To the poster who got a letter saying they'd be round with a warrant - that is extremely unlikely! It's just another scare tactic.
I can't find the info at the moment as on my phone, but when someone ut a Freedom Of Information Request in to find out how many search warrants had been granted ever, the number was something ridiculously low (I think it was 5 but may be wrong).The chances are that they will not waste money obtaining a search warrant as it would cost them a lot of money if they are not certain that you watch live TV.
Pretty much 100% of people who are prosecuted for licence evasion have just let them in to check, thinking that they had to, or they've been daft and had their TV on within sight of the front window, then denied having a TV.
I notified them about seven years ago that I didn't need a licence due to not watching live TV - at that time I did watch iPlayer very occasionally, but didn't need a licence then to do that. I heard nothing from them except for a form to complete if I still didn't need a licence every two years.
At my previous home, they had the address mangled up with the neighbours, so I had a huge skinhead bouncer type guy on the doorstep. I would have been terrified tbh if I wasn't 100% sure I had a licence and was able to go and get it to show him. He was actually lovely, and said he'd let them know to sort their database out.
A disabled friend of mine, who also has MH issues, regularly gets really scary sounding letters from them. He has asked me to drive him to the post office to buy a licence several times before, as he's convinced they are taking him to court and he'll be locked up forever. He doesn't even own a TV or computer! I have to reassure him every time a letter comes - have complained as it is harassment and he is very vulnerable, but they still persist. It really pisses me off that they can get away with this.