If I really wanted to spin out this credit crunch thing, I could tell you that, with incredible prescience and tremendous altruism, designers have decided to spare our wallets this season by peddling a load of old ideas that we've seen and bought a million times previously.

That argument would obviously be tedious beyond the call of duty. Anyway, I doubt that altruism had much to do with it. Still, the fact remains that in this season of mists (or, in modern meteorological parlance, thunderous downpours interspersed with flash-flooding) and backto-school anticipation, when one positively glows at the prospect of all things new, there are an awful lot of familiar ideas around.

To recap the story so far: drainpipes are back (although, to my certain knowledge, they never went away). Ditto ballet pumps, platforms, pencil skirts and puff skirts. I won't lump peg-leg trousers in with the déjà vu just yet, despite qualifying on alliterative credentials alone, because while they were also around last season, it was in such small numbers as to count as an early adopters' trend, and therefore eligible for a second go.

I don't have a problem with the familiar. It's unsettling - and expensive - when fashion experiences one of its periodic volte-face. Anything that encourages us to take stock of what we have and devise clever ways to refresh it with one or two well-chosen new additions sits fantastically well with what passes for my consumer conscience. But when does a love of what you know become a form of stasis? Where does retro slip into nostalgia?

The Eighties are still being endlessly trawled through by designers and stylists desperately panning for gold and heroically refusing to accept the blindingly obvious: there wasn't any. So what's that all about? The Thirties, Fifties and Sixties are also in the top five of recycled eras. Exquisitely styled - and self-referential - TV series and films such as Mad Men (Eisenhower Sixties), The Edge of Love (Forties London and Wales, but with much, much better hair), Brideshead Revisited (stinking reviews, but blameless bias-cutting) and The Duchess (brace yourself for a calamity of corsets and pastel bustiers) keep the flame for period fashion burning brightly - more brightly, probably, than it did first time around, historical figures being notoriously grubby.

Generally, trends get better with repeated airings. The eye has already adapted, any awkwardness is smoothed away. By the fifth repeddling, even horrors can look quite refined. After all, Hollywood succeeded in making fictional white-powdered hair a fact of 18thcentury aesthetics, when in reality the powder turned hair a rather dingy grey. And The Tudors, BBC Two's enjoyable claptrap, has managed to make Anne Boleyn look like a kind of Catherine Zeta-Jones wannabe. Who knew they had facelifts and La Perla in 1533? At this rate Lost in Austen, the Life on Mars meets Mr Darcy ITV1 offering that starts tonight, will end up making mobcaps fashionable.

That still doesn't explain why designers - supposedly agents of the new and the shocking - love revisiting scenes of past glories (and crimes) so much. Or perhaps it does. Studying a stilettoed mule intently in Paris in July (this is the kind of thing that fashion editors do), I listened while Alber Elbaz of Lanvin, one of fashion's more thoughtful designers, explained why something that looked so wrong five minutes ago can suddenly look right. It's timing, stupid. Or to paraphrase Stefano Pilati, of YSL, being too early can be as bad as being too late.

The modern designer has to be a sophisticated horologist. There are multiple lessons for the consumer here, too - wearing the right thing at the right time, revisiting the props of happy memories, reinventing personal hits so that they flatter us as we are now, rather than as we were...

In the meantime, designer houses continue to vacuum up the contents of vintage stores as well as buying up archives of old Vogues and Harper's Bazaars - to the point, Elbaz says, where some decades have been bled dry. “But that won't stop the lure of retro,” he adds. “The challenge to reinterpret is as strong as ever, especially when so much has already been done. Besides,” he notes with disarming candour, “with all the collections and pre-collections we design now, there's not enough time each season to sit down and design something that came out of nowhere.”

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