Skin cracks, lips bleed, nails fall out - the camera rolls

When Kevin Macdonald won an Oscar for his documentary One Day in September, in 2000, such was the low cachet of the genre that instead of being lauded back home in the UK, his win was barely acknowledged. On both sides of the Atlantic, it seemed, everyone was fixated on fiction.

That erroneous state of affairs has since changed. Films such as Buena Vista Social Club, Bowling for Columbine and Spellbound have broken the confinement of documentaries to the small screen, proving that if a real-life story is engaging enough and told in a gripping way, the public will fork out for a cinema ticket. Macdonald's new film, Touching the Void - a tenser, more heart-in-mouth ride than any fictional drama you'll have seen this year - can only continue the trend.

One Day in September was a dazzling account of the assassination of the Israeli athletes at the 1972 Munich Games, told through newsreels, dramatic editing and a soundtrack that included Led Zeppelin. In terms of subject, content and style Touching the Void is a million miles away - or to be more accurate, several thousand feet.

Based on the book of the same name by Joe Simpson, the film charts Simpson's and Simon Yates' fateful attempt to scale the treacherous west face of Siula Grande, in the Peruvian Andes. Having successfully climbed the mountain, on their descent Simpson fell and shattered his leg. Yates's heroic attempts to bring his partner down the mountain with him, in dreadful weather, failed; after which the two men, oblivious of the other's fate, had to go it alone. That both did eventually make it to safety has become the stuff of mountaineering legend.

Their story was added extra vim by the fact that on their return from Peru, Yates was severely chastised by the mountaineering community for the taboo, apparently, of cutting the rope that joined him to his partner. The reason Simpson wrote his account of the experience was to defend his friend.

"I read the book in one sitting and just thought 'Wow what an incredible story, what incredible themes'," remembers Macdonald. But he wasn't convinced that he could make a documentary of it, until he sat Simpson and Yates in a studio and interviewed them for several hours in front of a camera. "For it to work as a documentary you have to see the people involved living the story. And I think you do with these two. I felt that both of them in their different ways were still very traumatised by the events."

The final film combines these "talking heads" with a very convincing dramatic reconstruction, during which actors (who had some climbing experience) play Simpson and Yates. "The thing about making documentaries is that you never know quite what you are going to get until you set off doing it," says Macdonald. "It's always a bit scary, always a challenge.

"With One Day in September, we were trying to come up with a new way of telling a current affairs story, and decided to do it like a thriller. I wanted to do this one as a full-on drama - for the actors to do as much of the climbing as possible, in as real a situation as possible, so that it doesn't feel phoney."

The crew filmed both at Siula Grande itself, mostly for landscape shots of the mountain in question, before shooting the climbing scenes in the comparatively safer environs of the Alps.

"Filming in Peru was very tough because our base camp was at 16,000ft and we went up to 18,500, which is really high if you haven't been that high before, and quite dangerous. You can get altitude sickness, in which case you're buggered basically, because you're four or five days walk from the nearest village."

"Altitude affects you in lots of horrible ways. You can't breathe, your skin starts to crack up, your lips bleed, your nails start to come out and you piss the whole time. And it's freezing at night. It's really unpleasant. I can't say how fantastic our crew were. The camera assistant literally collapsed of exhaustion."

Also with them in Peru were Simpson and Yates, who had gone along to appear in long shots in front of the mountain, because the actors had yet to be cast. "There was the weird situation of Joe and Simon playing the actors who were playing them," recalls Macdonald. "But they were very nervous about going anywhere near Siula Grande. They had an almost superstitious feeling about it."

Indeed, the climbers' reunion with the mountain did turn out to be misguided. "The return was really difficult for them. Joe and Simon both pretty much had nervous breakdowns out there. Joe and I had big bust-ups and he became quite difficult. When he came back to Britain he went to see a therapist who told him he was suffering from post-traumatic stress disorder, because he'd never dealt with it properly at the time."

Simpson and Macdonald are now back on good terms, with the climber actively championing the film. Yates, says the director, has basically washed his hands of it. "I think the whole incident is something he wants to put in the past, he doesn't want to keep having to go back to it anymore. Having to make a film about it was just one step too far."

Macdonald's interest in films blossomed when he wrote a book and made a documentary about his grandfather, the great writer and producer Emeric Pressburger, who with Michael Powell made such British classics as The Red Shoes and The Life and Death of Colonel Blimp.

While his brother Andrew has thrived as a producer of such crowd-pleasing features as Trainspotting and 28 Days Later, Kevin has focused on documentaries. At the same time, his filmmaking instincts and desire to reach an audience beyond television are not those of your average documentary-maker.

"Both One Day in September and Touching the Void - with the pacing, the scale of the visuals, the use of sound, the use of music - were planned as cinema events," he insists. "They're not TV films. It's hard to get people to see documentaries. If you say to people, here's a documentary about mountain climbers, they're gonna go 'Oh my God, I want to see Pirates of the Caribbean'. So for documentaries to work in cinema they have to be that much better than the feature film equivalent. They have to be bloody good, actually."

'Touching the Void' (15) is out on Friday