I think that with regards to scanners, a bit of common sense is normally applied.
The cost for the enforcement agencies, to prosecute even the minor offenders is beyond proportion inrelation to the severity of the offence, because in order to gather evidence of a person "listening" to a frequency you would need to do covert surveillance requiring an authority in line with the Regulation of Investigatory Powers Act.
The whole thing moves up a notch when either an unauthorised person acts on that information or actually transmits on that channel. This is quite a severe offence and is usually one which is frequently targetted by the various agencies.
Thepirateking hit the nail on the head. My analogy is that the vast majority of drivers speed, but not all speeders are dangerous drivers. The limited resources available to enforcement agencies mean that whilst there are a lot of offenders, it makes more sense to target those who speed dangerously or in dangerous locations.
Mazzy, BTW great thread and I'm on the edge of my seat waiting your first solo.
Regards
Obs cop