A thought came to me yesterday evening and it was this...If 90% of the long-haul (perhaps SH also) flights are cargo flights and the cabin is full of cargo, how are they unloaded at LHR. I'm assuming that they park at the gates at the various terminals, so underbelly containers would come out as normal, but how about the large cabin loads ? Airbridge seems too complicated, perhaps a catering truck with telescopic capabilities ? Whichever, it must be very labour-intensive.
Also, I caught the Air China 747 coming into LHR yesterday afternoon. I haven't seen one of those in a good while, or at least it seems that way.