Under Your Hat is a 1940 British musical comedy spy film directed by Maurice Elvey and starring Jack Hulbert, Cicely Courtneidge and Austin Trevor.

Suspicious that Jack may be embarking on an affair with his glamorous co-star Carole Markoff, Kay follows him to the South of France, where in fact he is due to receive the carburettor from a contact at a night club, as he has actually been recruited as an undercover man for the government.

[3] It was based on a popular stage musical starring Hulbert and Courtneidge, a husband-and-wife team who had made a series of successful comedy films during the 1930s.

"[6] Kine Weekly wrote: "Scintillating musical comedy espionage burlesque, competently and ambitiously adapted from the persistent West End stage suvvess. ...

"[5] Sky Movies wrote, "although Jack Hulbert and Cicely Courtneidge had passed their mid-Thirties' peaks as box-office attractions when they made this film version of one of their hit stage shows, it does mark something of a return to form for both of them, with a lively if improbable plot involving spies, and the two stars cheerfully indulging their penchant for disguise.