Investigators have ruled out mechanical engine failure as the cause of the crash landing by a British Airways Boeing 777 at Heathrow last month and are focusing on the fuel system.

The investigation is examining damage to the fuel pumps and the possibility that fuel was restricted in some way or pumped at too low a pressure and mixed with too much oxygen.

An interim report by the Air Accidents Investigation Branch of the Department for Transport said the evidence points to “a restriction in the fuel supply or excessive aeration of the fuel”.

Investigators report some evidence of debris in the fuel tanks and are considering its relevance. They will now seek to replicate the damage to the pumps and match it to evidence of what happened on the aircraft.

The BA flight from Beijing came close to disaster just two miles from Heathrow when the pilots found both engines unresponsive and dropped to the ground short of the runway. Miraculously, only eight passengers suffered minor injuries and one a broken leg. A full accident report may still be a year away.