The Bonham Carter who now slumps on a sofa in a rather less desirably located hotel off Oxford Street is, at 31, 12 years older. Almost everything that has happened to her in the intervening decade can be traced back to that debut as Lucy Honeychurch. The blood in her veins is an exotic European cocktail, but the combination of two more Forsters, a couple of Shakespeares, and five films set wholly or in part in the imaginary English landscape we call Italy have embedded her in our imagination as an English rose - and an undeflowered one at that. Elizabethan or Edwardian, she became every casting director's favourite dowdy, somewhat modern, often gamine heroine sitting on the live volcano of her own suppressed sexuality, wondering where the rumbles were coming from.
Little acknowledgment comes the way of actors who dislike this kind of ubiquity, or reliability, or apparent narrowness of ambition. When I asked her agent for a complete list of her credits (21 movies, seven television roles, five appearances in the theatre, and four on the radio), at the top of the print-out was a single lonely entry: "Best Actress Genie Awards, Canada 1996 for Margaret's Museum". No one, apart from Canadians, gives her awards, even when she's in films that win barrowloads of them. Indeed, no one seems even to bother to wonder whether she is actually any good or not. She is just there, part of the furniture of our cinema-going lives. So, can Helena Bonham Carter act?
In many ways hers was a classically American initiation, which is to say thoroughly unclassical. Her face was spotted by Trevor Nunn in a magazine, he cast her as Lady Jane Grey (Lady Jane was released, discreetly, after A Room With a View), and she's done it on the hoof ever since. If you measure actorly merit in stage credits, she'll never bowl you over. After a small handful of provincial roles early on, plus one ("miscast") West End appearance in Trelawney of the Wells, plans to go back are at best unformed. "I couldn't give a fag about this thing, 'Oh well, real discipline, real acting happens on stage'," she says. ''But I did enjoy it. And I would go back. But you have to commit yourself for eight months and, frankly, the dosh is nicer in film. And partly, I think, why go and do it if you're just going to be really not given the benefit of the doubt, because of having had it too easy in some people's eyes? It's too tiring after a bit. You just think, I'm not going to lay myself open yet again."
In film, the closest she has come to a genuine accolade was when Woody Allen cast her as his wife in Mighty Aphrodite. Though he'll never win awards for acting himself, Allen's standard practice is to surround himself with talent, and it was Bonham Carter he hired to turn in an impersonation of the no longer available Mia Farrow. And she actually did it very creditably, right from the first scene in which a quartet of wealthy Manhattanites sit around a restaurant table introducing us to their neuroses. ''It was an impersonation,'' she concedes. ''He left it up to me whether I wanted to play it English or American and I thought there was no doubt I'd end up talking American because he likes to have this overlapped and repetitive waffle. I made a vow to myself: Don't sound like Mia Farrow, and by the end I was saying, Oh my God, I'm beginning to sound like Mia Farrow. That experience was certainly like no other."
Buoyed by this foray into the 20th century, Bonham Carter has begun to test her range by choosing parts of a type not normally associated with her. Whereas before she would callowly accept every period role offered, a growing boldness in her choices has gone hand in hand with an understanding of her own market value. When she says, "You're always asked as if it's always a luxury that you can pick and choose your role, whereas the fact is that you're lucky to be offered them in the first place,'' she scrupulously adds that, "that was certainly more the case early on."
Among her recent challenges, Margaret's Museum found her bumping off her neighbours in a remote Nova Scotian mining community. In The Revengers' Comedies, the film version of the Ayckbourn play which was shot last autumn, she is the sassy heiress Karen. In The Theory of Flight, which she is currently filming in Wales, she has ambitiously taken the role (opposite her boyfriend Kenneth Branagh) of a wheelchair-bound victim of motor neurone disease who is losing control of her speech. And most daringly of all, she took a role in Portraits Chinois, a thoroughly French ensemble piece directed by Martine Dugowson, which opens this week. Only George Orwell's Keep the Aspidistra Flying, in which she plays the sensible girlfriend of an advertising copywriter (Richard E Grant) who wants to give it all up to write bad poetry, was "not very demanding".
The list of British actors who have performed competently in another language is not long. You'd think Bonham Carter would have an advantage, French being literally her mother tongue. In fact it would have been more useful if she hadn't grown up speaking her father tongue. Dugowson, who after her hit debut Mina Tannenbaum was free to cast the net wider, confirms that when Bonham Carter accepted the role "she almost didn't speak French at all. She had the language in her, but didn't practise. But when I met her we did readings of certain scenes from the role and I saw that with work she could do it." "The only problem at times," adds Bonham Carter, who had to put herself through a series of language courses, "was that we were encouraged to improvise and sometimes I hadn't the foggiest idea where they were going, particularly with the slang. I'd just carry on and afterwards say, 'I've absolutely no idea what's going on'."
To explain away the merest of accents, the character she plays is English, but has gone native. Ada works as a designer in a leading Parisian salon, lives with her French script-writing boyfriend, and wonders whether to terminate a pregnancy that would otherwise yield an undoubtedly French child. Her friends, whose comically emotional lives we follow over the course of two years, are French. Dugowson, who co-wrote the screenplay with Peter Chase, has none the less chosen to play on Ada's Englishness. "It was important to distinguish her character from the others, to give her a strangeness. She had to be childish and hard at the same time. She had to have some blockage. She has a very special way of acting that is not the same as the French. It's more marked. She plays a little like an Anglo-Saxon, like Katharine Hepburn. We have a picture of an Englishwoman that is a little eccentric and not very sexual."
While daringly different, in other words, the role also finds Bonham Carter on familiar ground - buttoning it all up again. It comes as no surprise to learn that Dugowson wanted to work with her ever since seeing A Room With a View. In one comic scene at a villa in Corsica, Ada and her old pen-pal Yves talk deep into the night while in her bedroom Yves's wife Nina goes spare with jealousy, on the very French assumption that opposite sexes don't simply talk at two o'clock in the morning. If she'd seen Bonham Carter's other films, she'd have known there was no cause for concern. By no manner of means could Bonham Carter be described as hot to trot. This was clear from the beginning: even as Lucy Honeychurch finally gave into passion in that famous clinch with Julian Sands at the close of A Room With a View she was trying to read a letter over his shoulder. In Bonham Carter's roles, the body is subordinated to the mind. It wasn't especially flamboyant casting that found her playing Santa Chiara to Mickey Rourke's St Francis of Assisi. She doesn't play sexual conquistadors. "There have been parts," she says, "that have come my way which are more sireny or more obviously sexual. But I just haven't chosen to do them because I didn't find them very interesting."
Things are slowly changing in this area too. In The Wings of a Dove, directed by Iain Softley, Bonham Carter plays the dazzling Kate Croy, and in a scene you won't find in Henry James's template she undresses first herself and then Merton Densher (Linus Roache). She has actually been there before - she once played a stripper in a Granada film called Dancing Queen - but is "sure that much will be made" of the scene. "I am required to show the whole and utter object. The whole doo-dah. The full monte. In quite a long lingering take ... although they said they'd recut it. I've never had a problem with the idea of doing nudity as long as there's a reason for it. I was very wary of it being in any way voyeuristic. But the scene as it is is not really about the nudity, it's more about the emotional vulnerability."
It's also, one suspects, about closing a chapter in Bonham Carter's career. Her apprenticeship, acting in the shadow of dames and knights and the extensively stage-reared, is now over. Nunn's Twelth Night, while not a great film, brought confirmation that she can now hold her own against the massed ranks of thespians, even outshine them by underperforming. Where Imogen Stubbs's Viola worked overtime, Bonham Carter's Olivia let the camera do the hard labour. Put her next to a company of French actors, though, and it's clear she still has some ground to cover. While she rummages through her box of facial tricks, they hold to the school of film acting that says, as it were, "moins est plus".
"I'm getting much less self-conscious as an actress as the years go by," she says, "but I've always felt comfortable in front of a camera. It's just like something's watching you and you know what it can pick up. It's a very intimate relationship. It's the opposite thing from stage acting, where the energy is projecting out. In front of film you have to let it in, and be relaxed enough to trust in it. You have to be very narcissistic in one way. Not a vanity thing, but just think you are interesting enough to afford not to do anything, so you can let things come rather than force yourself to be constantly doing something because you're frightened to be boring."
There's a scene at the end of Portraits Chinois where all these precepts are perfectly enacted. Ada has long departed her job at the salon. Her patron is dead, and a younger protegee has assumed control. After a fashion show Bonham Carter nostalgically sneaks up to the atelier for one last glimpse of a life she has left behind. She thinks she sees the ghost of her old boss, and the camera, swinging slowly round, holds steadily on her luminous face as emotions flicker imperceptibly across its suddenly fresh and unfamiliar landmarks. When she turns her head away the light catches the tears welling in her eyes. This is film acting in its absolute essence. The longer Helena Bonham Carter goes on exploring, the more guided tours there will be like this one, deep into the souls of the women she plays.
'Portraits Chinois' (15) is released on Fri.