Apparently they have a few different technologies in the van - one is to detect the flyback in the CRT. I think this is mainly just additional to the IF detectors.

It has long been known that 9/10 detector vans are fake - I read a report a few years back thay quoted somebody who was involved in painting the wooden aerials silver! Somebody also inspected a van at a display outside a railway station - there was a nice 60cm Sky dish on its roof and bench seats in the back behind the tinted glass!

These days it's much easier for them to cross reference the database of licensees against the Royal Mail database and mailshot anybody who hasn't got a license. Friends of mine (both retired programmers) have never owned a TV but used to get regular letters and visitors accusing them of various things, until they wrote back saying that if they were contacted again they would sue for harrassment. It worked!

At the office we got a letter a few months back implying that we legally had to sign a form saying we didn't have a TV on the premises. We got a phone call a week or so later asking why we hadn't returned it, and when I said we are willing to fill it in at our standard rates they just said an "enforcement officer" would visit soon. I've not seen them yet! I wouldn't let them through the door without a warrant anyway, and they would be wasting their time because we don't have a TV here!

Gareth