There's no boxing Helena

It's Queens R Us in the Bonham Carter household. Buoyed by a year of royal roles, Helena no longer has to mind her Ps and Qs over tea. The empress of the corset tells Tara Bradyabout her dress sense and playing the late Queen Mother in The King's Speech

‘WHAT I really treasure are the young women who come up to me and say ‘thanks for allowing me to be different’,” says Helena Bonham Carter as she dashes about her hotel room. “I had this brilliant piece of fan mail recently. I rarely read fan mail, I’m afraid. I should be much better about reading it and answering it. But I remember this one because it was a list of 20 ways that I had made a difference in her life. So it read: ‘It’s all right for me to wear what I want. It’s all right for me to be myself. It’s all right for me to have short, thick legs.’ Hang on. Is it really? Short, thick legs?” She gestures toward the door and makes for the loo.

That's when her phone buzzes. Blast. I've already looked down and noted that the incoming missive is from Nigel Slater when I realise what I've done. Well I can't possibly ask about her role in Toast, the Nigel Slater culinary biopic now. She'll think I've been prying. She'll think I'm not to be trusted with her belongings ever again.

Damn it. Until this act of accidental treachery we were having a perfectly nice conversation comprising mumsy, over the fence topics – she likes the stuff in All Saints, though Selfridges is very handy; she notes the importance of having her mother down the road; she lists courses she might do to help keep the children occupied during the holidays.

But perhaps I’m not entirely to blame. It is typically unguarded of Bonham Carter to leave her mobile phone with a member of the press.

Ever since her precocious movie breakthrough, aged 19, an English rose par excellence in Merchant Ivory's A Room with a View,Bonham Carter has proved the type to wear her heart on her gothic, banquet-cut sleeve.

Everybody knows that she lived with her parents until she was 30. Everybody knows too that she didn’t bother with boyfriends for years.

“Acting is so dependent on your own emotional experience,” shrugs Bonham Carter, as she carefully alternates between an espresso, juice and sparkling water. “You might be miscast in something or get unlucky, but generally you’ll get better at it as you go on. So let’s just say I couldn’t have been any worse at it than I was during my time as a corset girl.”

For all her protesting, Bonham Carter has been shaped by that whalebone garment just as surely as any of her 19th-century ancestors were. Corseted Henry James and EM Forster adaptations made her a household name and earned her an Oscar nod in 1997. The constricting garment seemed to suit her; she was an exquisite, definitive Ophelia opposite Mel Gibson's Hamletin 1990, but merely a standard-issue contemporary love interest for Woody Allen in 1995's Mighty Aphrodite.

She soon rebelled (she is, after all, the grand-daughter of British prime minister HH Asquith) and gleefully bit the hand that fed by turning out for David Fincher's Fight Clubin 1999.

She still laughs at the recollection. “Aren’t I awful?” she says. “Such a mean thing to do to people expecting nice frocks.”

Since the turn-of-the-millennium, the onscreen and off-screen muse of director Tim Burton (the pair have worked together on eight films, including Alice in Wonderland, Charlie and the Chocolate Factoryand Sweeney Todd: The Demon Barber of Fleet Street) has developed the same kind of relationship with a corset that Mark E Smith maintains with rockabilly. Even when she's away from her partner's similarly mischievous milieu she can be found bastardising garments of the romantic era as Bellatrix Lestrange in the Harry Potter franchise.

“I suppose with everything and anything you find yourself becoming more at ease with who you are as you get older,” says Bonham Carter. “I like my goth dolly thing. Tim helps in a way. Not that he controls what I wear. He just laughs when he sees me and calls me Minnie Mouse at home. But he will make me aware when I’m wearing seven things too many. He has eyes. They happen to be useful for directing and noticing when your wife has gone overboard.”

She and long-time companion Burton share three adjoining north London homes – one for her, one for the director, one for their children Billy Ray (7) and Nell (3) – and a profound fondness for dress-up and play.

They have earned a fine eccentric reputation as Hampstead’s answer to the Addams Family.

“I like to have fun getting dressed,” she says of her famously spooky trousseau. “I approach it like any other costume, really. My daughter is exactly the same. We tried to civilise her for nursery school, but she went every day as a different person – skeleton, princess, fairy, princess-witch, then back to the skeleton. Getting dressed up is fun, just as fashion isn’t fun. Fashion is a set of rules that nobody can live up to.”

The actor is certain, moreover, that her dressing-up policy can be successfully extended to all domestic situations.

“We love spending passages of time in different places,” she says. She uses a sing-song voice that makes me think we’re about to roll dice to determine the best way to spend the rest of the afternoon.

“I love Dublin, for example. And I love that you’re a bit of a gypsy when you’re an actor, and you get to play house somewhere else. But I couldn’t live anywhere but London. I love our house. I love being close to my mum. It feels right for Tim, it feels right for me and it’s a great way to bring kids up.”

For all the couple’s combined efforts, either together or in their regular triumvirate with Johnny Depp (a Burton regular and a godfather to their son), there is, Bonham Carter says, no collaborative process to speak off.

“Ha. There’s never a word out of Tim,” she says. “I always presume I won’t be needed and I’m always a bit surprised when it happens.

"Sometimes, of course, it's not his choice anyway. On Sweeney Todd, for example, Steven Sondheim had final say. I also bring a lot of it home, which drives Tim quite mad. I play around with the accent until everybody is sick of it. Mrs Lovett from Sweeney Toddwas the best, because she's left a residue of pie-making and singing in me. That's why our house is a bit like Queens R Us just at the moment, between doing the Red Queen and the Queen Mother. Everybody's playing along: I can order tea without even saying please."

At the time of writing, Bonham Carter has already been shortlisted by the Screen Actors Guild and several major critics circles for her recent role as the iconic British royal (as opposed to the made-up Lewis Carroll one) in The King's Speech. An uplifting heritage drama inspired by the relationship between Britain's King George VI (played by Colin Firth) and his speech therapist Lionel Logue (Geoffrey Rush), the film marks another contrary return to costume drama for its only female headliner.

"It was weird and lovely, because I worked with the same costume department that was on A Room with A View.Mind you, it wasn't the most fun wardrobe. I mean the queen mum, well, she was fond of her furs – never the best look. But she was very good at getting that powerful big-shouldered shape. So I had to think of my body as a huge triangle and my head as a circle. She had this completely round face and head. I don't really look like her, but I needed to get that silhouette right so that I was recognisably her just the same."

It is, she says, an odd, prestige project. “One feels it ought to have been a movie before. But it’s a subplot really. History has always been keener to report the scandal of Edward and Mrs Simpson. The Prince of Wales, whatever his shortcomings, had been really popular when the film is taking place. It was extremely doubtful that George, or Bertie as he was called, would be accepted by the British people.”

For this reason she’s far less inclined toward the traditional fluffy view of her character’s historical correlatives. “There is a huge amount of sentimentality about the Queen Mother. “And there’s a huge amount of respect for her. She did a lot for that family, particularly during the Blitz and other crises. She was quite indomitable and good for PR. She had to be pretty steely in order to survive quite so long.”

At 44, Bonham Carter wears her exotic French-Spanish-Jewish heritage well, but is far more likely to put her mug to work as nasty old Enid Blyton than as a fragrant romantic heroine. It hardly matters: she can’t bear to watch herself on screen anyway.

"No, no, no," she insists. "I don't like watching myself at all. Mind you, I saw some of A Room with a Viewrecently, when I had to dust it off for some friends. I didn't mind that so much. I don't think I was much of an actor back then, but I think I've changed so much from my younger self. It was like looking at a person from a bygone era." She laughs. "A person from a bygone era of corsets."

* The King’s Speechis on general release