The world's most expensive fag butt? Signed and numbered by Damien Hirst and embedded in Perspex, London auctioneer Bonhams estimates it will fetch pounds 200 to pounds 300 when it goes under the hammer in the launch sale of Bonhams' new "Futures" department on 15 May at 2pm.

Hirst gave away 25 cigarette butts to readers of The Idler, a sort of Spectator for the young and addled, to commemorate a night's boozing with its editor, Tom Hodgkinson. The Idler's first pint had drawn from Hirst the admission that he had employed others to put the spots on his famous spot paintings. The fag butts are no more original. The morning after, he sent 25 signed, numbered - but unsmoked - Marboro Lights and Silk Cut cigarettes by courier to The Idler's London offices. The staff formed a ritual circle and smoked them.

The really artistic bit came when art director Gavin Pretor-Pinney chose a refrigerator ice tray as a mould for the molten perspex. The resulting artworks - inanimate objects suspended in a medium - could hardly be more Hirst-like.

The expected pounds 200 to pounds 300, Bonhams admits, is a guesstimate. Only four Hirsts have come to auction so far. At Christie's in October, a Hirst spot painting made pounds 36,700, and in the same sale his ping-pong ball and glass, with printed instructions about how to float the ball in the glass, made pounds 862.50. Now, why can't he stick to really useful things like that? John Windsor