Those vans were a myth. They were based on the radio signals that Cathode Ray Tubes produced. In theory, with the right receiver, you could pick up the signal from a TV set if it was switched on.
They never had any "detector vans". And CRT sets haven't been made since the 90s.
TV Licencing is a brand name of Capita Business Services. They are a PRIVATE firm, which take on a lot of Government and LA admin contracts.
Their "enforcement" methods consist of using a database which lists all addresses with a current licence, so by deduction, any address not listed is likely to be unlicensed.
The "inspectors" are just sales people, they have absolutely no statutory authority what so ever. They get £20 commission for every licence they sell and £50 for each successful prosecution. This tops up their basic salary.
You do not have to talk to them, they have no powers or authority. They are literally just private citizens who go around knocking on doors and asking people questions.
They are mostly unemoyable in any other job, are about the lowest form of predatory scumbags, and are not the type of people you should lower yourself by talking to.