Interesting experience when I phoned BT to say I no longer wanted their BT TV service. First they offered a generous reduction on BT Infinity, but still charging a (slightly) reduced rate for the TV service. I phoned again, and said I didn't want the TV service, and this time I was offered it for free for a year, including the extra channels. I don't even use their box any more. I am unlikely to watch their extra channels. I noticed one was called History but consisted of reality programs as far as I could see.
So, it is indeed difficult to leave BT TV! I could ring again but am lacking the motivation. I must note in my diary when I next need to renew as they will no doubt try to start charging me from then on.