The most famous actor usually does it, particularly if they're in an apparently minor role. This is particularly true in modern ITV detective dramas where they have to be all RADA at the end. You have to be careful, though, you have to go by ITV fame which seems to be its own little bubble: thingy who used to be a vet on Heartbeat would rank way above Al Pacino, for example who, lightwieght B-lister that he is, has never been in Heartbeat, The Bill nor Emmerdale!