'Fat Pig': Kelly Brook does high culture

I don't understand why Kelly Brook, the former lingerie model, sometime actress and jobbing TV presenter, wants to take on the role of Jeannie in Neil LaBute's Fat Pig, currently on in the West End. Jeannie is a terrible, humourless wretch. When she discovers that former lover Tom has spurned her for an obese librarian, Helen, Jeannie expresses her disappointment by shrieking, going red in the face and saying bitter, resentful and angry things.

To make her sympathetic would test the experience and range of Dame Judi Dench, let alone Kelly Brook. And I'm not sure that Brook, as we know her, is wise to play, even ironically, the sort of woman that we suspect she might actually sort of be: celebrated almost exclusively for her looks and, perhaps (you never know) a tiny bit shrill?

Is the role simply a cameo? Is her agent having a laugh? Would this be the same agent, by the way, that scored Brook the gig of an advert for Sky Plus, the premise of which is that if Kelly Brook can work out how to use Sky Plus, anyone can?

Neil LaBute disagrees with me on every level about this. As does Brook. They exchange glances and make slightly appalled faces when I suggest that Jeannie is shrieking and unpleasant. No, no, they say: she is sort of the heroine of Fat Pig. It's Tom who's the villain of the piece; if Jeannie's a bitch, it's because he drove her to it.

"Jeannie is completely frustrated," says Brook. "She's been committed to following a relationship with this guy, he's been giving her all these false signals, he's not being honest and straightforward and saying, 'Look, I don't want to see you anymore'; he's just hoping she'll disappear. She's a very strong character and she's sure about what she wants and she's got strong convictions about what she wants.

"And to meet someone who's a bit wishy-washy and doesn't really know what he wants, it's, like, you know, he should just tell everyone that Helen is his woman and tell Jeannie that he's made this choice about who he wants. He should be a man about it, but he's not. So for me, the villain in the whole play is Tom, not Jeannie."

Wow. OK. But then, a feminist interpretation of the play would probably find that Jeannie was a heroine, too. Any post-feminist would watch the play and wonder why Jeannie doesn't just make a "Whatever" sign with her thumbs and forefingers when Tom announces he has a new girlfriend, and walk out, not bothering with all that cringe-making, defensive "You're an asshole" stuff.

Anyway, as well as thinking that Jeannie is something of a feminist paragon, LaBute and Brook also both believe that Brook playing her is a brilliant idea. I suppose, if you interpret the role of Jeannie as they do, it is.

"It's an incredibly smart move," says LaBute. "This role plays to all of [Brook's] strengths. Kelly's a perfect extension of something that I've been working on for about 10 years in terms of casting. It's interesting to cast people who are attractive and have a certain personal profile, and put them in roles that people find confronting – they want to like you but you say things that they find repellent, so you make it very hard for them."

For Brook, it's also more personal than just another line on her CV: "I can relate so much to Jeannie. If you have been celebrated for being thin and beautiful, and got whatever you've wanted because of that, and then you get rejected anyway, that's an amazing lesson to learn. A lot of young beautiful girls haven't been through that.

"So I'm lucky that I have – I know what it feels like to be rejected, and it's a shock. And you're, like, 'What? How can you not love me anymore?'. But it's part of life and it happens to everyone at some point – and it's scary when it comes along later on in life, I have to say! And I think that's what Jeannie's experiencing. She's 28 and she's thinking, 'Oh, is this what it's going to be like from now on – a string of disappointing men?'."

All three of us sit, perspiring quietly, in an airless, windowless room in the basement of the Piccadilly Theatre, which is decked out in red velvet, gold twiddly bits and a huge mirror – a bit like a prison cell designed by Marie Antoinette. Brook sits on the sofa, a life-sized doll in her proportions and make-up and expression; next to her is LaBute, a large, hirsute, mostly stony-faced New Yorker, dressed head to toe in black.

I'm not sure to whom Brook is referring when she says that she has been rejected, but I would imagine that it's her ex-fiancé, the Hollywood actor Billy Zane. I have to guess because her publicist, before the interview, tells me that any questions "about that" are "strictly off-limits". Brook and Zane lived together for a few years in LA, then came to London, but it all seemed to fall apart and he went back to America and she stayed in London.

Now Brook has a new boyfriend called Danny Cipriani, a rugby player who, at 20, is eight years her junior and is most famous, as far as I can tell, for posing naked with a rugby ball held over his crotch. Anyway, the tabloids cannot get enough of the pair of them, and Brook and Cipriani are photographed daily by the paparazzi.

"It is a bit of a roller-coaster ride at the moment," says Brook, cheerfully, about the tabloids' interest in her. "Having photographers waiting for you on your doorstep is a bit frustrating, but I've been doing this long enough to know that next month, they'll be after someone else."

Brook is entitled to sound like a weary old hand – she has been at this fame thing for at least 10 years. She first became really famous when she presented The Big Breakfast as a replacement for the much-loved Denise Van Outen. She was only 18, and one of the production crew leaked an internal memo to the press that said that difficult words should not be used on the autocue because Brook was likely to stumble over them. The leaker of the email was fired, but from then on, Brook was perceived as being pretty dim, a broadly incorrect assumption that nevertheless persists.

It's true that she doesn't dazzle with her wit and clarity of thought, but there are many girls who are as beautiful and shapely as Brook, and time and fortune is not kind to all of them, but they are kind to her. Call it intelligence, or luck, or whatever you like, but Brook has got staying power. She puts it down to a good, old-fashioned positive mental attitude.

"I write myself a little wish list and think, I don't know, maybe I'll get around to doing that one day... and somehow the universe hands it to me. I don't know how it happens. I just put it out there and let it go, and it comes back. I've been living my life like that book, The Secret, long before it came out. Thought manifests, so you've got to be careful what you wish for!

"Sometimes, things don't happen overnight – it takes two or three years, but you've just got to be specific about what you want, have a bit of faith, and things do happen for you."

She's certainly not doing badly. She may have only lasted six months on The Big Breakfast, but, as well as being constantly voted on to FHM's top-100 list of sexiest women and being snapped by David Bailey, she has her own line of lingerie and swimwear, and her film and television roles have included a part in the hit US TV Superman spin-off, Smallville, success on Strictly Come Dancing, and a stint presenting Celebrity Love Island.

I am the same age as Brook and, frankly, I wonder what I've been doing with my time.

When it comes to Fat Pig, she will doubtless boost ticket-sales, which, at this financially rocky time, will be welcome. She has a bikini scene towards the end, you see, and merely the rumour of Brook's fabulous figure being on display would be more than enough to double ticket sales.

Brook has experienced plenty of people staring at her in swimwear before – all her adult life, I imagine, but also, professionally, when she was a model; but what about on stage? Isn't that different? She makes a face: "It's just like being on the beach, really. I don't mind."

LaBute reminds her that she finds doing the curtain call in her bikini a bit awkward. "Oh yeah, that's true," she says, blithely. "The only problem with it all is practicality – I've got to bow in the bikini so, you know," she says, deadly serious, "it's got to be the right bikini."

'Fat Pig' is at the Comedy Theatre, London SW1 (www.thecomedytheatre.co.uk), to 22 November