Either it’s a bizarre accident, or there’s something in the water. Port Talbot, the unlovely steel town in Wales where smoke stacks belch fumes into the cloudy coastal sky, has been sending its sons to Hollywood for decades now. Richard Burton was the first to put his glowering blue eyes and golden larynx at the service of Tinseltown. Anthony Hopkins, for all his American passport, has never shed the native tinge from his accent. And now there is Michael Sheen.

In recent years the dynamic and febrile actor has been cornering the market in portrayals of figures who loom large in the national consciousness. He did a marvellous Kenneth Williams on TV in Fantabulosa!, uncannily capturing both the preening cockatoo and the miserable spinster. And we all saw his Blair. Stand by, in short order, for his Frost and his Clough. The two lead roles will give his home town further cause for the sort of civic pride that found one hotel summoning him home to have a room named after him.

“I sat there,” recalls Sheen in the sinewy Welsh accent that he has almost never used as an actor, “and listened to a male-voice choir sing We’ll Keep a Welcome in the Hillsides, which is very clichéd, but I still cried. It was a toss-up between the Michael Sheen banqueting suite and the Michael Sheen honeymoon suite, in which case there would have been a painting of me above the bridal bed. I said, ‘I think probably the banqueting suite. I don’t want to be looking down on people doing that.’”

This choice was kind of appropriate. Sheen is not the sort of actor who gets to do much of that on screen. He might have managed it in his private life, having a long-term relationship with Kate Beckinsale, which in 1999 produced a daughter. But right from the start it was clear that he was more suited to playing misfits than romantic leads. Reviewers went slack-jawed at his mercurial brilliance as a stage actor fresh out of drama college. As Peer Gynt, Mozart and Caligula, he scampered effervescently about the stage being not quite the full shilling. This was the type of talent that rarely prospers on the big screen, where quiet intensity is usually preferred. For years his knock-backs in Hollywood went along the lines of: “Sorry. We love what you do but we need a name.”

Although he’s never been out of work, the career only really took off when, in The Deal, Sheen was cast as the bright-eyed young Tony Blair. His chillingly likeable PM-in-waiting inaugurated a collaboration with the writer Peter Morgan which produced a second stab at Blair in The Queen. Now there’s talk of a third incarnation. He knew he had found a character worth sticking with while analysing the complex weave of real and faked emotion in Blair’s “people’s princess” speech. “There’s a moment in which he almost cries and you think, is that acting? People talk about the forced emotion of that speech. The problem is I think he was genuinely moved and at the same time aware that if he managed to pull it off it would be a big thing for him. When he talks about the two boys, I think he really is genuinely upset. But there are other bits where you go, that’s the worst acting I’ve ever seen.”

Since The Queen, Sheen has been preoccupied with another impersonation. Morgan’s play Frost/Nixon dramatised the gladiatorial encounter between the ambitious interviewer David Frost and the disgraced ex-president Richard Nixon. A hymn to the intrusive power of the goggle-box, it has made its way from the stage of the Donmar Warehouse to the West End to Broadway and now to the big screen. It’s a testimony to Sheen’s performance that the director Ron Howard insisted that Sheen be allowed to persevere as the smooth-tongued interrogator. Not that that’s the end of the writer-actor collaboration. Morgan has also adapted David Peace’s gripping, gruelling novel The Damned United, about Brian Clough’s star-crossed 44 days spent in charge of Leeds United in 1974.

“I was one of those people who would have said, ‘I can’t do impersonations,’” says Sheen. “I just wasn’t very good at it. Left that to other people. At the beginning of any of these projects, I start with the script, but I also watch the finished product on the screen in front of me and think: ‘I have to be that eventually.’ With Clough, for the first time I actually looked at photographs of him when he was younger and they could be pictures of me. But the worry was the same with all of them: that it’s not going to be believable.”

In each case Sheen has to transform away from the base metal of his own appearance and voice: a big-eyed, slim-faced man in his thirties with dark curly hair. He doesn’t look like a film star, but here he is, besuited in junket land with not one but two flak-jacketed adjutants from Los Angeles sitting in on our chat to make sure we all mind our p’s and q’s. I’ve been meeting Sheen for a while now. The last time, only a couple of years ago, he turned up on a motorbike in black leathers. It seems those days are over. Not that his elevation is unconditional. The Queen may have been a very successful film, but the pleasure Sheen took from it was tempered by the sight of Helen Mirren snaffling up every statuette on the planet, and her co-star winning pretty much zip.

“I would be lying if I said that it wasn’t in some ways difficult, because inevitably you act with someone in a film and you’re both playing the leads, and there was a huge discrepancy between the reaction to Helen and the reaction to me. That was already inbuilt in the film. It’s not called Blair. She’s such a gracious woman and it’s such a brilliant performance – that made it a lot easier to deal with. But nevertheless, I learnt a lot from going down that road. I learnt that the really important thing is to enjoy the process, and not to get too caught up in it all.”

Whether he learnt enough to protect himself from the same thing happening all over again remains to be seen. Sheen’s character gets to share the titular billing in Frost/Nixon, but you never know; it might happen all over again. Frank Langella as Nixon reluctantly scouring his conscience has more of the dark-night-of-the-soul stuff to sink his teeth into. He has already been nominated for a Golden Globe, while Sheen has missed out.

Sheen did not meet Frost until after he’d first said, “Hello, good evening and welcome,” on stage. The broadcaster came to an early preview, and Sheen knew something was up from the time it took the audience in the intimate theatre to settle. “He was quite shaken by the whole experience,” Sheen recalls, “but very supportive. You could see Frost the people person at work. Something about him was quite traumatised, and yet he was aware he was with people who have egos and insecurities, so he very generously was very positive, but he was also aware that this was something that was going to have a long life and it would be better for him to be on the side of it rather than against it.”

Sheen treasures a recent memory of his two worlds colliding when his parents visited Ron Howard’s set. “Ron likes people along, so you never quite knew who you were going to meet in the monitor room. One day, I went in and my mum and dad and David Frost were there with their legs dangling on all those director’s chairs, which are quite tall, all with those huge head-cans on, looking like Mickey Mouse. That was quite an image for me.”

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