THE moment it all struck home for Ben Barnes was when he was driving along Sunset Boulevard in Los Angeles and saw his face on a 60-foot wide billboard advertising Prince Caspian, the second instalment of CS Lewis's Narnia series.

A year earlier, the 26-year-old Londoner had been on stage in the West End, with just a handful of small movie credits to his name. Now he was the focal point of one of the year's biggest releases, tagged "Hollywood's Next Superstar" or "Hollywood's Biggest Heart-throb" almost universally in the press. "The first time I saw the billboard I was entirely breathless and speechless," says Barnes. "It made me feel very uncomfortable. Then, I drove past it a second time and I was like 'Yeah, baby'. I swerved into a gas station and got a disposable camera. I had to take about three shots just to fit me and the poster in." Although he has been acting and performing since his schooldays (he was briefly in a boyband which tried out for the 2004 Eurovision -- "not my proudest moment") his rise has been meteoric. He was approaching the end of a run playing Dakin in The History Boys at the National Theatre in London when he took a call from Andrew Adamson -- director of The Lion, The Witch and The Wardrobe (which grossed more than $750m at the box office) as well as Shrek and Shrek 2 -- asking him to audition for the title role in Prince Caspian.

A few weeks later, he was astride a horse in New Zealand on the set of the $400m fantasy epic. Caspian is a much darker, edgier and more enjoyable movie than the first instalment. Thankfully, he bears none of the hallmarks of a superstar or, worse still, someone who thinks they're a superstar. He is affable, funny and modest, but is acutely aware of what could lie ahead in an industry which never tires of putting people on pedestals.

"It's massive and it is very quick and it has taken me by surprise," he says of his rise. I point out that, while waiting for the interview, I inspected a whole range of action figures bearing his image. He's seen the toys and confesses a fondness for the sword, but admits "the whole thing is weird, and I feel very uncomfortable when people say things like 'movie star' and 'famous' because I just don't see it and I know that I'm never going to see that in myself.

"At the same time, I do get a bit irritated when people say, 'Oh it's like winning the lottery' and I'm like, 'No it isn't, because I've been working at this for 10 years.' I was aiming for it."

While he may have been aiming to make a big career for himself, the adulation, particularly from female fans is something that he is not yet used to, although it's fair to say that he welcomes it in some regards.

"If someone says to me, 'How does the whole heartthrob thing make you feel?' 'Vaguely embarrassed to be honest', is the actual answer. I just feel a bit silly when that's said to me. And of course, at the same time, 'amazing' because if girls think I'm a heart-throb then I stand a better chance with them. So both." He recalls arriving in Tokyo for the Japanese premiere and being greeted by 200 female fans watching his every move in silence. "They're so polite", he laughs. "Someone threw me a package and it was boxer shorts and I was thrilled, because I hadn't done any washing in days."

He's already realised that when fame comes along, suddenly everyone wants to be your friend. "I'm getting millions of texts from people saying 'I don't know if you remember me but...' I'm consistently impressed with how bold people are."

Born and raised in Wimbledon, his father is a psychiatrist and his mother a therapist -- a background which he says partly explains his success in his profession. "Between them, they were always asking me how I felt about things, so I'm sure that's got a bit to do with it, in so far as acting is about the hypothetical, of how you feel about things."

Music was his first calling (he still plays the drums) and while at college he sang in a band which performed at graduation. He was also signed to Simon Fuller, hence the boyband, which led to musical theatre. Several small television roles followed, as did a role in the Matthew Vaughn film, Stardust.

The scripts are now piling up, as are his credits. He's already appeared in a film adaptation of the Noel Coward play, Easy Virtue, in which he stars alongside Colin Firth, Kristin Scott Thomas and Jessica Biel who, he says, "is great in many ways". After he's finished promoting Prince Caspian, he'll take the title role in another adaptation, this time of Oscar Wilde's Picture of Dorian Gray. "I hope Ben goes on to do good work, rather than become a movie star," says Mark Johnson, producer of both Narnia movies. With a list of credits which includes Rain Man, Good Morning Vietnam and Donnie Brasco, Johnson knows what it takes to make a real actor. I put his comment to Barnes, who agrees with the sentiment that lies behind it.

"I'm not saying I'm not going to do a massive film with cars and guns, because if it looks really good and really exciting then why would you not? You've got to look at the careers of certain people. James McAvoy is a good example, having done the Narnia film and then made really interesting choices like The Last King of Scotland and Atonement, and now he's doing Wanted with guns and cars, and you believe him and he's a great actor and he's earned it.

"You can't ever copy anyone because the opportunities that are afforded to you will never be the same as theirs, but you can look at the people who are making good decisions and those who aren't. I just think you've got to do the films that you think are worth making."

The decision to accept the offer of Prince Caspian was obviously one that Barnes felt was worth making. He had six weeks left of his run in The History Boys but had to hand in his notice as he was needed on Narnia. The departure was acrimonious, with the producers, at one point, threatening to sue.

It is clearly something that still upsets Barnes, but he has no doubts that he made the right decision. "I still feel bad about it every day. I would have been a fool [to turn down Narnia]. There was no guarantee of anything after The History Boys. A few weeks later and I would have been unemployed."

Away from acting, he cites films, books and music as his indulgences. "I wish I had some crazy hobby like croquet or rock climbing but actually, I like spending my free time like other people's Sundays. You know, I go to the pub with my mates. I go and drink with my friends."

I put it to him that his new life must be something like the television series Entourage, in which the lead character Vinnie Chase moves from New York to LA with his childhood friends and begins making it as a Hollywood superstar. "I've seen every episode" he says. "When I was in LA, my life was just like the first season of Entourage." In the show, Vinnie Chase is swamped by impossibly beautiful women everywhere he goes. "The girl situation is not entirely like it is in the show," says Barnes. "Not just yet."

'The Chronicles of Narnia: Prince Caspian' is showing in cinemas nationwide

- Evan Fanning