Despite hysterics, Katharine Hamnett's new collection will take to the catwalk tonight. Interview by Shane Watson. Photograph by Ben Elwes
Katharine Hamnett is winding her long hair up on her head in a knot and then undoing it again. In the stray moments when her hands are free she lights cigarettes, picks up abandoned cups of coffee and flickers very slightly, like a racehorse in a lather. She is wearing a T-shirt imprinted with a black-and-white photograph of a Tibetan boy and the words "Release this child, Gedhun Choekyi Nyima" (the seven-year-old Panchen Lama now imprisoned by the Chinese).

"We've had a complete crisis with the collection", she says, locking on to me with her brown eyes. "I don't think we're going to have a show tonight."

Despite the usual show-time hysterics, Katharine Hamnett's autumn/winter `97 collection will take to the catwalk this evening, as it has twice a year since she went into business in 1979. Previously, she has shown her collections in Milan and Paris, but returned to show in London two seasons ago. At 49 Hamnett has become one of the British fashion establishment, albeit most famous for her anti-establishment views. She was the one with the round dark glasses who wore the slogan T-shirt, "58 per cent Don't Want Pershing", to her meeting with Margaret Thatcher at Downing Street in 1984. Besides the protest T-shirts (including "Stop Acid Rain", "Worldwide Nuclear Ban Now" and "Preserve the Rainforests"), Hamnett was an Eighties byword for strong, "intelligent" fashion. Wearing Hamnett was like wearing The Guardian, only much sexier. She pioneered workwear: those cotton drill separates described as the Army surplus look. She started the craze for billowing parachute silks, what Hamnett calls "the boiler suit thing" ("If I had a 10th of a penny for every metre of that stuff sold globally since then, I would be a billionaire"). She had a shop the size of a hangar in Brompton Road, designed by Norman Foster. While those less in the know were adding inches to their shoulder pads, Hamnett was laying the foundations of a cool, non-status-conscious dressing - tight and tailored but also pre-washed, pre-crushed and distressed. Famously she put condom pockets on boxer shorts, and said that "women buy clothes primarily to get laid", though she now says: "That was a joke. One buys clothes for every day and for most people that's a work situation."

The key to Hamnett's success was spotting the absence of clothes for the woman who knew what she wanted and didn't want to look like a bond dealer. "When we started it was all that kind of Fascist dressing; looking back, it all looks ghastly".

Katharine Hamnett now sells in 30 countries, and has an estimated turnover of more than pounds 100m, of which 40 per cent comes from the Far East. That includes licences, from underwear to umbrellas, and the eyewear that was launched here last autumn. Otherwise Katharine Hamnett Denim, the less expensive though not exclusively denim line, is the most successful. Though the clothes have changed through the years the image is essentially tough, sexy, rock chick (and guy). "I suppose inevitably it comes back to that," she says. "I quite like rock chick but I don't like groupie. It's an image that exerts a powerful hold over the Japanese market, even if it has ceased to have the same impact here."

The name Katharine Hamnett still suggests sex and attitude, largely because of the Denim advertising campaigns, renowned for their raunchy content, bordering on the pornographic. Shot by the likes of Ellen Von Unwerth and Terry Richardson, they feature couples half-way there, with close- up shots of pantie gussets, tongues in mouths, hands grabbing crotches. The latest campaign , by Juergen Teller, has the loopy aristo model Iris Palmer sprawled on a sofa in just a pair of silk shorts, and Katharine's own discovery, Imir, who works for her local north London taxi service.

Hamnett has always made a point of courting controversy, or perhaps just trying never to do what people expect. As a result she's a mass of contradictions. She's a smoker who opposes the pro-smoking lobby ("Who taught them how to do it? There's industrial money behind it"). She distributed "US Go Home" T-shirts at Greenham Common but now she's "pro deterrents". She refuses to answer any questions regarding her family (two young sons) and yet mentions them constantly. She is a woman, you get the impression, who through success has been able to indulge her every whim, however capricious. "I wanted to be an actress and I also wanted to be a trapeze artist," she says, flinging her arms around, whipping her legs over the side of the chair. "I'd like to have been an archaeologist ... mind you the field work scene ... I went to a couple of digs and just thought, fucking hell."

One moment she is wildly enthusiastic. The next her face crumples at the mention of her first taste of success. "My father used to say, "I wish I could live to 94", but he didn't," she says, tears streaming down her face. Somewhere in the midst of it emerges a picture of the stubborn, talented, highly-strung daughter of a defence attache, educated at Cheltenham Ladies' College, who "thought everyone would say I was mad, and I just thought, this is really annoying. I want to prove them wrong and so I just went for it."

You can't help but admire her nerve, her unfashionable tendency to bad- mouth the right people, her pigheaded approach to politics, however confused her motives. She is committed to an environmentally friendly policy throughout her business and has pledged to be using all-organic cotton by the year 2000. And she is still using fashion to get her message across. "It's difficult, because I think we've suffered the backlash for it. There were accusations of us using the slogans exploitatively." In fact Hamnett is a subscriber to the idea of giving a charitable contribution on items of clothing. "Now I'm afraid to get too involved in an issue in case I do it a disservice."

Even so, "Sanction China" was the message of her last collection, emblazoned in sequins across the model Sybil Buck's chiffon-covered chest at her London show.

Would she take her message on a T-shirt to Tony Blair at 10 Downing street? "I don't know. I mean they're so boring, aren't they? Who cares? I might." She leaps up in a new flutter of neurosis. "Have I made myself out to be a complete maniac?" she asks, and rushes off