Steve McQueen’s Hunger: featuring one of cinema's greatest ever scenes

It is known simply as The Scene. To those who feted it at this year's Cannes Film Festival, and those who have seen it since, it is the breath-taking centrepiece of a film called Hunger that is both politically controversial and philosophically sublime.

It is 23 minutes of whiz-bang dialogue and crackling ideological debate between the movie's central protagonist, the IRA hunger striker Bobby Sands (Michael Fassbender), and a moderate Belfast priest, Father Moran (Liam Cunningham). The scene includes a 17-and-a-half-minute single shot of the two men – according to Guinness the previous record holder for a single shot on film (rather than video) is an eight-minute scene in The Player meaning that Hunger could be the holder of a new world record.

The scene in the film is set in the Maze prison meeting room, in 1981, just hours before the 66-day fast that would ultimately kill Sands, but it bristles with a modern intensity that speaks of a simple need for human understanding. Mostly, however, it is a masterclass in screen acting from two very different performers.

"I'm 31, and I left drama school here when I was 22, so I don't know why it's all happening now," says Fassbender, sliding into the sofa seat of a West London restaurant, shuffling up next to Cunningham. "Won't be long before you're under f***in' house arrest, like Brad Pitt," says Cunningham, gently needling him. They joke, too, about The Scene. About meeting each other for the first time in a Belfast pub with Steve McQueen, the director of Hunger, and how they bonded by nipping out for a smoke and, says Cunningham, "some heavy petting". "Yes," giggles Fassbender. "We called it The Passion."

Liam Cunningham: I remember Steve [McQueen] on that first day saying: 'I'm thinking of shooting this scene in one shot'. And my immediate reaction was, 'Are you out of your f***in' mind?!' So I ended up moving in with Michael.

Michael Fassbender: Into the spare bedroom of my waterfront flat in Belfast.

Liam: So every morning, we get up, he puts on the porridge and we start running the f***in' scene. At one there's a knock on the door and we're handed the food, and the door shuts again. We go on till six or seven o’clock until Steve turns up, looks at our progress, gives us some notes, and then off we go again. Running this scene 15 or 20 times a day for five days.

Michael: So when we arrived on set we just went straight into it [slaps his hand, clapper-board style]: Take one, 23 minutes, right through. We did four takes, and they used the fourth.

Liam: The irony is that now, with MTV editing, you're lucky to get a two-minute scene in total. Whereas here, we've got to hold people for the whole scene, and let them know that they haven't seen anything like this before.

Michael: We said it at the time: 'If this doesn't work, then we're'...

Liam: ... f***ed!

Hunger, though, is more than just a formal experiment. It's an interpretation of a real-life event during the Troubles in Northern Ireland, a period that is still to some, says Cunningham, "very much an open wound". Typically, for research, the actors met friends of Sands, and people who were "involved with the struggle".

"But I really don't know how much we want to get into that," Michael says sternly. He refused offers to meet the surviving Sands family ("I thought it would be a bit weird to get too close") and is aware of a media campaign to paint the film as a controversial canonisation of Sands, a convicted IRA gunrunner.

Michael: But it is controversial because it is our history. It is English and Irish history. And as soon as you put that on screen it becomes difficult.

Liam: The first thing Steve said to me was: 'We obviously are concerned about not making this guy out to be a hero!'

Michael: It's about human beings. It's about the prison orderly who sees Sands as a dying man, and tries to give him some dignity. Or it's the riot guard who's just a boy [Fassbender starts to well up], but who has to work up such hatred inside of himself in order to do his job. It's about what we're doing to each other as human beings. It's beyond politics.

On cue, and speaking of Hunger, the food arrives. Fassbender is having pasta, Cunningham lamb. They puncture the unexpected sobriety with discussion of Fassbender's shocking weight loss for the rest of the movie – the production shut down and the actor flew to LA and lived on berries and nuts for ten weeks, dropping more than 50lb.

"The nutritionist said that I shouldn't eat less than 900 calories a day," he says. "But the weight wasn't coming off, so for the last four weeks I went down to 600 a day" (a couple of cartons of blackberries and a sardine). He adds, though that on-screen emaciation can often be distracting for the public, and an obsession for the media. "It's like, 'You got down to 59 kilos? Oh really, we heard it was 56!' It shouldn't be about sensationalism. It should just be about maintaining the illusion."