If a star was born at this year’s edition of The Times BFI London Film Festival, it was Elizabeth Banks. Arriving at the premiere of Oliver Stone’s Bush biopic W., as her stunning Kaufman Franco dress shimmered in the glare of the flashbulbs, she worked the red carpet like a woman who knows her time has come.

After toiling away in everything from Shaft to Swept Away, maybe this is what ten years in the shadow of others does to you. Still, it is clear why Banks’s screen presence has been compared to Audrey Hepburn’s. While Steven Spielberg once told her, “I’ll never forget your laugh!” this was the night that Banks ensured we would never forget her smile.

The following day, sitting in her Knightsbridge hotel suite surrounded by the clutter of afternoon tea, Banks is a little stunned by all the attention. “It’s all a bit of a blur,” she admits, kicking off her shoes and curling her legs underneath her on the sofa. Still, she can afford herself a wry grin, well aware that the next fortnight’s film releases throw up what can only be described as a delicious juxtaposition.

Following her faithful First Lady in W. comes the new comedy from Kevin Smith, Zack and Miri Make a Porno, the story of two platonic friends who set out to make their fortune in amateur erotica.

Going immediately from the set of Smith’s film to W. in a matter of days, the irony was not lost on the 34 year-old actress (British audiences get to see W. in cinemas first). “I went from one bush movie to another Bush movie,” she grins. Notwithstanding the fact that, with her pert figure, blonde curls and bright-blue eyes, Banks is hardly a dead ringer for Laura Bush, was she shocked when she got the call from Stone? “I literally said to people, ‘Does he know that I just made a porno? Was he sure that he wants it to be me?’ Because I think that’s pretty hilarious and I think it’s going to cause controversy.”

The way that Banks bills it, Zack and Miri ... is a top-shelf title, though the truth is rather different. It is a love story at heart, as Seth Rogen’s Zack and Banks’s Miri unexpectedly fall for each other during the course of making their blue movie. After Rosario Dawson dropped out, Banks was recommended for the role by Rogen, with whom she starred in The 40-Year-Old Virgin. Claiming that she did no “additional research”, Banks found that her director and co-star had their uses. “I relied a lot on the encyclopaedic knowledge of pornography that Kevin and Seth brought to the film. They really knew a lot!”

While Banks calls the film “sweet and spicy”, last week it was announced that the Utah-based cinema chain Megaplex is refusing to show it because of its graphic content. It’s an overreaction if ever there was one, and Banks maintains her conscience is clear. “I don’t do anything in the movie that I wouldn’t let my mother watch,” she says, “and I don’t expose anything in the movie that I wouldn’t expose at the beach.”

True enough: her eventual coupling with Rogen is about as erotic as the sack of coffee beans they do it on. Still, it would be interesting to know what the First Lady would make of all this. As it happens, Banks met Laura Bush when Seabiscuit, the drama that she starred in opposite Tobey Maguire, was screened at the White House. “It was very insightful,” she admits. “She takes her job as First Lady very seriously. She considers her job to take care of the psychological and emotional health of the President of the United States. And that says a lot about what she thinks of the role of being a wife in general. I think she really feels that was part of her patriotic duty.”

The evening also afforded her the chance to spy on the outgoing President himself, not that he made much of an initial impression. “Frankly, George Bush was probably in the room for 15 minutes before I noticed that he was there,” she says, leaning forward in her chair conspiratorially. “But when you speak to him, he makes you feel he is a pal. He was very self-deprecating, very sweet and very interested. So you walk away going, ‘Yeah, great guy.’ I don’t agree with any of his policy issues, but I understand why he was a great candidate for president.”

Unlike Bush, Banks can’t afford to fail to make an immediate impression. Her decade-long career has consisted of small roles, albeit in large films, from the Daily Globe secretary Betty Brant in the Spider-Man trilogy to the bank clerk charmed by Leonardo DiCaprio’s con artist in Spielberg’s Catch Me if You Can. Judging by her latest work, however, Banks is now facing the prospect of major-league stardom. “I have no expectations for what’s going to happen,” she counters. “I hope it gives me a little more control over what I work on.”

She dubs herself “a sassy broad”, but Banks also confesses that she is “a goody two-shoes”, making her appearance in Zack and Miri...all the more odd. “Ah, but when it comes to profanity and sexual things, I’m pretty open,” she explains. So was she ever a bad girl in her teens? “I was a bad girl in ways that people aren’t comfortable with. I had a boyfriend when I was young. Let’s put it this way – if I have a daughter I’m going to lock her up when she’s 14. If I think about the things that I was doing when I was 14, I really hope my daughter’s not into them.”

Born Elizabeth Mitchell (she later changed her name to avoid confusion with the Lost star), Banks was raised in Pittsfield, Massachusetts. The eldest of four, she comes from a “humungous” extended family. “My mother is one of seven children, and my father one of eight. They are all married. They all have cousins. And none of them are in entertainment in any way, shape or form.”

Banks’s mother worked in a bank, while her father still works on the factory floor of General Electric. She describes her own route into acting – from San Francisco’s American Conservatory Theatre to a New York stage career – as “very traditional”.

It was while she was at college that Banks met her husband of five years, Max Handelman. They now run their own company, Brownstone Productions, with their first offering, a sci-fi action film called The Surrogates starring Bruce Willis, due out next year. With no intention to act in anything that she produces, Banks maintains that her company is a serious venture rather than a mere celebrity accessory. “I really want to establish a legitimate producing business,” she says. “I think when actors create vanity projects for themselves, it doesn’t lead to very credible producing credits.”

Working nonstop for the past year, Banks has another comedy, Role Models, due out in the UK in January. Playing the lawyer/girlfriend to Paul Rudd, it reunites her with the director David Wain, who cast her in one of her earliest roles, in 2001’s summer camp farce Wet Hot American Summer. “He’s one of my closest friends,” she gushes. “I adore him.” With the horror-thriller The Uninvited, co-starring David Strathairn, also in the can, it is little wonder that Banks is now planning to take two months off “and see what happens in the spring”.

At least it will give her the chance to spend quality time with her husband. “We’re pretty good,” she says. “We try and see each other every two weeks. We’ve been together a very long time so we are very used to not being with each other. You have to remember, most people go to work for eight hours a day and are away from their spouses. My husband and I, when we’re not working, are sitting at home hanging out together 24/7, so it’s good for us to be apart sometimes.” The way her career is going, such downtime will soon become a thing of the past.

W. is out now; Zack and Miri Make a Porno is released on Nov 14 2008

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