All the British cast speak French instead of being dubbed, as it was the common practice at the time.
This was Valerie Hobson's final role before her retirement from acting, which took place shortly after her marriage to the British Conservative MP John Profumo.
French actor Gérard Philipe does not speak a single word of English in the film.
Some of the footage showing London the way it really was in the early 50s, not gussied up for filmmaking, was captured with a hidden camera.