I watch very little telly (and I've not seen the programme you're referring to because 'Passport to Pimlico' was on Gold at the time anyway) but I'm often astounded by the basic errors shown in police dramas.
For example, I was at friend's house when a soap (Eastenders?) was on the box. The police took the suspect to the police station, immediately charged him and then started interviewing him. The provisions of the Police and Criminal Evidence Act were completely ignored.
Similarly, dramas like 'Frost' and 'Lewis' frequently feature the lead characters asking a suspect loads of questions in their own homes (or, for example, at their places of work), without first cautioning them, without any other officers being present as witnesses to the questioning but often with other people (who might later base their own stories upon what they've heard the suspect say) in the room.
I was once travelling back from Paris on Eurostar, while the passenger seated next to me was reading through a script and making notes in it. I couldn't resist reading it out of the corner of my eye and I found myself struggling to burst out laughing at the preposterous actions of the police characters in it. I assumed that the script was simply the self-penned ramblings of a novice writer until he turned back to the front cover, where I saw the title of the production together with the name of the director, which matched the name on his rail ticket. Yes, he was the director of 'The Bill'!