within 21 days, some clients were being offered anything up to three years to pay.

And now, one collector told the Evening Standard that he was phoned up and offered a work that had already been sold at the auction, which suggests - though Sotheby's deny this categorically - that buyers are getting cold feet and reneging on deals. Over the summer, a gallerist tells me, auction houses were so inundated by collectors selling minor Hirsts that they've had to start refusing them. "Dealers are offering larger and larger discounts, though they never admit to this even in the high times", he said.

The Johnny-come-latelies have assets worth nothing near what they paid

Just like the housing market boom, it's the Johnny-come-latelies who are now sitting on assets that won't fetch anything near what they paid for them. Some of these are people, one seasoned sale-room hand put it, "who think Piero della Francesca is a shoe shop".

It isn't hard to see how they ended up paying over the odds for a later spot painting or a collage of dead butterflies. As the last crash was as long ago as 1991, speculators must have thought that prices would go on rising forever. Darlene Lutz, Madonna's long-time art advisor, told the New York Magazine: "This market is fuelled by collectors who have never been through a correction... the generations who did are watching this with disbelief. It's like teenagers who have unprotected sex thinking they'll never get pregnant. And then, whoops - look what happened!"