"From the accounts so far it appears as though the most likely reason for the problem was either engines, electronics or fuel" (quote)
I would eliminate the engines as an option. It is basically impossible the two totally independent engines failed to respond, at exactly the same time, after many hours of perfect functioning.
It will be possibly a fuel related issue or an electronic/software glitch (which started earlier along the wires, not far from the cockpit) or a combination of these two factors. Software/Hardware within the engines cannot fail simultaneously instead (e.g FADEC).
This incident has sent a few strong messages out (in my modest opinion):
-Grass before/after/around the runway is essential, especially in
RESA. The 27L RESA saved this 777 and we have had a few incidents in the last few years where RESA (combined to pilot's skills or errors) saved lives.
Modern aircrafts have very strong and flexible structures, they can definitely survive a crash-land on grass: RESA regulations/limitations should be possibly be reviewed on all runways and extended whenever possible. Some very profitable car parks will have to be moved (e.g. the one just in front of 27R! at EGLL).
On some aircraft types the windows on doors, where Cabin Crew sit (e.g. on Boeing 767, 777),
are extremely small (it is impossible to see outside! Try it!) whilst CC should be able to see what is happening outside in emergencies,they can be in charge of an evacuation when pilots are unable to PA. On this 777 pax told CC what was going on outside. This is in my opinion unacceptable and you can waste valuable seconds.
Ground-Cameras should be installed on all approaches, capable of recording all final approaches and touch down: the cost of this is nowdays extremely low and they would really help an investigation.
The Pilots did an excellent job. Well done.
Pilots skills, RESA and the 777 solid structure saved many lives at EGLL...