You need a licence if you are watching or recording TV as it is broadcast. It doesn't matter whether you are using a TV, phone. tablet or PC. That's ANY live TV - not just the BBC.
TVL detector vans may exist, although I have yet to read any coherent explanation of how they work. The BBC refuse to give any info on how they work or how many detectors vans exist, but estimates suggest there are about 5 of them and they dont work anyway , the rest contain a pizza box, sleeping bag and a wank sock. The handheld devices are bollocks too. PDAs with fancy graphics.
You do not have to let the salesman officer into your house unless he has a warrant and is accompanied by the police (TVL procedures say they must have the police with them when executing a warrant). TVL/Capita salesmen officers get paid a £20 commission if they con sell you a licence, so please don't think they are just doing a job. Honesty doesn't pay. Well it pays minimum wage, I suppose, which is why it is wise not to trust the sods.
Never, ever speak to them. If you do speak to them (apart from 'No thank you' ) for Gods sake don't sign anything. Ever. Don't give them your name. (NB it is not illegal to give them a false name, but I really wouldn't talk to them)
If you do get raided they are only allowed to search for tv receiving equipment. And they can't go rifling through your smalls drawer or your bills, unless they're big enough to hide a tuned in, functioning tv. They are not allowed to search your PC, phone, tablets etc (unless they have a warrant under ROIP Act. They won't have) Make sure any TV is disconnected from the aerial and internet, or they may be able to get a live station up and you'll be committing an offence (or they can argue you are). They are NOT allowed to connect the TV up themselves, or ask you to do so (because that would be breaking the law).
Seriously - if you really don't watch live TV the safest option is to not communicate with them in any way. If you follow this simple guideline you have more 100s of times more chance of being burgled than TVL/Capita turning up with a search warrant.
You may have gathered that I am seriously fucked off with the threatening, abusive, duplicitous bastards and I can't bloody wait for the day when they scramble the BBC signal and we can all pay for what we actually watch. Just like I do with Netflix.