The Singing Cop is a 1938 British musical comedy spy drama, directed by Arthur B.
The film was a quota quickie production, based on a short story by Kenneth Leslie-Smith.
[1] A temperamental opera diva arouses official suspicion that she is a spy, secretly gathering classified information to pass to enemy agents.
A policeman who happens to be a talented amateur singer is sent undercover to join the opera company and try to find out whether there is any substance to the allegations.
The policeman lets his lady friend into his confidence, and the pair set about sleuthing.