I'm surprised at their priority list...

At handover to the airport, a telex list will be sent by DUT, which will show the priority of people to upgrade if necessary.
The order of these are:
1.Staff not in their cabin of eligibility (bookable and premium standby)
2.Space Available requests that are still outstanding
3.A list of prioritised passengers if further operational upgrades are required (in oversales situations)

Also, it's not quite clear what a space-available UG is - can any BA insiders elaborate? It sounds as if this might be along the lines of 'something dreadful happened last flight and so this person should be UG next flight' but I may have got that arse about face.