NAME a Scottish musical that is not Brigadoon.

A tough one, right? Not for much longer. Sunshine On Leith, featuring songs from The Proclaimers, opens in cinemas next week. Surprise number one is that it is a big screen musical set in Scotland. Traditionally, Caledonia is to musicals what bricks are to swimming. Shockerooni number two is that it is directed by a Londoner, Dexter Fletcher (but written by a Scot, Stephen Greenhorn). Whammy number three comes courtesy of one of its stars, Paul Brannigan.

When asked by the filmmakers if he could sing, the Glaswegian confessed to attempts at Celtic Park or at karaoke, but he had a go.

"It turns out I'm not a bad chanter," says Brannigan, sounding amazed still.

But then it has been a surprising, bordering on surreal, few years for the 27-year-old. From appearing in Ken Loach's drama The Angels' Share, for which he won a Bafta Scotland Best Actor award, Brannigan landed the role in Sunshine On Leith, and is soon to be seen with Scarlett Johansson in the adaption of Michel Faber's science fiction novel, Under The Skin.

Between times he has played Gareth in the BBC soap River City. Little wonder that at the Edinburgh premiere for Sunshine On Leith, Fletcher predicted: "You're going to be seeing a lot of him."

Not bad for any young actor. But factor in Brannigan's beginnings, which include being brought up in Barrowfield with parents who were heroin addicts, running with a gang, serving three and a half years in Polmont Young Offenders' Institution for a firearms offence committed when he was a teenager, and his story starts to sound like a duff pitch for a far-fetched movie.

It is only too real, though, as he showed when he spoke about his life for a documentary made for the STV Appeal last year. Titled Born To Lose?, the film investigated the effects of poverty down the generations. Through winning parts in movies, Brannigan has had a chance to rewrite his script. While acknowledging his mistakes, he says his past is a part of his life. "That's all it is, a part of my life. Now this is a new part, a new chapter."

In Sunshine On Leith, Brannigan plays Ronnie, one of three Scottish soldiers (the others played by George MacKay and Kevin Guthrie) home from Afghanistan. Ronnie has suffered devastating physical injuries. As part of his research, Brannigan spoke to others in similar situations. "It opened my eyes to a lot of things," he says.

Too young to recall Fletcher from his Press Gang days, Brannigan knew him as the director of Wild Bill. "His energy is unbelievable. He keeps everybody going and he is full of laughs, but he is very clear in his direction and what he wants as well." While one might imagine Fletcher to have had a different directorial style to Loach, the two were surprisingly alike, says Brannigan.

"They are very similar in the way they speak to you and the way they treat you like a human being. Obviously Ken is older, he has not got as much energy as Dexter, but I have seen Ken running up and down hills in the middle of Inverness-shire with a pair of brogues on and nothing but a skinny jacket."

The weather was just as bracing on the shoot of Under The Skin, in which Brannigan shares an intimate scene with Johansson, who plays an alien landing in Glasgow. He admits to some nervousness in getting up close and personal with the Lost In Translation star. "At first I was a little shy and thought, 'How do I go about this?'" His instinct was to just be himself and it worked out fine.

Going with the flow, and grafting when given a chance, has worked well for him. Though slight - he makes Tom Cruise look like Arnie - he has the kind of presence that a stage school education cannot buy. It might have been different if not for that part in The Angels' Share. After Polmont he became a volunteer football coach, working with disadvantaged youngsters as part of a Strathclyde Police scheme. When Angels screenwriter Paul Laverty asked him to do the film, Brannigan hesitated. Laverty was not to be denied, though.

"At the time the funding had been cut for my post, I was a wee bit low on confidence and just didn't think it was right for me. Eventually, he got hold of me, gave me a kick up the backside and got me on board."

Television viewers will know Brannigan from River City, where he played Gareth, the one time bad lad desperate to go straight (in Angels he played a similar role). The soap has been his drama college, he says, not least in honing the discipline required for long days on set with script changes and pages of lines to learn.

Ask Brannigan if he identified with Gareth and he says: "I suppose in one sense I did. There is the falling in love, trying to turn your life around, but I tried to tap into something different." (Brannigan has a five-year-old son, Leo, with his partner Sheree.)

"He did what he did to survive," he says of Gareth. "Deep down he was a nice boy but just didn't know how to articulate that. Even in the show he doesn't know how to articulate it and sometimes it might come across as **** acting, but I hope it doesn't because he is meant to be awkward."

Brannigan still lives in Glasgow. I ask if he is in contact with his parents. "I'm still in touch with my dad, but haven't seen my mother for a while. As far as I know, she is doing okay."

Brannigan has been open about his past. The alternative, he felt, was that the story would have come out in bits here and there. He continues to give talks to youngsters about his experiences and still coaches football. He feels he has done his time, and it is time to move on. Not that this will prevent him being asked about his past in every interview he does, though.

He is ready for that. "They can take it whatever way they want to take it," he says of those likely inquiries to come. "I am happy with what I am doing in my life. I know my son will be proud of what I have done for him since he was born. Nobody can judge me because they have not seen what I have seen, and they have certainly not been through what I have been through. If they want to look down on me or judge me for that then they can go and take a flying you know what," he says.

Ask him about acting heroes and the names De Niro and Pacino come up, but they are followed swiftly by Peter Mullan ("a legend"), Ewan McGregor, Robert Carlyle and James McAvoy - all Scots, all working, as Brannigan will be, again, as he heads to London this week to start another film. In true movie industry fashion, he is sworn to secrecy about it. Brannigan knows where he has come from. Just as importantly, he has solid hopes about where he is going.

Sunshine On Leith opens in cinemas on October 4