Some very interesting links - thank you Folkiedave!
A STATIC caravan needs its own licence. A TOURING caravan is covered by the householders own licence, as is a garden shed and any number of TVs on the premises.
It is certainly true that you can pick up what is being viewed on any CRT screen using suitable equipment outside of the building: there is sufficient radiated signal. You don't need much signal either: I heard a program recently about the risks of relying on satnav and GPS too much - the signals from satellites are like looking at a 100watt lightbulb from 12,000 miles away or was it 1200 miles?.
Interesting that people buy and use (illegal) jamming equipment for GPS so when it is fitted to company cars and vans (so the company knows where you are at all times) you can take a detour to somewhere and plead the equipment wasn't working at the time. But you blot out everyone elses signal aroundabout too.
So next time your sat nav malfunctions, don't automatically blame the manufacturer!!!