During the filming, Charles Hawtrey's mother would often visit the set. Whilst enjoying a cigarette, she accidentally dropped lit ash from the cigarette into her handbag. Joan Sims who was the first to spot the incident yelled, "Charlie Charlie, your mother's bag is on fire!". Charles Hawtrey poured his cup of tea into the bag, snapped it shut, and carried on.
The "children" in the movie are meant to be the equivalent of 6-8 graders, but actually they are played by young adults. This was no mistake - the producers wanted to avoid having to ask the childrens' mothers for a fee for their appearance as required under Britain's child labour laws.
Ted Ray was under contract to Associated British (ABC), but wasn't used by them. So they weren't happy when he turned up in another distributor's film, especially one as successful as this one. Due to the possibility of the film not getting a release on the ABC cinema circuit, Ray was quietly dropped from the Carry Ons. He was supposed to be in the next one, Carry on, Constable (1960).