Half an hour later, and BAW9271 is still circling above Aberdeen. I can only guess that either they can't land at Glasgow, or BA don't want their plane stranded at Glasgow and are considering landing somewhere else.
Although BA have also said that "As a precaution we will not operate any flights between London and Scotland on Tuesday May 24 that arrive in Scotland before 2pm or depart from Scotland before 2pm."
So, maybe this is a testing flight?
EDIT: They have enough endurance for another hour and a half, awaiting permission to descend into the danger zone.