Is there no end to the talents of Lily Allen? Not content with her wistfully cute singing career, becoming the new face of Chanel for Karl Lagerfeld and planning to write a musical, she's now turning to fashion. Not just buying clothes - which she does with a vengeance, spending about ?10,000 a year - but as a creative. First, there was her short-lived flirtation with New Look. Now she's announced that she's "helping" Wayne Hemingway to devise his new collection and planning her own label to be sold in her own designer shop.

And Lily isn't the only celebrity getting in on the act. Lindsay Lohan is offering creative direction to Ungaro, Sarah Jessica Parker is "creative directing" for Halston, Cheryl Cole is thinking about launching her own high-street label. Then there are Kate Moss' signature clothes for Topshop, and let's not forget Victoria Beckham, who's come up with her very own collection for women who, amazingly, want to ape her chiselled style.

What all these fashion-come-latelys have in common is that, by their own admission, they have no training in design, no background in understanding the architecture of garments, no known skills in sewing or printing or drawing or cutting. And this can be rather galling for the 40 or so fashion courses flourishing in our universities and art schools.

At the University of Westminster, students learn their craft from the bottom. They have to make a shirt for their first assignment. They have to learn how materials work, to recognise from the texture and quality of the fabrics they use just what may be possible. You want ruching on that collar? Better get stitching. Fancy dabbling with leather bondage? You need to have a thorough understanding of stretch and leeway and how to create understated seams. When does a bias cut cling and flatter and when does it pull and distort? Once a consignment of wool was donated. To our horror, few of the students had been taught to knit so we had to bring in a special teacher before we would let them loose on the yarns.

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By the time they're ready for their final collections, our fashion students, like those in all the finest institutions, will understand how to cut a garment, how a cut relates to the design concept, how to balance feel and sheen and create a finished concept. They will also have an understanding of the history and social meanings of fashion so that, when they choose a particular style or line they'll be able to place it in its cultural context - just like John Galliano has done in his latest collection, which harks back to 18th-century courtesan style, or like Vivienne Westwood, whose newest line is derived from Grimm's Fairy Tales, complete with dashing moustaches - for the women, naturally.

Proper designers, creating beautiful and startling fashions redolent with visual and cultural associations, flowing from or clinging to or redefining the bodies that grace them, are masters of craft. Traditionally, the great fashion pioneers would work as apprentices in one of the haute couture palaces: Christian Dior trained with Robert Piguet; a generation later, Yves Saint Laurent became Dior's assistant. Emanuel Ungaro worked with Balenciaga, Azzedine Alaia with Chanel and Guy Laroche. Giorgio Armani began designing with Cerruti before establishing his own label.

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More recently, designers have learned their trade at art school or at university. That was where Roberto Cavalli developed his revolutionary technique for printing on leather and where Christopher Bailey learned the devices and strategies that propelled him to his current role as creative director of Burberry.

If Lily and Cheryl or Kate and Victoria really consider themselves capable of making stunning, original, desirable and innovative garments, they would do well to consider first the career of the remarkable enfant terrible of fashion Alexander McQueen, who died recently - his empire in tatters but his genius undisputed. Behind the crippling corsets and the live worms he once inserted into a catwalk vest, McQueen was at heart deeply classical. He first trained in traditional menswear in that most Establishment of empires, Savile Row, then continued to refine his passion for fine tailoring as pattern cutter with Romeo Gigli. And then, probably after completing the 10,000 hours of application that Richard Sennett, in The Craftsman, insists is the basic requirement for any skill, he took a postgraduate course at Central St Martins College of Art and Design.

And it was partly this careful training and expanded education that produced this combination of brilliant technical skills and an uncanny ability to infiltrate into his own startling designs a counterpoint of older styles and associations: flamboyant use of tartan in reference to the historic oppression of the Scots; his marine collection, which included references to the Biblical flood but was more directly inspired by Charles Darwin's On the Origin of Species.

Kate Moss is a stylish woman with a sharp eye for current trends and combinations. Sarah Jessica Parker is a brave exponent of edgy fashions and happy, at least in her Sex and the City persona, to make public mistakes. Lily Allen, meanwhile, is a bright young woman with a lust for fame. All have talents; all these celebrity "stylists" look great in lovely clothes. But Alexander McQueen they are not.

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Their absurd aspirations remind me of the Jewish arriviste who, in order to announce his acceptance into the higher echelons of society, purchases a boat and a jaunty naval cap to wear at the wheel. "Now I'm captain of my own ship," he declares proudly. His father, the tailor, tuts and shakes his head wisely. "By you, you may be a captain," he warns. "By me, you're a captain. But by a captain - you're no captain."