The DELAYED BA001 departed today at 13:10 from Terminal 4.
I guess they ran out of time last night to get out of LHR before the evening noise regs would make the departure impossible.
10 out of 10 to BA for flying the service and not disapointing anyone. Had this happened a year or 2 back, they would have simply cancelled the flight and re-booked the pax on another subsonic service.