Humphrey Carpenter suggests Spring 1920 is the most likely date of composition: Britten's Aunt Florence, headmistress of a girls' school in Barbados, met the Prince of Wales during a Royal visit to the island in March 1920. See Carpenter, Benjamin Britten (London: Faber and Faber, 1991), p.7.
This musical 'work' is simply a short extract included in Britten's play of the same name.