At the Drop of a Hat was a musical review, described by its authors as "An After-dinner Farrago". The show consisted only of the two artists, Michael Flanders & Donald Swann, sang & played the piano. They initially started at the New Lindsey Theatre (a fringe theatre outside the London West End) on 31st December 1956. The show was successful and transferred to the West End in the Fortune Theatre on 24th January 1957, where it ran for 808 performances. In 1959 they moved to New York City at the Golden Theater.
The two artists performed with only a piano on an otherwise empty stage. Flanders, however, was in his wheelchair because of the result of an attack of Polio during the World War 2. The show consisted of a collection of mainly humorous songs, written by them, connected by topical comments. A second review called "At the Drop of Another Hat" was produced in 1963. Each performance ended with the Hippopotamus Song, in which the audience was encouraged to join-in, followed, in Britain, by a musical rendition of the Lord Chamberlain's requirements.