Currently the police can add anyone to the ANPR database for the flimsiest of reasons. For example, people have been ANPR marked for simply attending a peaceful demonstration; or even for parking near one.
The police take an ANPR entry as reason to stop and search, to invade privacy, etc.. Someone who is marked is going to get repeated contact with policemen who (naturally or not) assume that you must be guilty of something. This is beyond policing: it's punishment without a trial.
There is no way to know if you have an APNR mark. There is no way to appeal.
And this is just the tip of the mass surveillance iceberg. We could talk about the activity of the police "Forward Intelligence Teams", also.