Originally Posted by
BotB
I think you can only upgrade with Avios if you do so at the time of booking on such fares...afterwards they cannot be upgraded with cash or Avios (unless you they offer the cash POUG offers to help them not have to do Op-Ups...)
BotB, I'm 99% sure that I UuA'd after I booked the flights... But it was before coffee o'clock when I did it so I could be (probably am) wrong.