Pete Postlethwaite: The Pete who never met a dud

He has worked with Kevin Spacey, won an Oscar nomination, and even counts Steven Spielberg as a fan. So why, asks Toby O'Connor Morse, is Pete Postlethwaite embarking on a gruelling tour with a one-man show?

If you want to get an immediate impression of Pete Postlethwaite's varied career and the diversity of those who respect his work, just mention that you're meeting him for lunch. "He played that really cool lawyer in The Usual Suspects," says a thirtysomething friend. "He was brilliant in that thing where he worked in an undertakers," says my 77-year-old father, referring to the television drama The Sins. "He worked with Leonardo diCaprio on Romeo and Juliet," sighs my teenage niece. And my wife – not usually an autograph hunter – asks me to get a signature on her photograph of Postlethwaite in his stage role as Macbeth. He's on an awful lot of people's lists of top five actors – including Steven Spielberg's.

For a man who has such a powerful and riveting presence on the screen and stage, Postlethwaite in the flesh is a surprise: not quite shy or diffident, but quietly spoken, warm, convivial. Yet he is disconcertingly hard to read. Being an interviewer is in some ways like being blindfolded, trying to seek out the elements of the subject's personality with your fingertips.

This is tricky with Postlethwaite, since his off-stage persona has little topography, leaving the amateur character analyst to fumble around. Is he down-to-earth? Is he precious? When the character's mask is removed, the actor's face is strangely vague and hard to pin down. Only when he launches into an impromptu performance of extracts from his new play, Scaramouche Jones, does he spring into definition and become the man one thought one knew.

He is back in the rehearsal room at Bristol Old Theatre School where he studied more than 30 years ago. "Not in a million years would you think that the line of your career would go in the way that mine has. No way – we weren't even considering TV then. Theatre was what we were training to do."

The young Postlethwaite could not have foreseen the Oscar nomination (for his role as Guiseppe Conlon in In the Name of the Father), nor the fact that he would be playing Sophia Loren's husband in the forthcoming film Between Strangers. Nor his success in a host of television dramas. In fact, Postlethwaite has garnered acclaim across all the theatrical forms, and unlike many actors who have built their career in a single sphere, seems equally at home on the silver screen, the box, or the boards. He is the amphibious actor par excellence, slipping effortlessly between media.

"I think that's because I love good scripts, from Lost for Words [the television drama with Thora Hird] to Brassed Off. Even when I was eventually allowed to read the script for The Lost World: Jurassic Park, it was a ripping yarn. It was a good script, although I must say that it wasn't the one that eventually ended up on the screen."

This explains the weaving – and, to the outsider, sometimes inexplicable – path of his career: a love of the words, regardless of the medium in which he's going to deliver them. And a love of challenges. "They've all been script-driven really, with – I'm sure – an eye to 'what have I recently done, what would be radically different?' Because I think that has been a kind of game that I've played with myself, whether consciously or subconsciously: where's the next stretch?"

Postlethwaite's strength lies in suggesting the depths that underlie the character. Even as Roland Tembo in The Lost World, he gave the impression that his character had about 10 times as much back story as all the others put together. "One of the things that I want to do is make sure that the person is a complete person, and that no matter what kind of areas they go into, what kind of situations they have to face, somehow or other they're rooted, their feet are firmly on the ground, even if they are going to be taken off the ground for some reason or other." Postlethwaite gleefully quotes The New York Times review of Kobayashi, the deadpan lawyer he played in The Usual Suspects: "'This guy: he's got a false accent, he's got a false tan, he's got a false name, he wears false suits – and still we believe him' – that's what you want to hear."

Kobayashi, like many of Postlethwaite's characters, has a magnetic stillness about him. He seems to relish parts that offer the opportunity to do nothing, and to do it beautifully. This is no accident. He is dismissive of actors who desperately try to draw attention to themselves. It's not necessary. "If you've got somebody who is just thinking thoughts, the camera automatically wants to go and see what those thoughts are."

He stretched himself in a different direction when he took to the stage as Macbeth to widespread acclaim four years ago. It gave Postlethwaite a chance to apply his philosophy of finding the "person within" to a character who is often portrayed as pure evil. "Even with these extraordinary villains, more often than not Shakespeare will give you a little window that just goes right down, and you see the incredibly human soul of the man inside. Macbeth wasn't a villain: he was just swept along on this tide of ambition and it took him far beyond where he imagined he could go." Postlethwaite's Macbeth had the air of a lottery winner who couldn't believe his luck, and ended up writhing in agony as he was broken on fortune's wheel. "I don't know of many Macbeths with whom the audience have sympathised. Somehow or other people have got to be able to say, 'I recognise aspects of that character'. You could feel the audience going 'oh, poor bastard'."

And now he is back on stage again with a new play by Justin Butcher, Scaramouche Jones. It is a 90-minute one-man show, in which the eponymous 100-year-old clown recounts his life story on Millennium Eve. According to Postlethwaite, "It's a wonderful journey. He goes through the most extraordinary episodes in his life, but he always seems to bounce back. There is something tremendously endearing and enduring about somebody like that. And on a practical level, it's the distillation of theatre: storytelling. It's what all theatre is, all film, all TV."

He's taking the show on tour across the UK, including four nights at the 1,000-seater Belfast Grand Opera House. It will be a challenge, trying to fill a space such as that all on one's own, even for Postlethwaite. "My thought on that one is that if you take a photograph that's really sharp and focused, no matter how big you blow it up, it should still repeat, and still be all right. That's the theory."

He actually seems to be looking forward to finding out whether the theory works (and not apparently worried that it may not). But then, it is the thrill and challenge of the new that keeps him going, and keeps him fresh as he moves smoothly from Holly- wood trailer to shabby dressing room and back again. "What is the point of repeating something you know you can do? If it's not fraught with some kind of danger, I wouldn't really see the point." He pauses. "No – I wouldn't really see the point."

'Scaramouche Jones' at the Bristol Old Vic to 13 April (0117-987 7877), then on tour