He was sent to Los Angeles by the BBC in the early 1970s to interview
Groucho Marx for television - an occasion so disastrous that he later wrote about it at length, and often recalled it in interviews. Groucho proved extremely fractious, was sour and unfriendly throughout, used a great deal of coarse language, was utterly unwilling to be affectionate about anyone and told a great many tasteless and slanderous stories about beloved film stars. A large part of the several hours of interview footage was deemed by BBC lawyers to be actionable in law, and most of what remained was too unpleasant to be screened. At the end of the interview session, Muir and Groucho found a common bond in their fondness for Gilbert and Sullivan and sang a few duets together. When the show was finally shown, it was noticeable that there was relatively little conversation, an awful lot of extracts from Marx Brothers movies, and rather more Gilbert and Sullivan than anyone might have expected.