Nigel Green died shortly after production from an overdose of sleeping pills; it was ruled an accident but is believed by some to have been a suicide, as Green was said to have been greatly depressed during filming. It had already been decided that his dialog should be replaced by that of another actor in the finished film, Graham Crowden.
Alastair Sim cast himself in the role as the Bishop, according to the commentary on the DVD. He called up his friend Peter O'Toole and told him, out of the blue, of course he'd help him by taking the part. No one was about to turn down the offer of such a great character actor, no matter how eccentric.
The film's writer, Peter Barnes, went to school just outside Bristol, in Stroud. Also just outside of Bristol is a mental hospital, in the village of Barrow Gurney; "Barrow Gurney" has long been associated in local patois with mental illness. Naming the central family in this play "Gurney" seems more than mere coincidence.
In the commentary on the DVD Peter O'Toole says that he did the stunt riding the horse to the hunt himself, because he owned a racehorse, Eric the Red, who'd been a good boy, won a few races and was now retired, and he, O'Toole, had always had this dream that he wanted to ride a real thoroughbred racehorse at a flat-out gallop.
Alastair Sim modeled his characterization of Bishop Lampton on the Primate of All England (chief religious figure in the Church of England), Michael Ramsey (subsequently Baron Ramsay of Canterbury). Portraits of Ramsay in the National Gallery bear a likeness to the physical aspects of Sim's character.