Seven years ago, Frances O'Connor was plucked from the relative obscurity of the Australian indie film circuit to star in Mansfield Park. It was, says the Australian actress, "a big leap", taking on a Jane Austen heroine under the watchful eye of the British acting establishment (Harold Pinter, Jonny Lee Miller and Lindsay Duncan among others), and she found the experience "a little bit isolating".
"It was the first time I'd worked outside my culture. You always think, 'I'll fit into English culture,' but working in it is different from watching it." Since then, O'Connor has donned several more corsets - for the BBC's Madame Bovary (a casting greeted by headlines such as "It's Sheila Bovary!"), where she was thoroughly romanced by a trio of English gents, Hugh Bonneville, Hugh Dancy and Greg Wise, and for The Importance of Being Earnest, in which she played Gwendolen to Colin Firth's Jack.
These days the 37-year old actress, who was born in Wantage and has lived in London for the past five years, has become something of an honorary Brit. "I do feel quite comfortable here," she admits. "There's always something comfortable about the English coming to Australia and vice versa." Although her natural tones are still unmistakably antipodean (with hints of LA and London creeping in), she must have the cut-glass English accent off-pat by now? "I still have to work at it", she demurs.
She is giving the RP muscles a work-out in her latest role, playing T S Eliot's first wife, Vivienne Haigh-Wood in Tom and Viv at the Almeida in London. Inspired by Edith Sitwell's throwaway comment at a party - "at some point in their marriage Tom went mad, and promptly certified his wife" - Michael Hastings's play charts the disintegration of the American poet's turbulent first marriage.
Beginning with a whirlwind courtship in Oxford, it chronicles Vivienne's increasingly erratic behaviour (her neurotic demeanour once led Virginia Woolf to liken her to a "bag of ferrets") and ill health, culminating in Eliot committing his wife to a mental asylum. Vivienne spent the last 12 years of her life incarcerated; Eliot never applied for her release (though she was sane by the end) nor visited, nor responded to her letters.
For all Eliot's attempts to pass himself off as a martyr to Vivienne's volatility (he reportedly wore greenish face powder during the most trying period of his marriage to enhance such an impression), his wife was instrumental in securing his success. Not only did she provide a way in to the aristocratic society he admired, but she was also a useful artistic collaborator, particularly on The Waste Land.
"After Tom left Viv I don't think his poetry was as good again. He became very conservative, it became very much about him showing he was part of the establishment. He never had that visceral edge to his poetry again. I'm sure that's because his life with Vivienne was so tempestuous and she really challenged him in terms of his writing," says O'Connor.
All in all, it's an ambitious choice for O'Connor's return to the London stage and to acting, having given birth to her son 15 months ago. She last trod the boards as Maggie in Cat on a Hot Tin Roof at the Lyric, London, in 2001, an experience she bemoaned at the time as being "seriously draining".
When we meet backstage at the Almeida she claims that she finds it easier to switch off from the on-stage turmoil these days - riding her bicycle to and from rehearsals and caring for her baby to "debrief". Dressed in an old sleeveless brown T-shirt, baggy-ish trousers and very sensible flat shoes, she looks a little thin. But the features so beloved of the period drama casting agent - pale skin, black eyes, upturned nose and the improbably wide cat-like mouth - are unmistakable.
Performing is in O'Connor's genes. Her mother is a musician and "her whole side of the family have a kind of theatricality about them". After completing a BA in literature she took a gap year travelling around Japan, teaching English as a foreign language, modelling and, intriguingly, singing in a Japanese band. On her return she enrolled for three "intense" years at the Western Australian Academy of Performing Arts, where Hugh Jackman was a contemporary.
On graduating, she landed parts in several Australian films - notably as the womanising lesbian, Mia, in the kooky Love and Other Catastrophes - but she considers Mansfield Park, her fourth film, as her big break. "Patricia [Rozema] wanted to cast somebody who wasn't English. I think she felt that if she cast an American or an Australian there might be an interesting energy," she laughs. "I was like, 'I don't care, I'm just glad you gave me the part.'" O'Connor's feisty turn led to the romantic lead in a raunchy Madame Bovary for which she was nominated for a Golden Globe. It remains her favourite role.
Hollywood inevitably came calling, first in the shape of Harold Ramis's remake of the Peter Cook and Dudley Moore film Bedazzled, in which she played the all-American love interest opposite Liz Hurley's catsuited Devil and Brendan Fraser. In Steven Spielberg's overblown AI she landed the part of the grieving mother who takes in Hayley Joel Osment's too-good-to-be-true robot child. It should have been a dream project, but O'Connor is hesitant. "It was umm... It was good but because it was such a big, high-profile job I found it hard to enjoy doing it in some ways."
Apart from a lisping, seductive turn in Ollie Parker's light-as-a-feather The Importance of Being Earnest, her subsequent films have been pretty unremarkable. And while her costume-drama credentials are impeccable, the perfect big-screen, contemporary piece has eluded her. But she has no qualms about being typecast: her dream role would be Emily Brontë.
At the end of her lunch-hour she apologises for being a bit "brain-dead". "The best thing about stage is that it does wake you up pretty quickly", she says ironically. "So hopefully I'll get my act together."
'Tom and Viv', Almeida Theatre, London N1 to 4 November (020-7359 4404) Media partner: 'The Independent'