On 15 September Damien Hirst has a surprise in store for the art world and perhaps also for himself. At the New Bond Street Sotheby's he will mount an audacious two-day auction, entitled Beautiful Inside My Head Forever, of 223 artworks, made by himself and to be sold by himself. This is a money-spinning feat by a living artist on a scale never attempted by an auction house or an art gallery. For this reason alone there are mutters along Bond Street that Hirst's sale will be the moment that his bubble bursts.