There have been a few attempts at transporting Discworld to the screen, from Cosgrove Hall’s animated adaptations of Soul Music and Wyrd Sisters, to the more recent Sky productions of Hogfather, The Colour of Magic and Going Postal. But beyond the brief glimpses we get of such characters as Angua, Nobby Nobbs and Visit-The-Infidel-With-Explanatory-Pamphlets, the Watch novels have yet to reach our television sets. Why?