If you have any kind of equipment that can receive tv broadcasts, you're supposed to have a licence. If a licensing inspector knocks on your door, and asks if you have a licence, you either say 'yes', in which case he'll ask to see it; or you say 'no', in which case he'll ask if you have any tv-receiving equipment. He might ask to enter your house and have a look around. He won't know if you've been watching iplayer, or anything else. If you have the equipment, but no licence, he might issue a summons.