Thank you for the link, Christine.
So, it seems to be the not-uncommon situation of a London agent or importer registering the design in Britain, but the actual manufacture being carried out elsewhere (probably Czechoslovakia in this case), then the glassware imported to Britain for re-sale.
Sadly, I have still do not managed to acquire a copy of the Blue Book, but it might be interesting to see if there were any more Vitrea-registered designs.
Fred.