I am considering entering a bid to upgrade to Upper Class on my LHR-BOS premium economy award ticket booked directly with Virgin Atlantic. The upgrade bid starts at 400 pounds, which I think is a good deal, but mentions additional taxes/surcharges would be charged also but doesn't indicate how much these may be.

When booking a new award ticket the taxes for premium and upper class are the same at 272 pounds but the YQ difference is 250 pounds.

Has anyone done a “Bid to upgrade” on an award ticket that could confirm what (if any) additional surcharges would be charged in addition to the upgrade bid itself? Should I expect to pay the upgrade bid + 250 pounds in additional YQ surcharges?