Derby Day is a 1932 three-act light opera, with music composed by Alfred Reynolds to a libretto by A. P. Herbert. Herbert wrote his text between March and May 1931, whilst on a trip to Australia, during the first run of his successful Tantivy Towers. One contemporary review described the work as "mainly a Cockney opera", and praised the work as "topical in the best sense" and said of the music: I do not know if Mr. Reynolds is himself a Cockney, but I do know that his Cockney music, particularly in the coster scenes, is the best that has ever been written.