London Fashion Week: Hot Pants

3.30pm Sunday: "Sorry to interrupt, but I thought you might be interested in my pole-dancing school." As ice-breakers go, it wasn't bad. Janine, a fabulous fox in skintight jeans and T-shirt, pulls a flyer from her Louis Vuitton hold-all and shoves it into my hand. "Gemini: the school of pole dancing," it reads, above a close-up photograph of a naked girl, her thighs neatly framing the image of a man relaxing in a plush velvet chair. Drink in hand, he gazes up at her, and no, he's not looking at her eyes. Gemini is "a school with a difference" where you can learn such skills as "pole tricks, table dancing, deportment, etiquette, fitness, stage presence, engaging a customer... all these things will help you gain a stronger confidence".

Janine is here to give just such a confidence boost to four young women who probably don't need much help in that particular department. They are the models Kate Moss, Leah (daughter of Rolling Stone Ronnie) Wood, Holly Davidson and Rosemary Ferguson.

It's opening day at London Fashion Week and at the Duke of York's Theatre, St Martin's Lane, rehearsals are in progress for perhaps this season's most eye-catching event. In two hours' time, Jemima French and the actress Sadie Frost – who own and design for the FrostFrench label – are scheduled to unveil their autumn/winter collection. But this is no ordinary fashion show. For while the industry has grown blasé when it comes to seeing beautiful women dressed in their smalls, seeing them strip off as they shimmy suggestively across tabletops is quite a different matter. Hence the presence of Janine, who has been "working" with the girls this afternoon and – if Leah Wood, on a table, gyrating frantically in and out of a pretty, tie-fronted dress reminiscent of Biba in its heyday is anything to go by – she's done a pretty good job. Frost's younger sister, the actress and model Holly Davidson, is also on frisky form, prompting the thought that she may have missed her vocation.

Ms Moss, tonight's star turn, looks, as always, more beautiful than is strictly decent. She lies on stage across a sheepskin rug in dusty-rose underwear and fluffy, pink, cashmere over-the-knee socks as if to the manner born. Still, she's nervous. "I'm supposed to be a catwalk model," she moans in the famous south London accent. "I'm supposed to walk up and down the catwalk sombrely. I'm not supposed to fall about laughing and take my knickers off on stage."

Tonight, however, she will do just that. Kate is Sadie's friend – and clearly, she's a very good friend indeed. After all, the world's most famous model doesn't need – or even want – to work the shows these days, and after ruling the runways for so long, who can blame her? "She's a bit nervous, I think," confides Frost. "It's not the same as us dancing around at 3am in the morning. There'll be loads of people watching."

That's for certain. Even before it began, this season's London Fashion Week came in for the usual pasting – no designers, no international press and buyers, no celebrities. For tonight's opening, FrostFrench will show that there's more to the British fashion capital than draughty old productions stuck out in deepest Shoreditch. So, here at the Duke of York's, they will be showcasing London's glamour quotient – glamorous, that is, in the very naive and sweetly idiosyncratic way that only the British fashion capital knows how. It may be freezing February outside on this quiet Sunday afternoon, but while the real world goes about its business, Planet Fashion is about to offer up a sex-and-shopping extravaganza that begs to be described as sizzling.

4pm: The hour draws near. "It's just supposed to be a laugh," Frost says, eager not to be judged too harshly.

Jemima French and Sadie Frost are both 35. They've been best friends since they were 15. They "grew up together" and "shared the same boyfriends". Since then, Frost's on-screen performances, marriage to Jude Law and celebrity friendships have made hers a name to conjure with. Still, being savvy and surprisingly modest, French and Frost feel that their label – founded in 1999 and therefore young by international-fashion standards – is still too green for a traditional fashion-show format. Instead, they are putting on a play, albeit one featuring a narrator rather than traditional dialogue. "Everything's meant to go wrong," announces Frost, just in case there are any drama critics in the house. Chekhov this ain't. Rather, it seems to be gearing up as the best-dressed – and most precocious – school disco the world has ever seen.

Featuring our four FrostFrench-clad lovelies – and narrated by the actress Lisa Faulkner, who looks way more fashionable here than she ever did in Holby City – the play tells the sorry tale of a group of young women, all in love with the same man. The villain of the piece is a love rat who takes out a different girl every night of the week, and our heroines are busy dressing up for just that occasion – tossing one garment aside after trying it in favour of another, as girls of a tender age are wont to do.

"Rather than the catwalk, we decided to show our winter collection in a different way," reads the programme note, in case anyone is feeling confused. "Hopefully you can see both the clothes and the concept of FrostFrench through the expression and feeling that the girls and the show portray." What are the clothes like? Well, there are pretty dresses aplenty, skinny jackets with smocking at the back and trousers so low they barely graze the navel and, of course, the saucy underwear that made the label's name. Fancy a pair of knickers with "DIAMONDS" studded across the back in rhinestones? You're in the right place.

"We just wanted to avoid the catwalk," explains French, who is five months pregnant and wearing a grey cashmere mini dress. "We're taking baby steps. The collection's grown so fast, we've doubled our production every season, but it's not fashion in any serious sense, it's much more spontaneous than that."

What the FrostFrench label represents might be called the Stella McCartney School of London Fashion – cool girls in sexy clothes but not, as French puts it somewhat bluntly, "in a tits-out kind of a way". But whereas McCartney's label is both designer-label expensive and shown alongside the great and the good, FrostFrench has taken a different, more surprising path: producing cheap and cheerful clothing that isn't intended as anything other than light-hearted and certainly won't break the bank. Past hits have included knickers printed with the face of a cat, which purred obligingly when pressed, and trousers so low-slung that they were plain rude.

"We were the girls who always said the wrong thing, wore the wrong thing... we're both nerds really," says Frost of their partnership. "We were both pregnant when we came up with the idea and we were bored. It started in a very small way, making the odd thing for our friends. There is a hole in the market, though. There are wonderful designers and then there's the high street, but there's a gap in the middle."

4.30pm: The models are in hair and make-up. Kate Moss – a consummate professional if ever there was one – has apparently practised her show-opening striptease some 50 times.

Tension is beginning to mount. Despite the classroom atmosphere and the rehearsal banter, tonight's show is, after all, a commercial endeavour. Though it's been put together in just three weeks, an awful lot hangs on the next couple of hours. "Things are supposed to go wrong," French says again, though this time one feels that the lady may be protesting too much. "Kate only only got back from New York today ... and I'm worried that no one will be able to see the clothes ... but the label's all about personality. You've just got to have confidence."

5.15pm: Anita Pallenberg, the legendary rock chick muse of the Rolling Stones, arrives in a black fedora looking suitably scary and utterly great. So does Mario Testino, who doesn't leave home for just anyone.

Finally, Frost's husband, Jude Law, is ushered to his own personal box, looking down from on high.

6.15pm: The lights go up, fashionably late, and each girl in turn takes centre stage. Kate Moss – as befits her status – is first, pulling on a tiny mini skirt and thigh-high boots for her date. But she doesn't like her look, and duly disappears behind a screen – shades of the The Graduate – throwing off her clothes, naked arms and legs peeking provocatively from behind. Rosemary Ferguson is next, stripping off a denim boilersuit in favour of something a little more comfortable. Leah Wood gets the prettiest dress, and. given the frenzied enthusiasm with which she pours herself into it – spurred on by Dad roaring whoops of approval from the gods – this seems only good and proper. And Holly Davidson wins the award for Best Amateur Erotic Dancing The Fashion World Has Ever Seen.

As the proceedings draw to a close, narrator Lisa Faulkner assures us that these girls "aren't stupid". They know when a man's messing them around and will exact their revenge. "How? Now that would be telling." There's clearly no room for shrinking violets in the world according to FrostFrench. Like four modern-day Monroes, the girls link arms for the finale, cavorting to strains of "Diamonds Are a Girl's Best Friend".

7pm: The show's over, and we file back out into the cold again. I confront the West End traffic, no longer feeling remotely like a modern-day Marilyn Monroe. Suddenly, silk knickers, camisoles and skimpy cotton dresses seem a world away again. It's February! Are these people mad?