The award was presented on Wednesday night at a ceremony hosted by Marcus Brigstocke.
Jury chair John Madden described the film as “a sublime, uncompromising tale of the torment that can stand in the place of love.”
The best British newcomer award, presented in partnership with Swarovski, went to Junkhearts actress Candese Reid. The award includes a £5,000 bursary courtesy of Swarovski.
The Sutherland Award, presented to the director of the most original and imaginative feature debut in the Festival, went to Pablo Giorgelli for Las Acacias.
Werner Herzog’s Into the Abyss: A Tale of Death, A Tale of Life won the Grierson award for best documentary.
As previously announced, Ralph Fiennes and David Cronenberg were awarded the BFI Fellowship – the highest accolade that the British Film Institute bestows.
Greg Dyke, Chair, BFI said: ‘The BFI London Film Festival Awards pay tribute to outstanding film talent, so we are delighted and honoured that both Ralph Fiennes, one of the world’s finest and most respected actors and David Cronenberg, one of the most original and ground-breaking film directors of contemporary cinema, have both accepted BFI Fellowships – the highest accolade the BFI can bestow.
“I also want to congratulate all the filmmakers and industry professionals here tonight, not only on their nominations and awards, but also for their vision, skill, passion and creativity.’