Director Kevin MacDonald revealed he felt like a "fraud" when he collected his Bafta on Sunday for his docu-drama Touching the Void.
John Smithson produced and Kevin MacDonald directed Touching the Void
The film beat more traditional films such as Love Actually and Cold Mountain to land the British film of the year.
Despite his surprise at the win, MacDonald told BBC Radio 4's Today programme the viewers' response had been "amazing".
The film tells the true story of a disastrous climbing expedition.
Climbers Joe Simpson and Simon Yates attempted to be the first to reach the peak of the Siula Grande in Peru in 1985.
Although they reached the summit, on the way down Mr Simpson broke his leg and an effort to get the two of them back to base camp was defeated when he ventured over an overhang but could not get back up.
Mr Yates made the decision to cut the rope between them and leave his companion on the mountain in order to save one of them.
The film mixes true accounts with reconstructions
But against the odds Mr Simpson managed to get back down to base camp on his own.
Touching the Void is based on the book of Joe Simpson's survival and employs a mixture of real life accounts from the two climbers and reconstructed dramatic scenes on the mountain.
"We took the decision that the only way to tell the story was to use the real characters of Joe and Simon to tell their story to us directly to camera," MacDonald told Today.
"We were obviously quite nervous of making a foray into this territory."
He added that it was quite rare in Britain for people to go to the cinema to see a documentary-style film but viewers had felt "a strong emotion when they saw it".
"They can really relate to Simpson's predicament when he's in this awful situation and I think we have all been in terrible dark holes," he said.