If you have fibre or superfast adsl, bt tech have confirmed, after I asked last week, that the Youtube 4k FREE stream, will be broadcast without error compression via YT, so when you have the stream up and stable on Wed for the final, simply pause the Full HD stream in chrome canary or beta browser, choose 4K, wait a few seconds and then restart the stream, this will be the same quality top of the pops stream, bar one, that can transpose on the YT media servers, not the fake 4k (2k) stream that is the most you can see (mostly) without YT red subscription