thanks all - I am indeed HBO with a mobile BP, so will enjoy the sunshine.
and apologies for not mentioning that BA55 was the LHR-JNB, I wasn't sure if that would change anything.
EDIT to add: this is the 380 service, according to FR due to be
operated by G-XLEH, which is currently en route from LAX, and
due in only 10 minutes late... so not quite sure why we have a delay posted.