I've been in one and played with the equipment. They do (or did) exist and do work.
These days though, it is more likely to involve a hand-held device, since they already have the addresses of people without licences and just walk up to their front door.
My evidence ===== The Communications (Television Licensing) Regulations 2004 includes Definitions for the purposes of the Communications Act 2003 and the Wireless Telegraphy Act 1967
Meaning of "television receiver" 9. - (1) In Part 4 of the Act (licensing of TV reception), "television receiver" means any apparatus installed or used for the purpose of receiving (whether by means of wireless telegraphy or otherwise) any television programme service, whether or not it is installed or used for any other purpose. ====== If it is not installed or used "for the purpose of receiving ... television programme service" it doesn't need a licence.
You may have reference to an older Regulation or Act, but this is the current law.
In the early days of 'TV Detection Vans' my uncle worked for the GPO/BT.
At the weekend he would earn overtime by driving the van around likely estates. The idea was to look conspicious with the van clearly identified with large letters. No detection was actually done but it got people scurrying down to the P.Office on the Monday.
One of my customers used to be a TV licence inspector. Seeing a working TV through the window and then knocking on the door was his number one way of catching out the nonpaying users. Calling when Corrie or Eastenders was on was a cert. During an England football match was also a good time to call.
Of course he always started by saying "You do not have to say anything etc" which usually scared the homeowner into admitting everything.
The only technical bit of TV licencing enforcement is the electronic database.
"well yer honor, I installed me 54" plasmaa and surround sound , and satellite dish and Digital aerial just to impress the neighbours, no we never watch it."
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