Benjamin Britten had written some music for the Crown Film Unit in the past and wrote his guide to the orchestra for them as well. The film was called The Instruments of the Orchestra, and it carried the subtitle "Variations and Fugue on a Theme of Henry Purcell." The theme comes from incidental music Purcell had written for the play Abdelazar, by Aphra Behn.

Britten introduces a fully orchestrated version of Purcell's theme, and then proceeds with variations on this theme featuring different families of instruments..The final fugue re-introduces the instruments in the order they appeared. The piece ends almost exactly as it begins, but this time with a more learned audience.