I'd say don't believe the prompt.
I'm certain when I looked at on demand when I had v6 that every film that I wanted to watch was UHD and every film said subscribe to get the UHD.
And then when I subscribed there's only literally two pages of UHD sci-fi movies.
I don't believe the logo on the V6 boxes actually mean that the content is available on the 360 boxes.
Also to manage expectations.... It's not like 4k Netflix let alone UHD blu ray. I think bitrate issues and long suspect Virgin paying sky for resolution but not mandating minimum bitrate in their contract