Spend enough time in the world of commerce and an ineluctable truth emerges: everyone talks their own book. Stockbrokers push shares, estate agents are bullish about property, entrepreneurs puff their companies and art dealers hype art.

But just as the other asset classes have caved in during the past year, so the value of art must crash. And no part of the art market is more vulnerable than contemporary art, which has risen so very high on little more than PR and salesmanship.