Also not a lawyer, but I believe similar to other criminal cases, the investigator, then the prosecutor, then the judge and/or jury would need to make subjective judgement calls to decide whether or not to move ahead with prosecution, based on the specific situation.
For example a TV with built-in tuner and no other equipment (no DVD player, no console, etc etc) they would likely be able to argue that you do watch live TV even if you weren't witnessed doing it, whereas a TV that isn't connected to any aerial but is connected to an Xbox you could probably convince them otherwise without even leaving your own home.
I suspect that they would also lean towards giving the benefit of the doubt, because it's such a minor crime that if there's a chance you'd be found innocent in court, or that they'd have to spend time investigating further, it's a much better use of their time to move on to the next person.
But I could well be wrong.