As an update, 5 out of 8 First seats were empty on the flight but BA still didn’t release any Avios upgrades! They were selling airport upgrades at a very reasonable price (£400 ex-Delhi), and I succumbed particularly because I wanted to try out the new cabin on the 787-9.
BA, along with other airlines, is systematically devaluing its FFP programme. I find miles seats and upgrades increasingly difficult to obtain, and other comments on this thread bear that out. The counter to that is that I’m no longer influenced by FFP status or carrier loyalty, and now shop around for the best fare. All my Gold card seems to give me is an extra bag, and I hardly ever need that now.
Thank you all for your very helpful suggestions and comments.