You were lucky and wise to check in some 7 hours before departure and before they suspended check-in at city stations.
Situation is a bit similar today, with check-in closed at 4pm. But it is almost impossible to get through the picketing protesters.

A few other longhaul flights departed last night including a few CX flights.
LHR-HKG flights are full with families returning for school start (many on 15 August), that's probably why BA decides to fly despite the emptu planes on the way back.