Ciaron Kelly has been acting since he was aged 10, going along every Saturday morning to classes at the Royal Scottish Academy of Music and Drama in Glasgow.

Kelly - a butcher's son who was born in Glasgow, grew up in Dalmuir, and now lives in Renfrewshire - took seven years to get his first professional job. He played a schoolboy who shoots his schoolmates and a teacher in an episode of Rebus. "It was one of the main roles, but I didn't have any lines," recalled Kelly, who is now 20.

And that was the only experience he had before applying to do a degree at the RSAMD and simultaneously putting himself forward for the new film Stone Of Destiny, with a cast that includes Charlie Cox, Robert Carlyle and Billy Boyd.

The good news was that he managed to get an audition for both. The bad news was they were on the same day and he was going to have to choose, with a fair chance that he might lose out on both.

He went for the long shot of a leading role as one of the four nationalist students (Ian Hamilton, Gavin Vernon, Kay Matheson and Alan Stuart) who secured worldwide headlines when they broke into Westminster Abbey and removed the Scottish coronation stone on Christmas Day 1950.

"I went in and did a really, really bad audition," said Kelly, who had little time to prepare for the part of quiet engineering student Alan Stuart.

Charles Martin Smith, the film's American director, who is better known as an actor in such films as American Graffiti and The Untouchables, turned him down, but suggested he try out for a minor role of a student in a pub scene.

"I thought I had made a big, big mistake," said Kelly. But he was not prepared to take no for an answer. "When I went back in for the recall I did my student scene first for Charles, and then after we had finished I said Charles, I have re-rehearsed the part of Alan, is it OK if I read that for you?' And he said Well, we've got about five minutes left, why don't you do that?'"

Kelly was recalled a few days later for a longer audition in front of the producers and got a phone call that night to say the part was his.

"I had only done Rebus before. Usually people do quite a lot of things and then do a movie, but I was lucky enough that Charles liked my re-audition and chose me."

Smith said: "He did a really good job. He's a really talented guy. There was a certain quality that I was really looking for in that character. I really wanted him to be the kid, as I believe Alan Stuart was."

One of the first things Kelly did was swot up on the Stone of Destiny. "When my agent phoned me up I honestly thought that it was a fantasy film," he said. As a Scot, he was ashamed to say that he had never heard of the coronation stone of the kings of Scotland, also known as the Stone of Scone.

The film is gently old-fashioned with elements of comedy. It had its world premiere at the Edinburgh Film Festival in June, where it got appalling reviews from local critics, though it scored highly on audience voting.

Kelly finally got to meet the real Alan Stuart in Edinburgh. "Nobody knew how to contact him At the premiere in Edinburgh, to our surprise, Alan Stuart was there, and it was such an honour to meet him. And the first thing he said to me was At least you've got hair.' He's living on the west coast of Scotland, he's retired and enjoying his life."

The film was subsequently chosen for the prestigious closing slot at the Toronto Film Festival, one of the most important in the world, and got a standing ovation. There are gala screenings lined up this week in Glasgow, Edinburgh and Oban, it goes on general release in Scotland on Friday and England in December.

Meanwhile, Kelly went on to appear in the series Lewis and is hoping his career will be further boosted when Stone Of Destiny goes on release. "It has always been my ambition to be an actor," he said.