French prison thriller A Prophet was hailed a "masterpiece" as it scooped the London Film Festival's inaugural best film prize.
Jacques Audiard's critically-acclaimed saga about a young man's rise through the criminal ranks was first unveiled at the Cannes Film Festival in May, where it took a prize for second place.
Anjelica Huston, one of the members of the London festival jury, called it "a perfect film ... an instant classic and a masterpiece".
The event, which is more than half a century old, introduced the award, similar to those handed out at other high-profile festivals such as those in Cannes and Venice, this year.
Speaking on the red carpet as she arrived at last night's ceremony, Huston joked that she was not necessarily the most sensible member of the jury.
Responding to whether she bossed the fellow members around, she laughed: "No not at all. They were incredibly compliant and sweet - no force needed with this group. They're a lot better than I am - much more grown up than I am!"
She added that, in her experience, water was the best ingredient to getting through an awards ceremony.
"A little champagne on the surface but water before you go out," she said. "It helps the next day!"
At the ceremony, the jury also gave a special mention to The Road, John Hillcoat's adaptation of Cormac McCarthy's post-apocalyptic novel.
Jack Thorne, screenwriter of The Scouting Book For Boys, won the award for best British newcomer, which was presented by Mamma Mia! star Dominic Cooper.
Cooper admitted that he was fortunate to break into the film industry relatively easily in comparison with most new stars.
"I made the transition through theatre really, so I was very lucky. But I imagine it's quite hard, it's difficult," he said.
Veteran British actor John Hurt and Malian director Souleymane Cisse received lifetime achievement awards known as the British Film Institute Fellowship.