"We have great fun, we have this outrageous Cork humour we can draw on," he says, smiling. "In a mother and son relationship, it's nice to have that connection. It's irrelevant, and you're not going to see it on stage, but it's nice for us to have it."

The cast have had plenty of time for bonding; three weeks rehearsing at Stein's mansion in Italy—"the most picturesque cigarette breaks in the history of theatre"—and three days in Russia, where they met their opposite numbers in the Russian version of the play which Stein is planning. "All very serious and passionate people, we were going around smiling at them till our faces hurt."

Murphy describes himself as "a complete Chekhov virgin" who jumped at the chance to work with Stein. At 27, an exact contemporary of Colin Farrell, who is a friend, he has appeared in several acclaimed independent films, most notably playing the lead in Danny Boyle's low-budget zombie movie 28 Days Later... His latest film, Intermission, which also stars Farrell, has its U.K. premiere at the Edinburgh Film Festival. Other forthcoming movies include Girl With a Pearl Earring, with Scarlett Johansson and Colin Firth, and a small part in Anthony Minghella's Cold Mountain.

Slightly built and casually dressed, he wouldn’t stand out in a crowd if you didn't meet his eyes—intense deep-water blue and used to great effect in 28 Days Later... "Slow-burning charisma" is a phrase that gets used. He talks about himself as an accidental actor. "I very quickly forget that I'm an actor when I'm not doing it, I guess because I never studied it, I never had a burning passion. I just acquired that later on."

Murphy dropped out of a law degree to take a part in Enda Walsh's Disco Pigs, a hit at the Fringe in 1997. Pat Kiernan, the director of Corcadora Theatre Company in Cork, remembered him from a schools workshops (sic) and asked him to audition. "It's a complete cliche, but there's truth in cliches, right? It [Disco Pigs] did change the course of my life.

"I was going to be back in college for October. But the play did very well, and I very quickly fell in love with the whole theatre life and the people I met. I was never very enamoured with law either as a course or as a life."

He says he's been lucky. Blessed with surprise hits. Like 28 Days Later..., in which he plays a courier who wakes from a coma to find London a ghost town populated by zombies with a rage against humanity. "The only thing that I do insist on is diversity, and doing a post-apocalyptic zombie movie, having just come off a adaptation of a Trollope [The Way We Live Now] was exciting and weird. The weirdness of it appealed to me.

"In hindsight, you can see that it was clever. There hadn't been a movie of that genre for a long, long time and they’d updated it and modernised it. But I was completely unprepared for the success of it in America. I thought the Americans would not be able to take something like this at this point. But obviously they’re smarter than we think," he pauses, for a brief thought. "It's only their president that's a monkey."

He says the film's success lies in the fact that it works both as a simple horror film and a more sophisticated piece of analysis. "I was never aware during it that we were making a zombie movie, I thought it was a film that was commentating on the state the world is in, the symptoms of global paranoia, air rage, road rage, phone rage, that sort of thing. I was more intrigued by that than by running after monsters, although that was fun too! Shooting guns and fighting is always good for boys to do."

It could bring him to the attention of the major players. Does he fancy following Farrell to Hollywood? "I couldn't live in L.A., but I would love to be involved in American films. A lot of my favourite directors are American. But when people talk about Hollywood, the image it conjures up is riding around in limousines and going out with anonymous blondes. That doesn't appeal to me."

Every script that comes through the door, he says, will be judged on its own merits, which is one reason for choosing to do Intermission, a low-budget ensemble movie set in Dublin, written by playwright Mark O'Rowe and directed by John Crowley (who, he points out, happens to come from Cork). Colin Farrell gave his name to the film at an early stage. Colm Meaney, Kelly McDonald (sic), and Shirley Henderson also star.

It's a movie about ordinary lives and extraordinary people whose fates interweave, taking in a bus crash, a bungled bank robbery, and a broken love affair. "It was one of the best scripts I have read in a long time. I hope it is liked because I believe in it a lot."

So, I ask him, if it wasn't for Disco Pigs, would he be a Dublin lawyer by now? "I'm bad with hypothetical questions, but I could say emphatically that I would not be a lawyer," he grins. "I failed first year anyway!"