The film's original length was 110 minutes. Bernard Herrmann composed his score for a 110-minute version. However, about 13 minutes were cut right before the film's official release. So some of Herrmann's cues didn't end up in the film. In the released version (97-98 minutes), small portions of Herrmann's cue close to the end of the film were accidentally edited out. Some of Herrmann's cues that he composed for certain scenes in the released version didn't end up in the released cut. One of the unused cues was a cue for the scene where the nurse walks back and enters her car.
The approximately £800 Maura withdraws from the bank would equate to $2,000 at the time or almost $12,000 in 2016.
The St Ives Times and Echo in Cornwall announced on 12 November 1970 that Patricia Neal was scheduled to arrive there the following week to commence location shooting on "The Road Builder." By the time MGM-EMI submitted the film to the British Board of Film Censors on 16 February 1971, the title had changed to The Night Digger (1971). It was passed with an "X" certificate, after cuts.
Though they play mother and daughter in the film, at the time Pamela Brown was only nine years older than Patricia Neal.
In the beginning of the film Patricia Neal's character is shown working as a speech therapist. Later she mentions having had a stroke herself years earlier. In real life Ms. Neal suffered three burst cerebral aneurysms while pregnant in 1965 and was in a coma for three weeks. She survived with the assistance of her husband Roald Dahl and a number of volunteers who developed a grueling style of therapy which fundamentally changed the way that stroke patients were treated. She subsequently relearned to walk and talk and gave birth to a healthy daughter on August 4, 1965.