You can be sure that if "they" wanted to pursue "non-licence payers" these days, the work would be farmed out to Serco, Capitas, G4S (or some other such quasi-governmental "agency" of dubious competence).
As I may have mentioned before, I have not owned a TV set for many years (over 23 now, at least), and so have some experience of threatening letters, and all the rest.
Although Urban Legend (myths?) would have it that "snoops" are indeed about, it makes you wonder how they actually go about it. Listening at the door, perhaps?
Maybe they have someone rummaging through wheelie bins for discarded copies of the TV Times
(or whatever it's known as these days). Who knows?
"Looking for TV aerials" is another I have heard about. But how can that
be any good in blocks of flats, or indeed "dwellings in multiple occupancy"?
I'm pretty sure that the whole thing is just another example of frightening folk into coughing up the "Licence" fee. In other words:- scaremongering. Not that we would know anything about that
forum, of course.