If you UUA as soon as you book that's fine because there's no way to do it as part of an online BAH booking. But I've been warned twice now that the fee was only being waived because I did the upgrade within 24 hours of the original booking.

I think it's always been in the T&Cs but never enforced until relatively recently. So I would never again book a BAH unless the UUA availability was immediately available - holding out for it to open up later could be an expensive change.

Very poor show from BA, IMO...