Shoota, "Once a cop.." but not Dixon of Dock Green. He was fictional and lived in a fictional world that never existed, but which fitted the nostalgic fantasies of the older generation.
Mind how you go. (A statement steeped in hidden meaning, if ever there was)
Another favourite is "Why do you think we stopped you , sir?". This invites an admission of some wrongdoing. The correct answer is almost as bad viz,. "If you don't have any idea , officer, I really can't be expected to guess and supply one, however misguided. And I am not a mind reader, you know"