Is a Jaffa Cake a cake or a biscuit? A tough question for Matthew Sweet and the drinkers at The Philosopher's Arms, a pub offering both beer and philosophy. Among those helping him resolve this important conundrum are a Cambridge professor of philosophy and a former winner of the Great British Bake Off, who will be turning up in the pub with a very large, and possibly quite tasty, Jaffa Cake. Producer: David Edmonds.