That Time Douglas Adams got Monty Python on Doctor Who
It Goes Ding When There's Stuff
Well, maybe he didn’t get all of Monty Python on the show, but he did get John Cleese. City of Death was written by David Fisher, but heavily re-written by none other than then-script-editor Douglas Adams. When Adams learned that John Cleese would be filming in the same studio on the same day, he persuaded the actor to come in and cameo as a speaking part written for generic art gallery goers. Cleese agreed, on the requirement that his appearance on the show not be announced or publicized in any way, leaving it a bizarre non-sequitur that any Python fan would appreciate.
(via The Geek Twins.)