'Truly great parts come along so rarely'

Jason Isaacs tells Neil McCormick why he chose to play a man of extreme violence

Jason Isaacs has established himself as one of Britain's leading actors. He's receiving the star treatment for his role as our man in Washington, Sir Mark Brydon, in the BBC series The State Within, and is a veteran of more than 30 movies, including the Harry Potter series.

	Battle scars: Jason Isaacs plays Chris

But tomorrow night, on Channel 4, he turns up in a very different context in the gritty docu-drama Scars, as a working-class family man struggling to come to terms with his criminal past of horrific hooliganism, armed robbery, torture and, possibly, murder.

There is no action, no special effects and virtually no other actors, just Isaacs holding centre stage in an unfolding dialogue with writer-director Leo Regan, shot on a hand-held digital video camera in long, continuous takes, delivering one of the most compelling portraits of barely repressed violence since Robert De Niro in Taxi Driver.

"At this stage in my so-called career, I shouldn't be doing something like this," says Isaacs. "I made the stupid mistake of opening the script at four o'clock one morning, jet-lagged from a six-month shoot in America, and I sat there absolutely electrified. Truly great parts come along rarely in an actor's life, if ever. You're lucky if you get one, and I had a feeling this might be it."

Bafta and Director's Guild award-winning filmmaker Regan admits to having been sceptical about working with Isaacs. With a background in documentary, Regan initially contemplated using a non-actor, perhaps a reformed criminal, thinking that might give the performance more authenticity.

But, at the behest of his production company, he went to a meeting with Isaacs. "There was something about his eyes, his presence; my instant reaction was: 'He's the right guy,' " says Regan. "But as soon as he spoke, that all evaporated.

"He's a lovely, charming man and the story I wanted to tell was about an ugly, horrific, damaging way of life, extremely destructive to a lot of people, including the individual himself. Watching films, the messages about violence tend to be glamorous and seductive, but I wanted to make something that showed there's nothing romantic about it, that it's disgusting."

The preparation process was fraught, with Regan pushing Isaacs to his creative limits. "It needed to be beyond a performance, it had to come from somewhere real, and I had to feel that." He persevered because producer Jane Featherstone assured him that Isaacs "was a special actor and he had it within him to be fantastic. She was right, but it took a lot – on both sides – to get there."

The real-life inspiration for Chris, the central character, is someone Regan had met while researching another project. "He had no desire to tell his story, but once he started he couldn't stop," says Regan. "It was like a compulsion."

Revealing the extent of his violence to another person for the first time led "Chris" close to psychological disintegration. "We went on an emotional journey together and the process wasn't necessarily good for him, in the short term at least, but I think he needed an outlet, because it was killing him."

Regan's script dramatises the interview process itself, with word-for-word recreations, because "some things you can't access with a documentary camera. He wouldn't be filmed; he wouldn't incriminate himself. What is important to me is the story, and I use whatever tools I can to tell it."

Scars was originally commissioned for the Freeview channel More4, but critical acclaim has led to its first terrestrial broadcast tomorrow. Isaacs was involved in shaping the final script.

"It became an engrossing mission, not to forgive or paper over the cracks of someone who is clearly very dangerous, but not to repel the audience so that they couldn't feel they had access to him. Leo's gift is to peel back the layers and expose his essential humanity, and that is a humanising process for all of us."

"I think Chris is very damaged, and I'm appalled by the things he's done, but I do feel for him," says Regan. "To walk away from that life of violence was courageous. To take this project on and open up to someone was also very courageous. Because that is just something he doesn't do, that no one from his world does – they don't talk."

Isaacs says: "It's very scary to know that such extreme, life-changing violence bubbles along as a kind of undercurrent, a tide, all around us on the pavements and the roads. People laugh at the whole method thing, but the truth is that acting is an incredibly simple thing to do that's very difficult to achieve: you just have to believe you are that person in that situation.

"And this guy is in a terrible place, deeply miserable and filled with rage, often stoned and drunk because it's the only way he can cope with the stuff that swirls around his head. And there was no break from it. It was all me, every day, all day.

"I kind of lived with him in my head more than I've ever done before. But an actor can only ever be as good as his material, and you don't get much richer material than a real, complicated human being in terrible pain."