afaik the onus of proof is on TV licensing.
They would need a court order to gain access to a property.
Strictly speaking, if you have the capability to receive a BBC broadcast (TV live or iPlayer) you are liable to cough up. You don’t need to have the iPlayer app installed.
Frankly, the vast majority do have that capability and the license fee gets paid because the majority of people are “honest” (ignorant of the “law”?) and don’t realise that the chances of getting done are very small.
I believe that the detector vans they used to use were ruled have no legal standing, hence they dropped them.
They work on the, not unreasonable, assumption that every property is so capable/equipped and use postal threats and maybe someone knocking on your door as the deterrent.
If enough people decided not to pay up, the BBC would be in Shit Street and they/the Government might do something to change how the BBC is funded, like making it a commercial station.