bookworm: Were the crew aware, when they made the decision to continue the flight from LAX, that they would need, some 11 hours later, to declare an emergency and land at MAN rather than LHR?
...
If the answer is "no", which seems much more likely, then someone or something got the fuel sums wrong in deciding that continuation to LHR was reasonable.
Or perhaps conditions during the rest of the flight were not as favourable as expected at the time the (otherwise impeccable) continuation decision was made? Things do change as you're chugging along, you know. And when things do change and you can't maintain plan A, then diverting in accordance with plan B seems to be perfectly proper.
At least to this interested SLF who's been reading this ever-lengthening thread with alternating interest and disgust. (I'll leave you to work out which bits of apparent hysteria have provoked the latter.)