Trinny and Susannah: Frock Stars

The television fashion gurus Trinny Woodall and Susannah Constantine, the women who tell the nation what not to wear, must be feeling a touch of schadenfreude this Christmas. A mere two years ago, with their detractors sneering that there was no money to be made in offering advice, the duo's fashion website, Ready2shop.com, crashed and burnt, taking £10m of venture capital with it. Now What Not to Wear, the book to accompany Trinny and Susannah's BBC2 cult fashion makeover series, is the Christmas No 1 bestseller. Since its September release, it has shifted 246,486 copies and rising, crushing rival TV lifestyle "brands" Jamie Oliver, Delia Smith, Alan Titchmarsh and the sainted Nigella Lawson in the process.

At £12.99, that's a turnover of about £3.2m. The publisher, Weidenfeld & Nicolson, is confident the full 670,000 print run will sell out within months, with sales of about £8.7m. That confidence is reflected in the seven-figure, three-book deal it offered the pair last week.

For a fashion book – and a hardback at that – to top the bestseller list is extraordinary. Just as impressive is the fact that, in presenting fashion on TV, it took two abrasive upper-class women to get the balance right between authority and the common touch. Susannah, a former girlfriend of Viscount Linley, can trace her family back to 1066, though her father's fortune came from property and shipping. A reformed Sloane Ranger, the 39-year-old is a mother of two and married to the Danish entrepreneur Sten Bertelsen. Trinny, 38, is the daughter of a banker and ran with the Hugh Grant/Liz Hurley/Henry Dent-Brocklehurst set before marrying a financial adviser, Johnny Elichaoff. Ostensibly, both have the cvs to gain entry to the Royal Enclosure rather than the hearts of the nation.

To understand their appeal, one has to study their predecessors. In the 1980s the BBC's Clothes Show was the first and last time television found a winning formula for fashion. But even in its heyday, insiders were calling the presenter, Jeff Banks, "the Jimmy Tarbuck of British fashion". Attempts to make fashion accessible but not hopelessly naff on television have failed. Channel 4's Slave was cool but couldn't escape the specialised-audience-ergo-slim-ratings late-night ghetto. The gameshow/makeover hybrid She's Gotta Have It cooled once its presenter Liza Tarbuck left the series.

Where Trinny and Susannah have been smart is to take sides with the viewer against the tyranny of high fashion. Constantine admits in the preface to the book that she's got "a body beyond redemption" and "tits way too large for human handling". Trinny says, "We know how we feel about our own bodies. The things we dislike. I had years of acne. I've got no tits."

Another major key to their success is the way in which they complement one another. Just as you can't imagine separating the individuals who make up other TV double acts – Laurence Llewelyn-Bowen and Diarmuid Gavin (Home Front) and Alan Titchmarsh and Charlie Dimmock (Ground Force) – so you wouldn't want either of the girls alone. Without Susannah, Trinny is too whippet thin and chic to be approachable. Without Trinny, Susannah lacks glamour. It's a delicate balancing act that could alienate viewers if it wasn't finely tuned.

Their "cruel to be kind" format is extremely well timed and the introduction at the top of each show intentionally provocative: "There are things not even your best friends will tell you. But we're not your best friends. And we will."

Yet every participant in the show, from helpless single mother of three or housewife gone to seed, has looked 1,000 per cent better after the Constantine and Woodall treatment. The public realises that their candour isn't cruelty. It is an antidote to all those glossy fash mags peddling dresses you can't afford on models with bodies you'll never match.

Their approach to the female body is distinctly gym mistress. Chapter headings in the book read like a playground taunt: "Big Tits", "No Tits", "Big Bum", "Saddlebags" and "Short Neck" to name a few problem areas. As well as savagely honing in on their victims' faults, often by grabbing haunches, bums, tums and tits and shaking them like a bulldog's jowl, Trinny and Susannah also demonstrate "problem areas" on their own bodies to camera.

It is a clever device to soften the harshness of their judgements about the rest of us. Harriet Quick, features editor of Vogue, says: "You can't imagine the number of fashion programmes that don't get past the pilot stage because the presenter alienates the viewer. Trinny and Susannah are direct but approachable. They are honing in on a woman's body shape and figuring out how clothes can work for you, drawing you in to a kind of women's club. It is inclusive in the 'My bum's a bit like that' sense."

It's also great television. Trinny and Susannah turning Lesley Joseph from Gandalf's mother to stylish fiftysomething in the What Not to Wear celebrity special was a feat worthy of David Blaine. Shifting more hardbacks in a year than Jilly Cooper is little short of miraculous. No one in the fashion industry thought they had it in them.

"Trinny and Tranny", as they were known in the trade, just weren't taken seriously. They should have been. Constantine has an A-list background in designer fashion PR, representing Patrick Cox, John Galliano and Prada. Trinny had worked as a commodities broker and a PR before the two met at one of David Linley's dinner parties then pitched the idea for a realistic fashion column to The Daily Telegraph. Yes, they had relatively charmed beginnings. Both were boarding school gals and Trinny (born Sarah Jane) got her nickname after cutting a pigtail from a hated school chum's head. Ronald Searle, the creator of St Trinian's, was a friend of Trinny's father and remarked, "You're just like a St Trinian's girl."

"It's very easy to pigeonhole Trinny and me and put us in the snotty slot," Constantine has remarked. When the duo started their "Ready to Wear" weekly column in the Telegraph, their fashion hack peers simply thought, "Daddy knows the editor." The column lasted for six years and even their severest critics can't put that down to nepotism. From the early days Trinny and Susannah used salty language in print, referring to "tits" not bosoms and "ass" not bottom.

The column led to a break into television, with TV appearances on This Morning with Richard and Judy. But then came the biggest mistake of their careers. Ready2-shop.com was a case of disastrous timing. The advertising campaign showed Woodall and Constantine from the waist up, naked but for two fried eggs and two melons respectively covering their breasts. The website failed despite the aforementioned £10m venture capital.

What Not to Wear was the duo's first independent network television show. At the start, both women professed themselves nervous that their presenting style might bomb. "We're not sure how people are going to react to us. We are brutally honest," said Constantine. But their delight in exposing their own faults tempers the comments about Jeanette Public having tits down to her ankles and a perm you could go trick or treating in.

For making fashion a popular subject for television they deserve a British Fashion Award. But one has the feeling that Susannah Constantine and Trinny Woodall would decline to accept it. They are too busy developing a clothing range based on the sound principle of hiding women's weak spots to pay any attention to the applause or the scorn of the fashion industry.