Point 4:
It's the RF emissions referred to in Point 3 which make it possible to detect the presence of TV sets (often even when they're only in 'standby' mode). 40 years ago, when I was involved with our school electronics club, one of our projects was to investigate and make devices which could detect TV and radio sets, and tell the difference between them and other electronic devices. If a few teenagers could manage to do so then, there seems to be a very good chance that communications experts can do so now!
Point 5:
It has been stated above that TV licensing officials have no power to enter anyone's home. Of course, if you leave your door unlocked, ANYONE can legally enter your home at any time. (Trespass, per se, is not a criminal offence). Even if we ignore that, licensing officials can still seek a warrant, under Section 366 of the Licensing Act 2003, if they can show grounds for suspecting that a TV is being used (or has simply been installed) without a licence. That could be the evidence from a detector van or, possibly, from the records submitted by the shop which sold you the TV set.
Chris