The same prison infirmary set was used for the Blackadder goes Forth episode 'General Hospital'.
The script allowed the prisoners to swear without offending viewers by using the word "naff" in place of ruder words ("Naff off!", "Darn your own naffing socks", "Doing next to naff all"), thereby popularizing a word that had been recorded at least as early as 1966. Ronnie Barker did not claim to have invented it. In a television interview in 2003 it was explained to him on camera what the word meant, as he said he hadn't a clue. The word was actually a piece of slang for heterosexual men which was popular among homosexual men. It was an acronym for "Not Available For F******".
All who knew Richard Beckinsale were shocked and devastated by his death, particularly Ronnie Barker. He was so upset, he couldn't work for several days.
The judge reading sentencing during the opening titles is voiced by Ronnie Barker. Barker is reported to have said that he regretted recording himself as the judge (who was later portrayed by Maurice Denham in two episodes).
The character of "Harry Grout" played by Peter Vaughn, became one of the show's most memorable and celebrated creations, despite only featuring in just two episodes and one Christmas special. He would become a more significant and central character in the 1979 film version.