Peter Sellers won great acclaim for his performance in this movie, but was difficult to work with throughout the filming. He repeatedly asked Director Sidney Gilliat to replace Virginia Maskell, who played his wife, and, when Gilliat refused, he became convinced that this movie would be a disaster, said so publicly, and sold his percentage of the profits back to Launder and Gilliat. It proved to be a big commercial and critical hit (with Maskell winning excellent reviews), and so he lost out on a lot of money. Perhaps because of this, he continued to bad-mouth the movie for the rest of his life.
The sequence in which John Lewis (Peter Sellers) reviews a local drama production without seeing it, unaware that a fire at the theatre has caused the performance to be abandoned, was inspired by a real-life incident in the journalistic career of Dylan Thomas.
Richard Attenborough (Gareth L. Probert) and Gerald Sim (Cigarette Thief at Party) were brothers-in-law in real life. Attenborough was married to Sim's elder sister Sheila Sim from 1945 until his death in 2014.
Author Kingsley Amis lectured at Swansea University for several years, and the fictional Welsh town of "Aberdarcy" in his novel and this movie is a portrait of Swansea, which was the movie's primary location.
Presumably due to the depiction in this movie, Swansea Library would not give permission for filming. This movie used the Glynn Vivian art gallery, directly over the road, for exteriors instead.