Armstrong appeared in BBC Radio 4's "The Very World of Milton Jones", broadcast between 1998 and 2001. He narrated the animated cartoon series "The Big Knights" in 1999; it first appeared on BBC1 that Christmas. That same year he also starred as Prince Charming in ITV's Christmas pantomime, alongside Ben Miller, Samantha Janus, Paul Merton, Harry Hill, Frank Skinner and Ronnie Corbett. Between early 2000 and early 2001 Armstrong starred as a misanthropic, animal-hating vet in the BBC One sitcom "Beast", and he has also been the star of a series of TV commercials for Pimm's.