BA B777 Incident @ Heathrow
Hi
Perhaps a likely reason for two engines to fail (presumably near / or at the same time [only going from what I have read]) would be fuel starvation. Being at the end of the flight, this would seem at least a possible area. If it was unexpected (as it seems it was), it could have been faulty readings of fuel remaining and or / combination of an error in fuel loading somewhere along the line. Just thoughts out loud - most likely it will be something entirely different and a more complex series of events.... first time poster.
Regards
Jason