This movie never explains its title, which refers to a traditional children's rhyme: "Peter, Peter, pumpkin eater/Had a wife, but couldn't keep her/So he put her in a shell/And there he kept her very well." This serves as the epigraph of Penelope Mortimer's original novel.
Patricia Neal was offered the lead, but when it was not 100% confirmed that she would get the role, she opted--to her later regret--to make Psyche 59 (1964) instead, since it was an official offer.
This was considered a very prestigious British film when it was made. It had a large budget and took 16 weeks to film, although it is under two hours in length. Some very famous actors--James Mason, Maggie Smith, Richard Johnson, Sir Cedric Hardwicke--were hired to play what were actually very small roles occupying only a few minutes of screen time. However, it was a box-office failure and reviews were largely disappointing. When it was first shown on British television in 1971, it was cut by 12 minutes, occasioning an angry letter to the press from screenwriter Harold Pinter. Asked in later years to account for why the film flopped, James Mason was inclined to blame Pinter's script, which was rather more vigorously attacked by Penelope Mortimer, the writer of the original novel. The film's failure had a bad effect on the career of director Jack Clayton, who subsequently made only four more films and one television movie, although he lived for over 30 years more.
The Cobstone Windmill country-home location was also used in Chitty Chitty Bang Bang (1968), Went the Day Well? (1942), and Night Creatures (1962) among other films. At one time, beginning in 1971, the property was owned by Hayley Mills and her husband at the time Roy Boulting.