The story goes that Eleanor Bron and John Cleese were filming at the same studio as the Doctor Who folks. Douglas Adams persuaded them to film a brief art critic scene, originally intended for "Two Englishmen." Having had attained popularity through Monty Python, Cleese agreed to do it only if there would be absolutely no pre-publicity running up to the film's release. He didn't even want to be credited with his real name. Doctor Who's famous guest stars can be pretty picky.