Starring Sir Ben Kingsley and Jim Sturgess, Fifty Dead Men Walking is based on the memoir of the same name by Martin McGartland. The title refers to the number of lives allegedly saved by Mr McGartland’s actions from 1987 to 1991, says Steve Pratt.

FILMING a story about Irish Troubles in Belfast led to a tricky moment for star Ben Kingsley. “All I remember is in the hotel bar three very big chaps coming up behind me, shaking my hand, buying me a drink, shaking my hand again and walking away,” he says. “That was my heart-pounding moment with Belfast.”

In this real-life story, he plays Fergus, British handler of Martin McGartland, a 22-year-old from West Belfast, recruited by the British police to spy on the IRA in the Eighties. He was eventually discovered, but escaped and is still in hiding today.

It is reckoned that he saved as many as 50 lives as an informant – hence the title of the movie, Fifty Dead Men Walking.

The film also stars British actor Jim Sturgess as McGartland, Natalie Press and Kevin Zegers.

Scarborough-born Kingsley, an Oscar winner for his portrayal of Gandhi, was filming another movie, Elegy, when writer-director Kari Skogland approached him about the project.

“It was clear that she’d done a tremendous amount of research and was rightly sensitive to her mandate of keeping it balanced. She told me she had spoken to both sides of the conflict,” he recalls.

Kingsley sees a place in the cinema for a film about the Irish troubles and the people’s reaction during filming reflected this.

“There was a real urgency in Belfast for a perfect story of the troubles to be told and, in a sense, this is one of the perfect stories where you get a young man torn apart in the midst of this terrible sectarian violence,” he says.

He believes that the help the actors received from locals to master the accent illustrates the desire to collaborate and to perfect the story told by the film-makers.

“I hope – and I get the feeling it is – that the story is a genuine reflection of those really tough years. It’s specific. The more specific you get, paradoxically the wider the audience you’ll touch because only in the specifics of history do you get the bizarre events. If you generalise, it’s never as bizarre. This story is extraordinary, bizarre and at times absurd.”

He sees Fifty Dead Men Walking as specific as one of his previous acclaimed films, Schindler’s List, in that sense.

“When you examine under the microscope the journey of one man and the arc of that journey, it’s the stuff of great drama.”

While Sturgess and Zegers went to Belfast to research their roles and learn the accent, Kingsley was otherwise engaged making another movie. “I’m not playing a guy from Northern Ireland, so I felt it was perhaps excusable I didn’t go – I was more of an outsider in literal terms and performance terms.”

Sturgess lived and breathed the atmosphere in Belfast.

“The minute we got into Belfast and started speaking to the people this actually happened to, all these new stories would arise just chatting to the local people,” he says.

“Kari would come in all the time and say she’d heard this great story and had to put it in the film. It’s basis was Martin McGartland’s story, but then it really became the stories from the streets that we became part of while we were there.

“As a whole, we filmed around the same streets where it took place and we would revisit them time and time again.

“We got to know the people of the community really well, to the point where, if I had a quick costume change, we’d knock on their door, they’d invite us in, make me a cup of tea and a biscuit, and then send me back out to start filming again.

“When I was there, that was what blew me away about Belfast more than anything, it’s sense of community. They all look after each other. As a whole we were pretty well looked after by the people of Belfast.”

He was thrown in at the deep end with his West Belfast accent. Kari would order him out of the car in various areas of Belfast and tell him to try out his accent.

“It was sink or swim. We just integrated with the people as much as possible. That was my take on it.

I made a point, the minute I arrived, to hold on to it as much as possible,”

says Sturgess.

“Me and Kevin joined a local boxing club and stayed not so much in character but in voice. We got to be friends with people from the area.

“We’d go out to pubs, house parties and feel part of the city and become a part of the environment.

The more you do it, the easier and more believable it becomes.”

Kingsley remembers his first drive in the very difficult areas in which they filmed.

“My reaction was probably based on the characterisation I was trying to put together. I was looking through Fergus’s eyes a little bit. So in every doorway and in every window I saw a frown, I didn’t see welcome.

“In a sense that was feeding me.

I’m not saying the crew weren’t welcome, but there’s a curiosity in Belfast, naturally born of terrible violence and division, and I suppose in the car we were driving I was looked at with suspicion.”

Neither actor met the person on whom their character was based.

Sturgess says the approach is the same whether he’s real or fictional.

“You’re just trying to bring that character from the page, trying to bring him to life,” he says.

“I was fortunate I didn’t feel I had to copy or mimic him, be like him or use his mannerisms because, thankfully, for me he’s a hidden character, so no one knows exactly what he’s like.

“It wasn’t like playing an iconic figure where you have to get his characteristics down. It was liberating in that sense. It was more history of his situation rather than what he was like.”

Kingsley didn’t meet Fergus, although there were people associated with him around on set.

“I just built from one or two molecules,” he says. “There was a little bit of a tiny story that an actor told me whose brother was in the South Yorkshire police. I just built a little mosaic of a Lancashire police officer based on that.

“But they’re little catalysts really.

How we take the first step as actors is terrifying, but after you’ve taken that and the second step, you’re off.”

■ Fifty Dead Men Walking (15) opens in cinemas tomorrow.