Was it always the case that the GUF holder had to be one of the travellers on the booking? I thought not, but maybe I'm mixing it up with the GGL joker, for which the GGL member definitely doesn't need to be one of the travellers.

It says the upgrade is subject to availability, but doesn't say what that actually means. Historically it's meant availability in I for Club or A for First when booking through a travel agent, but it's not clear whether this will now be the case for upgrades made processed through BA.

I'll probably stick to making my GUF bookings entirely with a travel agent as the extra Avios and TPs for the higher cabin tend to post when doing it this way, whereas they might not if upgrading through BA.