Liz Fraser (Ethel) was still learning to drive at the time the film was made. In the scene where Ethel follows the army convoy in an Aston Martin, she kept stalling as she set off on cue, so ropes were attached to the front of the car, out of shot, and it was towed.
Peter Sellers proved very difficult for director Robert Day to work with and, at one point, even walked off the film. He was eventually persuaded to return, but Day later calculated that he had put about ten days on the shooting schedule through his tantrums.
Maurice Denham plays the Governor who has his watch stolen. In the TV series Porridge (1974), he plays a jailed judge who has his watch stolen.
Characters named "Jelly" (Knight) and "Lenny", also depicted as members of the central character's criminal gang, turn up in Rotten to the Core (1965), another British comedy co-scripted by John Warren and Len Heath. However, they are played by different actors.