It's pretty stupid. The original idea was that they wanted a state broadcaster (to prove the're a real big-boy country like all the other ones). But taxing everyone to fund something only rich people have access to didn't sound great, so they decided to just tax rich people for it. ~70 years on and the state broadcaster is an overpriced joke awash in an ocean of cheaper, better competition, but we still have to keep paying for it because no government is willing to deep throat the political shotgun required to end all those public jobs. It's funded by both taxes and tv licences, and even then it's not enough so they want to start charging everyone with a "device that can access the internet."