"I'd not be surprised if there was not a rise in TV licence applications in the locality with such a van parked there for long enough."
Chances are good that the old style TV detector van was a myth, despite the adverts claiming elsewise, and never actually worked/were operated.
It appears, however, that in the age of smart TVs, the idea is making a comeback. Interesting implications; that a private company can consider wifi sniffing and suchlike without reference to GDPR or the DPA, eh?
https://www.theregister.co.uk/2016/08/06/bbc_detector_van_wi_fi_iplayer/
Biting the hand that feeds IT
