Michael Crawford performed all his own stunts. When performing stunts, he usually wore gloves, so if he suddenly appears wearing them, a stunt is usually about to follow. For this reason, there sometimes appear to be continuity errors (no gloves/gloves/no gloves).
The rhythm of the theme tune is based on the words "Some Mothers Do 'Ave 'Em" (minus the apostrophes) written in Morse Code.
When filming the show, Michael Crawford had to perform scenes over and over in front of the extras and other actors, until they no longer seemed funny to the cast and crew. Even then, some takes were still ruined by someone giggling in the background at Frank's antics.
The final series was written by Raymond Allen based on stories suggested by Michael Crawford (not written by Crawford himself as sometimes reported).
Elisabeth Sladen was interviewed by producer Michael Mills for the role of Betty but lost out to Michele Dotrice. However, Mills offered her a guest role in the series as Judy in The Hospital Visit (1973). Linda Hayden was also considered for Betty.