The car Samantha Eggar drives at the end of the film is a Maserati Sebring.
Filmed after, but released before, "The Servant" (1963).
Dirk Bogarde and Mylene Demongoet starred together in "The Singer Not the Song" (1961).
The producers talked Dirk Bogarde into playing his Dr Simon Sparrow character one last time after becoming concerned at the lower than expected the box office of the two previous films in the series (in which Bogarde did not appear). At 42 years old Bogarde thought he was getting a bit too long in the tooth to play the naive Dr Sparrow but agreed to play the character one last time after a gentleman's agreement was made giving him a percentage of any box office profits. However the producers supposedly reneged on the deal after the film had been released and a furious Bogarde vowed to never work for them again.