Knickers. They're everywhere. And if that sounds like the most almighty case of stating the obvious, the fact that any underwear is currently being worn over clothes rather than hidden away beneath them or, failing that, that the clothes in question are so sheer that knickers show through is perhaps less commonplace.

Or is it? Any fashion insider will know that visible underwear is a catwalk folly that only rarely has much bearing on reality. Big knickers may be worn beneath lace or chiffon on the runway and set the flashbulbs popping, although this look is unlikely to impress workplace colleagues in a good way. Big knickers may also be worn beneath just a coat because, in truth, the collection wasn't that great to begin with and said coat looks better without anything as disruptive as, say, any actual clothes to dilute its impact. Finally, big knickers are a way of sexualising a wardrobe and the woman who wears it. Sex sells, or at least the image of it does. Witness the success of Jean-Paul Gaultier and Dolce & Gabbana.

Like any catwalk stalwart, visible underwear means different things to different designers. Take Betty Jackson's variation on the theme. The designer should be applauded (or blamed?) for the fact that, in her current collection, and a good six months before everyone else set the big knicker onslaught in motion, she sent a pair down her catwalk printed with the face of Henry VIII on the front and Anne Boleyn from behind. They currently take pride of place in the window of her Knightsbridge store and are selling like hot cakes. This approach is humorous, clearly. There's nothing quite like a pair of right royal underpants to brighten up even the darkest of days.

Après Betty, le déluge. At the Paris collections this week, Christian Dior featured the type of foundation garment most readily associated with 1950s starlets under gossamer evening dresses. Over the waistband of Junya Watanabe's denim pieces peeped a leopard-print thong. This is about as close to pandering to celebrity culture as this designer is ever likely to come. At Martin Margiela, knickers were worn under American tan tights. What, no skirt? Most bizarrely of all, on Gaultier's catwalk, knickers were worn over wide-legged tailored trousers. Best, dear reader, not to try this at home.