A French Mistress

A French Mistress is a 1960 British comedy film directed by Roy Boulting and starring Cecil Parker, James Robertson Justice, Agnès Laurent, Ian Bannen, Raymond Huntley, Irene Handl and Thorley Walters.
It is based on a stage play, "The French Mistress" by Sonnie Hale under the pen name Robert Monro, first produced in 1955 at the Theatre Royal Windsor, 
starring Hale.
Plot summary.
A young French woman, Madaleine Lafarge, is unintentionally appointed as the French teacher at an English public school for boys, which is not used to having women teachers. She causes a stir with pupils and other school staff, and complications ensue.
A romance develops between Lafarge and the headmaster's son who is also a teacher at the school. This is a cause of concern for the headmaster when he comes to believe that she is his daughter, from an affair he had during a holiday in France in his youth. He attempts to stop the romance by sacking her, so that she will go back to France, but the boys go on strike and nearly riot. All the problems are resolved when it becomes apparent that she cannot be his daughter.
Critical reception.
Bosley Crowther in The New York Times wrote, "We would have expected something better from the Boultings and Mr. Dell. A good cast of old familiars—excepting Agnes Laurent, a newcomer who plays the mademoiselle — try to do something with it and occasionally do all right with a line here, a facial expression or a situation there. Cecil Parker puffs and pouts as the headmaster, and Ian Bannen stands up stoutly as his son. Raymond Huntley and James Robertson Justice do their acts as other masters in the school. Irene Handl also draws a few fast laughs as the compulsively pugnacious cook, and Edith Sharpe and Athene Seyler cluck politely as the only other females around the place. But the ministrations of the stalwarts do not quite save the day. The Boultings are onto a sticky wicket with that silly sex-scandal stuff." 