Thank you!
It is frustrating though that even the reservation offices have no workaround for this. :-(
This is a Hang Up and Call Again.
The IT wizards changed this area to allow better access for BA service centres, which until recently could not process online upgrades since they were supposed to be, well, online. However in making that change POUG online has become unstable, and they are working to fix this. I would ring Newcastle in the morning if I were you, the +44 191 number sequences, since they know about it, and can resolve your upgrade.