Perhaps we’re still not sure what to make of Kevin Spacey here in the UK. A two-time Oscar-winning A-list actor settles in south London to battle against hostile critics and rebuild a tottering theatre. How would we have responded if Jack Lemmon had taken over the Old Vic? Or Meryl Streep? Probably the same - bitched and moaned, but secretly prayed they’d stay. “See?” we’d wonder to ourselves. “We’re still the home of proper theatre. But, really... Aladdin at Christmas?”

Curiously, our British sniping doesn’t seem to bother Spacey. Least of all today. I’ve interviewed him before, and the first thing I notice is that he looks… well ... relaxed. One might almost say happy. He asks polite questions about my own life – things he’s remembered that no stars ever do. Yet there is still something that seems ... coiled.

He is demonstrating his spring-load mechanism in two roles at the moment. In his new film, 21, he plays a professor who encourages a group of students at Massachusetts Institute of Technology to master card-counting and fleece Vegas. On stage at the Old Vic, he is cast as Charlie, the Hollywood hustler, opposite Jeff Goldblum in David Mamet’s Speed-the-Plow.

In 21, Spacey’s Professor Mickey Rosa tempts Jim Sturgess’s broke Ben Campbell into the darkness with Mephistophelean glee, then rabbit-punches him with such swift brutality, you’re left almost breathless. This is the beauty of Spacey on film - the nuance, the pause, the grin that charms and chills in equal measure. In Plow, the currents don’t run deep. Both characters explode - but, with Charlie, it’s constant combustion. “I guess they’re both desperate,” Spacey nods carefully. “Charlie’s never had anything of his own, and you get bitter about that. With Mickey - what does an MIT professor make? He realises he’s got these kids who are smart, but he can’t bankroll them; someone’s bankrolling him. So, when these kids get arrogant and stupid, he’s going to have to front that. He’s near the breaking point.” This used to describe Spacey himself. His early career was driven by manic intensity. Some nights, it got so bad he couldn’t sleep. He wanted fame so much, he’d do stand-up comedy at midnight in bowling alleys. Then, in 1986, he fought like fury to play Jamie in a Jonathan Miller-directed version of Long Day’s Journey into Night. Jack Lemmon played his father - a crucial moment for Spacey, as it was Lemmon’s kind words, during a youth workshop in California, that had set him on his way.

“I had no self-esteem when I was a kid, I was so shy,” he recalls. “But when you’re 11 years old and have Jack Lemmon say you’re good ... It changedmy life, it gave me confidence.”

Touring Long Day with Lemmon, he found something more - a mentor to replace his hapless father. “Not all actors are the same, but I think there is a nomadic quality to the life.” He steps cautiously. “And the way that I was raised … Well, my family moved a lot, because my father was unemployed a lot and lost jobs regularly, so we couldn’t pay the rent. In some cases, we moved houses within blocks of each other. I think there was something about that sense of being uprooted ... Well, I was young and inexperienced, and I remember being very angry with my father.”

I wonder if the anger died with his father or drove him on - so many of his parts have a desperate rage uncoiling within. “My dad and I ... There were things we hadn’t discussed until the last year of his life, and we had a grand number of conversations in which we ... He understood my point of view, and I understood his point of view and forgave him. I realised I couldn’t have done any better in his shoes, given his circumstances. I realised how much that kind word from Jack changed my life.”

What would have happened if Lemmon hadn’t spoken? Spacey shrugs. “I don’t know, because there was that nine, 10-year period when I was a bit rambunctious. I didn’t know what I wanted to be, and my dad was like, ‘You’re going to military school’ – and that didn’t work ...”

Articles about Spacey often trot out a story that the actor was going off the rails, on the verge of juvenile delinquency, at this stage. I ask if this is true. Then Spacey - Hollywood superstar, double Oscar-winner, friend of presidents - leans back in his chair and slowly, deliberately makes a crude male gesture of a kind you might expect from a white-van man you have overtaken badly, but not from a former presenter of the Nobel Peace Prize. While all the time shaking his head, wearing a geezerly grin. Living in south London is clearly having an effect. “You mention two things you did when you were a kid that any kid does and suddenly you’re this rebel without a cause,” he sighs. “Too much has been made out of that. Like recently, I said - as I’ve been saying for four years - that my priorities have changed and I’m more focused on the theatre in London. Then I read articles saying I’m retiring from the film industry. Suddenly my friends think I’m shitting on them. Sometimes I think, ‘Perhaps I should never say anything, because I’m no longer talking to you, I’m talking to the internet.’”

If those are sensitivities, I plead, why choose London, where we have a tabloid-newspaper industry that invented that sort of thing? “I always get this very odd ‘Why did you walk away?’ question,” Spacey says, laughing. “I didn’t walk away, I walked towards. I got to a place where I said, after 12 years living in hotels as a nomad, ‘How can I have a better life?’

“I have a revulsion for the word celebrity. I’m a relatively ugly character actor who’s done pretty damn well in film. So I thought I’d like to spend 10 years doing something that I know will change the quality of my life. And the most important part of that is mentoring young talent – at last year’s Edinburgh Festival, 54 plays began life with the Old Vic New Voices programme.” He beams uncontrollably.

Why does that make him smile so much? He shoots back: “Because it makes me feel like I’m doing what I should be doing.”

Why? “Because I had some really f***ing great mentors in my life, who passed down what in my estimation were some pretty wise ideas. Especially after my father died, Jack Lemmon became a father figure to me. Jack always used to say that if you’ve done well in the business that you wanted to be in, then it is your obligation to send the elevator back down. That’s your job, because somebody did it for you. It’s more satisfying than any individual achievement because you can change people’s lives.”

What about the press? “I think that’s over now. If you look at the first three years of the RSC, the first three years of Peter Hall at the National, or Richard Eyre, or Sam Wanamaker and the Globe, you think, ‘Oh, this is how theatrical beginnings are welcomed.’ There’s a trial by fire. Add to that an American movie actor, and you can understand why we went through it. But by the middle of our fourth season, more than 950,000 people have come through our door, 37,000 kids have taken advantage of our cheap seats – thousands of kids in workshops and thousands of locals who’ve never been in the Old Vic before.” So you’re happy, I say. “I’m happier now than I’ve ever been.” And here to stay? “I’m now thinking in terms of the work I want to do in this theatre over the next seven or eight years,” he says. “I want to challenge myself with some of the great parts.”

Oh, I say, what great parts? He laughs: “No chance, son!” South London again! “If I told you what my top five were, I’d be reading for the next year and a half what they were, why I haven’t done them, and that I’ve changed my mind or something fell apart.”

Then he guides me to the door like a cocky Lambeth publican at last orders, promising to “sort me out” with a couple of tickets for Speed-the-Plow.

It may be we’re not sure what to make of Spacey as a Hollywood ace face. Perhaps it will matter less as his south Londoner metamorphosis continues. Just watch out if he starts wearing a car coat.

21 is released on April 11; Speed-the-Plow is at the Old Vic, SE1, until April 26

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