Okay, so to add to this, I tried with VM...
Exactly the same story, flat above? Can order 350mbit, my flat below? "Not in a VM area".
I'm starting to wonder if the UPRN is horribly misaligned with geographical location.
Easy fix on Virgin, they just need the House Files team to add the property to the database, they will only do that if it’s listed by Royal Mail. Of course getting a sales person who wants to do anything other than sell is another story.