I should add to what JB66 has said - Netflix 4K is also available on the V6.
It 'll get interesting with BT Sport 4K, I reckon. BT are raising their prices and taking BT Sport off free for broadband customers. VM increased their prices for TV XL (as it was) in 2015 to accommodate BT Sport as part of the package.
BT will want to screw maximum out of VM for any 4K content - but I'll bet that this is being negotiated right now. Now, will BT refuse so as to improve their competitive chances for Broadband? As I see it, 4K bandwidth on BT Infinity coming down from BT Sport on a broadband connection can have some interesting effects on remaining capacity! Whereas VM's TV comes down its own coax frequencies and doesn't steal from your broadband bandwidth. Something like that!
You tube is an APP, the question was about the BBC red button interactive service.
there is no 4K content on terrestrial (freeview) TV channels
I doubt that showing it in 4k makes the you-tube stuff any less vacuous
last I heard Virgin own zero percent of You tube so it is also true that Virgin have no 4k content of their own.
the V6 can support netflix in 4k and probably could support amazon video, if there as ever an Amazon - Virgin contract put in place. but that is not certain, Amazon do not stream with the same codecs and DRM as Netflix and the V6 may lack the needed hardware decoding for Amazon HEVC