Wi-Fi Intercepts
The difficulties that wi-fi detector vans will have is quite considerable as in a city there will be wi-fi sources everywhere. Tower blocks will of course be another problem. As to the data-packets, how will they be able to tell the difference between YouTube video and BBC video data packets? Presumably they would need to crack the wi-fi password to do that? The vans will of course be "frighteners" intended to make the gullible cough-up.
Decades ago in the days of CRT televisions, detection was easier as the wood and plastic TV cabinets gave no screening whatsoever against electromagnetic radiation. One chap that I heard about didn't like this so he took his telly to bits and lined the cabinet with two layers of very fine chicken wire. The chicken-wire is also superb for supressing ignition noise on fibreglass cars (Leyland Minis with fibreglass fronts used to be very naughty with severe radio interference until doctored)
There needs to be another way to finance public service broadcasting as the present method is worse than the Poll Tax.