Until now, Imelda Staunton has been recognizable—well, sort of—as the British character actor who seems tiny and round and bustling: the nurse in Shakespeare in Love or the kindly cousin-by-marriage in Sense and Sensibility. Until now. Mike Leigh's Vera Drake has arrived at movie theatres in the United States, and Staunton's towering performance in the title role is shaking up critics and discerning audiences. She plays an Everywoman—wife, mother, good neighbor, house cleaner—who happens to be an abortionist in 1950s England. The film takes no sides; it's so powerful, however, that a few critics have termed it heavy-handed—several for each side. But everyone agrees this is Staunton's best work to date, certainly one of the best performances of the year, earning her a British Independent Film Award nomination and the Venice Film Festival's Volpi Cup as best actress.

Leigh's methodology began with casting, then months of improvisation, and then a finalized script derived from the improvisation. The film follows Vera over a downward arc. We first see her as a fulfilled family woman: working several jobs but finding satisfaction in doing them, loved by her husband and grown children, beloved by her neighbors and those she tends on the side. But one of her jobs is performing abortions, which were illegal at the time. An infected patient leads to Vera's arrest, trial, and imprisonment. Near the film's end, for minutes on end, tears flood out of a mute Staunton's eyes. The actor may have been a two-time Olivier-winning delight of musical theatre, Mary in Peter's Friends, the voice of Bunty in Chicken Run; but we've never seen her like this.

Leigh apparently had—at least in his mind. At the time he telephoned her to invite her to participate, she says, she had been searching for an intense creative experience. The two met, they did what each calls "a bit of work"—he refuses to divulge the exact process he has developed for auditioning actors—and he called her back 24 hours later.

In person she's young-looking and sweetly groomed. In Vera Drake she looks elderly and ground down. Of course, she explains, she was allowed no makeup. "And that period aged people. We improvised for six months. We improvised going through the war. They were working people. In a way, the makeup was done by Mike Leigh. We lived those lives." She says she researched only what Vera would know, creating her from the time she was born—a girl without dreams, who left school at 11 and worked in a laundry.

It was Staunton's first foray into improvisation, and the process spoiled her for other projects. "You're so the character that by the time you're being with the [Drake] family and doing it all, you're fully formed. And things are still developing even while you're filming. But you're not just an empty vessel making a noise. You are that character, speaking what she would say."

Staunton accepted a role in the London production of Michael Hastings' Calico as soon as she finished the film. "It was a mistake," she says. "I should have waited, silly woman. But I thought, 'If I don't get another job, I'll plummet.' It was worrying about the fallout from doing the work with Mike. It was to do with keeping going. I thought I'd need a job that would make me get up and 'off we go.'" It wasn't quite depression, but she was feeling aftereffects. Performing the play, she found her mind going blank onstage. "Because I didn't really believe what she was saying," she explains. "I spent a year creating, inventing lines, with Mike. And I'd think, 'Why would she say that?' But it was a new play, and I love new writing."

Indeed ask Staunton what great roles she'd like to take on, and she refuses the classics. "Funny, I've never been that sort of actress, saying 'Ooh, I want to play this,'" she says. "I love new writing. There are plenty of actresses who want to do the classics, and they'll do them a lot better than I will. But comparisons are odious. You've got people going, 'Imelda's not … but I remember when so-and-so played the part.'"

As a child, Staunton participated in school plays, but she also had an elocution and drama teacher for after-school classes. "And she was absolutely adamant that I audition for drama school," the actor recalls. "I didn't know you could go to drama school." Staunton auditioned for three but was accepted at only one: fortunately it was RADA. "Going to RADA at 18, I just lapped it up," she says. "And then I had the luxury of having six years after being in drama school going 'round repertory companies, having an apprenticeship, being in The Boy Friend at one end of the season and playing St. Joan at the other end, to doing Electra, to doing Cinderella, and being able to do the parts not particularly well but giving it a go and getting the experience of doing it." She then joined Richard Eyre's company at the National Theatre in 1982, in Guys and Dolls and The Beggar's Opera. Radio and television followed. Last to arrive was film work. "And only in the last three years, maybe, I've felt as comfortable in film as I did onstage," she admits.

It's rare to find a performance as flawless as Staunton's: created with no false words or forced gestures, no obvious effort, but with a principled sense of who Vera is. In the film, Staunton also occasionally does what only few actors dare to do: nothing. And this makes for mesmerizing work.