JAMES McAVOY must be the world's most unlikely action hero. He has made his name playing raffish rogues (Shameless, Inside I'm Dancing, Penelope) and plummy-voiced young men (Becoming Jane, Atonement).

Yet here is a giant poster of new sci fi thriller Wanted with McAvoy looking rough and tough in a leather jacket, toting two guns and an expression that says: You lookin' for trouble, mate?

Except all of a sudden, the poster appears to be talking. It's standing outside the entrance to a room in London's Dorchester Hotel where McAvoy is conducting a whirlwind of interviews to promote Wanted. I've been busying myself trying to figure out if he looks harder than co-star Angelina Jolie on the poster (it's a draw) when the Scottish brogue comes to me. "You lookin' for me, mate?"

James McAvoy has stepped out of the room to wave another journalist off. "James," he says, warmly grasping my outstretched hand in both of his. We head into the room, where he waits for me to take my seat before he throws himself into the armchair opposite. Are action heroes meant to be this polite?

In the flesh, he's not one bit hard.

Lean, healthy-looking, with the striking blue eyes and handsome face of a romantic lead, yes. People magazine has voted him the world's fifth sexiest man alive -- just after Angie's partner, Brad Pitt.

But at 5ft 7in in his socks, this is not a man who you can imagine kicking seven different shades of anything out of Steven Seagal. Even Morgan Freeman, who plays his mentor Sloan in Wanted, seems to have a pop when McAvoy's character, weedy office worker Wesley Gibson, is presented to him for the first time. "I thought he would be taller," rumbles Freeman. Ouch.

But this is precisely the point, says McAvoy. "I do think that Wesley is an anti-hero, not a traditional action hero. He does bad things whether he thinks they are good or not; they are acts of revenge, but he still comes out as a hero."

Wesley Gibson is a 25-year-old bean-counting loser, whose girlfriend is cheating on him with his best friend. His boss is a bitch, his apartment is a hole and he suffers from debilitating panic attacks.

Then he meets uber-babe Angelina Jolie (codename Fox, natch) who snatches him from his humdrum existence. She and Freeman's Sloan recruit Wesley into the Fraternity, a band of merry weavers-cum-assassins, who take orders from the Loom of Fate -- bear with me -- to exterminate Very Bad Men and restore order to the world.

Wesley is told that his dad has been killed by a rogue ex-member of the Fraternity and he must avenge his death. So Wesley begins the transformation from office whipping boy to deadly assassin.

"I think I like the character of Wesley because he's one of these young people, in their 20s and 30s, where everything is fine and you can afford nice things. He's in a relationship that if he cared to, he could probably make right. But he can't understand why he's so unhappy," says McAvoy, pausing to mock himself for referring to 'young people' at the grand old age of 29.

Self-doubt is not a problem you could see McAvoy struggling with himself. He might not yet have hit 30, but he has already been described as one of the finest actors of his generation. He has worked solidly since he left drama college; acclaimed TV series like Band of Brothers, State of Play, White Teeth and Shameless were swiftly followed by the film roles.

He won a BAFTA for Best Supporting Role for Last King of Scotland and a Golden Globe nomination last year for Atonement.

"I've been very jammy," he says modestly.

Yet when he speaks of Wesley suffering from "post-modern angst and apathy", McAvoy knows what he's talking about. When he played the part of wheeler dealer car-stealer Steve in Shameless, he was on the brink of fame, but he has said in the past that it was also a point where he questioned if acting was really for him.

"I had a bit of a dark patch for a few months in Shameless," he admits. "We all get down from time to time, no matter how successful we are."

McAvoy, encouraged by Shameless co-star Anne-Marie Duff to believe in himself, decided to stick with his thespian instincts. He and Duff became a couple in 2003 and married in 2006.

The pair have been working in Germany together since April on a movie called The Last Station. They had been mooted to play parts opposite each other in an Irish film called Perrier's Bounty, but McAvoy says that while he had talks with the producers, it fell through. He cannot speak for his wife, he says.

The couple have a pact never to speak about each other in interviews. When I ask him about visiting Duff when she performed in the Druid Theatre's Playboy of The Western World, he prefers to talk about the "best fish and chips ever" that he had in McDonaghs of Galway.

But he laughs when I tell him a story about their appearance at the IFTAs a few years back. I had been chatting to a filmmaker friend of the couple when Duff and McAvoy wafted past, arms entwined. When I commented to the filmmaker that they looked very happy together, he replied that they were so happy, his last girlfriend had split up with him. "She turned to me and said, I think we should finish because every time I look at James and Anne-Marie I know we'll never be as perfect as they are together."

McAvoy tilts his head in amusement. "Oh my God, that's hysterical! We will bring doom your way! We will doom your relationship with our goodness," he jokes.

Having a fellow actor for a wife must make it easier to come home and explain you've spent the day kissing Angelina Jolie. In Wanted, he gets to lock lips with the most famous mouth in Hollywood -- although, he admits, it's a bit of a pity kiss for Wesley.

"It was just to piss off Wesley's ex, wasn't it?" he says. But what was it LIKE to kiss Angelina Jolie? "It's not half as nice as kissing someone you're actually in love with," he says. This could sound charming, or even cheesy, but from the serious-faced McAvoy, it sounds truthful. And, dare I say it, sweet.

"It's the hardest part of my job. I get totally atrophied and mixed up. You don't want to get too into it; you don't want to violate someone; and I don't want to be abused or violated either!"

One of his sexiest screen love scenes by far popped up -- ahem -- in Atonement, when McAvoy and Keira Knightley wrestle up against a bookcase.

"Joe [Wright, Atonement director] was great because he set the boundaries very clearly. When you have boundaries, you can totally go for it, you can get totally committed. Whereas if there are no boundaries, touching your hand to theirs might be too much, you know what I mean?"

While McAvoy might not ever be as statuesque as Schwarzenegger, there is still plenty of pocket-sized perfection for his female fans in Wanted.

"There was a lot of training," says McAvoy. "Six weeks before filming and then for the four-and-a-half months of the film, I'd spend an hour a day in the gym.

"The main stunt I did was f***ing dangerous. They wouldn't let me jump through a window, but they let me jump onto the hood of a car that was travelling 30 miles an hour along the road. There was no wires, no mats, nothing, that was just me. Then they slam the brakes on and I go flying off and a car slams into the side.

"I was asking, 'How can you let me do this if you won't let me jump through a sugar glass window that at the very most would scratch me?' Insurance people are funny."

Perhaps this chameleon-like quality is why James McAvoy is so successful. He wowed critics with his nuanced portrayal of a paraplegic in Irish film Inside I'm Dancing. Yet he can make his body do the talking in Wanted, hanging off a speeding train and taking knuckle-duster punches like a street fighter.

His swears like a sailor on Govan docks -- and yet politely rises to take me to the door at the end of the interview. He's the toast of Hollywood but prefers to live in a small flat in London, with a 10-year-old Nissan Micra for transport. He's a 29-year-old heart-throb who could have a world of women at his feet -- but he wants only the company of his lovely wife Anne-Marie, nine years his senior. All hail the anti-hero. n

- Susan Daly