows us why these men want to go to war and what the experience of action does to them," said chair of the jury Kevin Macdonald. "Humane but clear eyed in its attitude to the conflict, we believe that Armadillo is a touchstone film that will be watched for years to come."
Danny Boyle, whose film 127 Hours will close the London Film Festival tonight, received the 'BFI Fellowship' from Stephen Daldry.