According to the BBC reportIn its update, the AAIB said the Boeing's twin Rolls-Royce engines initially responded to the request for thrust, but after three seconds the thrust of the right engine reduced and after eight seconds there was a thrust reduction in the left one.
Recorded data shows the aircraft had enough fuel and its automatic throttle and engine control systems had worked as expected, the AAIB said.
Yet: Both engines [...] were still running when it came down
This is really beginning to sound like a fuel system problem to me. I assume they're now double checking to see whether there really was sufficient fuel in the tanks. After that, I'd be looking at the fuel pumps.