The best approach to adopt with any TV licensing guy who comes knocking on your door is to treat him with the contempt he deserves and tell him you're not interested and to go away (you can be more or less polite than that depending upon his attitude
). By the way, they can be devious, as some of the examples on the BBC Resstance website demonstrate, i.e. they'll try to avoid telling you who they actually are for as long as possible.
The TV Licensing propaganda (excuse me, I mean "information"
) is often guilty of gross distortion of the facts. They'll issue dire warnings such as "If you use a TV, you need a license," which is not, strictly speaking true.
You need a license to install and use TV equipment capable of receiving any broadcast originating or controlled from within the U.K. Anything else isn't covered, so you don't need a license to use a TV just to watch pre-recorded tapes or DVDs, for example.
They've also sneaked in some changes in the rules over the years, presumably in the hope of catching somebody out. Check the section on the link Dawn provided about second homes as an example. There's a ridiculous part about being covered by your main license only if the TV is powered by its own internal batteries. That's relatively new. Parts are also just about unenforcable too, such as being covered in a holiday home only if the TV at your main house isn't in use simultaneously.
By far the majority of prosecutions for no license come from people who have allowed one of these TVL rats into their home voluntarily or have admitted to breaking the law when "interviewed" by one. That's why they're so pushy and will try any tactic to get someone to actually talk with them (e.g. sending letters which seem to imply that you are legally obliged to undergo an "interview" with said rat when he comes banging on your door).
The whole tone of TVL in this is really not far removed from "Get a license or we'll send the boys round!"
In short: Don't be intimidated by them; even if you're perfectly legal don't allow them into your house without a warrant; and don't even talk to them other than to tell them to leave your property.