Catherine Tate and David Tennant were partners in travels (I almost wrote “partners in crime” 😀 ) for about one year (one season and one Christmas special episode) on Doctor Who sets. More, they played together on a theater stage.
Also, David Tennant played a small part in Harry Potter series and now (in the video) Catherine Tate is trying to guess his character. From ‘The Justin Lee Collins Show’. Enjoy! 🙂