With his unruly mob of dark hair and lanky build, 27-year-old Andrew Garfield could easily be mistaken for tennis star Andy Murray, although his easy-going friendliness ought to be a quick giveaway. But never mind. All that is likely to change now that Marc Webb has chosen him to take over from Tobey Maguire in a 3-D reboot of Spider-Man, following eye-grabbing appearances in David Fincher's The Social Network as a Facebook geek who tries to do the right thing, and in Mark Romanek's hauntingly elegiac Never Let Me Go, where he's involved in a love triangle with Keira Knightley and Carey Mulligan.

"I've wanted to be Spidey since I was four," he says. "It's every skinny boy's dream."

Not that he really thought it was ever likely to come true when he was growing up in Surrey, where his father coached the Guildford City Swimming Club and also helped out with the British Olympic team. Spider-Man seemed too quintessentially an American comic icon.

"I've no idea why I was chosen, although I worked really hard for the auditions," he says. "I think it made a difference that my dad's American. He's from Los Angeles and my mum's from Essex. I've had the American accent in my ear all my life. I was brought up on American movies. I kind of have a sense of the culture maybe more than my English friends. I don't feel any more or less American or English."

He didn't see America again until 2007 when, just after winning the outstanding newcomer award at the Evening Standard Theatre Awards for his performance in Kes at Manchester's Royal Exchange, he successfully auditioned for Robert Redford's Lions for Lambs. "Stephen Daldry screen-tested me for a film he was doing and showed the tape to Redford's casting director Abby Kaufman. I heard I got the part [while] smoking in a cubicle at the Beverly Centre where I was buying a suit for the Golden Globes party. I went to Prince's after-party and threw up in his toilet."

Garfield was a gymnast and a swimmer at school, but quit sports when he was 13. "Acting came from me being depressed. I was a rather sad teenager. I didn't really know what life was about. I needed some kind of mechanism to figure it out. My parents suggested acting classes. I was in school plays and a teacher said I might be able to do it as a career. As soon as that happened I felt a sense of purpose."

Lions for Lambs is a political drama set in the course of a single day in Washington where an idealistic professor played by Redford tries to talk his star pupil Garfield out of political apathy. Simultaneously, an ambitious senator, Tom Cruise, is attempting to charm an investigative journalist, Meryl Streep, into running a story on a new military strategy in Afghanistan.

"I was scared at the idea of sharing the screen with such legendary actors. But as soon as I met Redford he put me out of my misery. He made me feel more at home than I've ever felt on a job. I don't think he enjoys that much the status that he has. He's just a people person. He comes from theatre, which reassured me because I do too. So we broke down our scenes into sections and objectives, but in a way that kept everything quite loose when we came to film, because he likes to improvise."

Lions for Lambs didn't turn Garfield's head. Rather than stay on in Hollywood he returned to England to play the title role in John Crowley's Boy A, which shared some similarities with the Jamie Bulger case. "I'm thrust out into society at 24 with a new identity after spending 14 years of my life in prison, without any experience of dealing with a job or with women or even with friends. It's sad but it's very beautiful."

To prepare for the role he visited detention centres with his co-star Peter Mullan, who had worked with young offenders. "Unlike Lions for Lambs, my character is terribly introverted and self-conscious. He is trying to find his way, kind of like me, except I was lucky someone got to me early and gave me confidence."

Between scenes on Lions for Lambs, Garfield would have discussions with Redford. "We'd talk about political issues to help keep us in the realism of the debate in the film. Like my character I found myself becoming more aware of things. My generation isn't apathetic, it's just that everything is so distorted by Fox News and politicians it's hard to access what's really going on."

So don't ask him about Afghanistan or the American mid-term elections.

"Right now I don't think it would be appropriate. I'm an actor. I read the Independent. I try to understand. But I don't feel educated enough to make statements. Maybe I will when I get to Redford's stage in life. He's a very gentle and encouraging man, as opposed to didactic."

'Never Let Me Go' opens on 11 February. 'The Social Network' is on release