This British movie was much more popular in Italy than in Britain. Executive Producer, Writer, and Director Sidney Gilliat expressed admiration for the Italian title - which translates as "Champagne After the Funeral" - and wished he had thought of it for a British title.
The lyrics that Hayley Mills sings are from William Blake's "Auguries of Innocence" (circa 1803): "Every night and every morn Some to misery are born. Every morn and every night Some are born to sweet delight. Some are born to sweet delight, Some are born to endless night." (Jim Morrison lifted some of Blake's words from the same poem for The Doors' song "End Of The Night".)
Agatha Christie, author of the source novel, was reportedly unhappy about the inclusion of a sex scene with nudity in the film.
Gipsy's Acre scenes were shot on the Isle of Wight. There's no house there, but to see the view that Michael loves the coordinates are 50°39'36.43"N 1°25'25.61"W; a 10-minute walk west from Jubilee car park at the junction of Strawberry Lane and Lynch Lane.
The singing voice of Hayley Mills was dubbed by opera singer Caroline Gilliat in the movie, daughter of the film's director.