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.
How old is he now, my love?
Fred's wife: Eight months, dearest.
Fred: But I've been in here nearly two years.
Fred's wife: Oh yes, Fred. But you sent me some *lovely* letters.
When Crout inspects the three prisoners' cell, Lane squirts an air freshener to clear the smell of cigarettes, then thrusts the freshener into his jacket pocket. For obvious reasons, prison jackets are never equipped with pockets.
Opening credits prologue: H.M. PRISON HUNTLEIGH