You would need one if it was a You Tube livestream of a TV programme. The law says that you need a licence to watch or record television programmes "at the same time, or virtually the same time" as they are shown on television. So you'd need a TV licence to watch a live YouTube stream of a live television channel.
I may be wrong (I often am) but I am sure I read some time ago (a couple of years at least) that the legislation had changed (in line with what exists in some other countries in Europe... certainly here in Italy). This means that if you possess ANY equipment capable of receiving streamed broadcasts or subscription channels then you have to have a licence. So if you have PC Laptop iPad and an internet connection, the authorities can easily identify that you have access via your ISP (regardless of whether or not you use it). The Italian Govt. went one stage further adopting an 'opt-out'.methodology... Due to the huge numbers of people that did not pay, they lowered the price of the licence (from 130 to 100 euros) and then made the payment automatic by adding it to the first 3 Electricity bill instalments ( unless you opted out by proving you had no access). They calculated they gained significantly in revenue this way. The fact that Italian Free to air TV is pretty abysmal is 'bye-the-bye' you just have to 'suck it up' Virtually the only TV I watch is Channel 8 F1 GP 'highlights'(actually the 'quali' and unedited entire race) So I could argue I do get my 'moneysworth'. Otherwise it is home cinema, Netflix and Prime (mostly in winter).
No that isn't true. You only need a TV licence if you watch any live TV, or watch any BBC services on demand. Having the equipment alone doesn't mean you need a licence.
No definitely not here. On that ruling, everyone with a smart phone would need a tv licence. It's like @TitusMagee said. I regularly got letters from tv licensing in my first year at uni threatening fines, visits etc for 'not having a licence'. But I did have one. And every student in my apartment block (one floor, 6 people) needed one regardless of the fact we had a shared living room with a tv in it (and in my view should have only needed one licence between us. But because we each had our own bedroom we needed individual licences. So the letters were a joke really, I bet they sent one to every student but it was the volume of letters that annoyed me. I also dont think they can detect whether you watch/dont watch tv as much as they make out here.