Thanks! It turned out that the upgrade was processed but then cancelled due to last minute lack of seats. I received an email from Virgin refunds saying:
We’re really sorry to let you know that since your upgrade request was accepted through Your Bid, availability for your flight has changed and the seats are no longer available for purchase. Every now and again, opportunities for upgrades close more quickly than some of our systems can process, which is what’s happened on this occasion. Please accept our apologies that we haven’t been able to upgrade you this time. We have refunded your money and look forward to welcoming you on board
So I think the moral of the story is, if you see a pre-auth on your CC it doesn't 100% confirm your bid is successful.