We expect certain artists to sell for millions at auction, but would we ever have thought that a vandal would become one of the biggest names in contemporary art? The pseudonymous artist known as Banksy has disrupted the art market yet again, with the recent sale at Sotheby’s of the painting Devolved Parliament (which depicts MPs as chimps in the House of Commons) for £9.9 million, five times its estimate. It was a world record...