Although crotch length is de rigueur on MTV, for most of us, hems have pretty much maintained a presence around the knees since the mid-Nineties. Quite why this length inspires such constancy may prove fruitful ground for future psychologists. My own theory is that it just works, especially if you don’t like your knees.

Hems have long been a fascinating topic of research for financial analysts with too much time on their hands. Ralph Rotnam, a stock analyst for Harris Upham in the US (quelle surprise) was the first of this breed to come up with a cunning wheeze for spending lots of time looking at pretty girls’ legs, sending out a newsletter to clients in May 1967 with the immortal words: “For some time there has been a suspicion in Wall Street that the stock market and the hemlines of women’s skirts move in the same direction. To find out if this was true, we sent our textile and apparel researcher, Foy Roberson, to the library to make a detailed study.”

The library? Oh well, I dare say there was even more unstinting dedication to this detailed study once Foy returned to the offices of Harris Upham with the findings. And so the correlation between frock lengths and shares (short equals bull market, long equals bear) was forged, providing endless happy hours of speculation for all concerned.

The thing is, as we know, fashion is cyclical, like markets, seasons, J-Lo’s marriages, Jordan’s implants and the hissy fits on The X Factor. Pinpointing a moment in each and basing an everlasting theory of economics on it strikes me as dodgy financial science. If you really want indicators of the rise in global wealth, you’d be better off examining the average gargantuan designer handbag or the freakish heights of fashionable heels, which, in future years, will surely be viewed with the same curiosity we now reserve for the powdered wigs of the late-18th century.

But what do I know? Because guess what, bang on cue, longer lengths are back. The catwalks proposed them last winter, with a morbid succession of dreary calf-length skirts. I’m proud to report that women, one and all, resisted. Bloodied but unbowed, designers then unleashed the maxi. Having flopped last summer, it’s kicking in 2008. WAGs especially have taken them to their hearts,­ which is why I remain sceptical about the Ralph Rotnam theory. These girls wouldn’t know a recession if it came with monograms and a waiting list.

But hark, what noise yonder? Why, it’s the gentle flip-flopping of a million pairs of pancake-flat sandals, gladiators and Fit-Flops. Flat happens to be what goes best with a maxi, the combination of wedges and all that fabric being too bulky and fussy. Bags are shrinking, too. So how worried should the FTSE be? Time for Foy to visit the library again.

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