Veteran actor James Donald was coaxed out of retirement to play the doctor. It was Donald's penultimate movie, with his final being Le grand sommeil (1978).
This movie was voted as one of the Top Ten Films of the Year by the U.S.'s National Board of Review in 1975.
Jeremy Clyde of the singing group Chad and Jeremy had played the lead in the play in London. He wasn't considered for this movie, however, as the studio wanted to go with a more established star.
This movie was released six years after its source stage play of the same name by Barry England had been first performed during May 1969, at the Theatre Royal in Bristol, England.