Re: I'd still like to know...
The vans are all smoke and mirrors. Whilst it could be possible to detect the signals generated by CRT TV's back in the day, flat panels are a whole different ball game, plus a 1920x1080 monitor would generate signals just like a 1080P TV.
The "detector" van works from a database.
Property used to have licence, didn't renew it = Knock on door.
Property just bought a new TV and don't have a licence (you did know that retailers take your address to log the sale of a TV didn't you?) = Knock on door.
To a lesser extent Antenna on roof and no licence = Knock on door.
I'm sure they make a continual pain of themselves round any new development as the new addresses appear on the database.
Whether the snoopers charter will extend to allow the BBC to demand names and addresses of people accessing their streams is something I'm sure we'll find out very soon.