The theory on the part of the floor at Lloyd's (as of last week) is that it ain't the fuel that caused it, it's "RF interference". The theory goes that after George Brown was dropped off at Heathrow, his driver, or some other entity either deliberately or accidentally forgot to switch off their "jammer" and that the aforesaid vehicle on it's return journey may have gotten within "range" of the affected B777 and caused the mischief.
Maybe he's right; after all, whoever was dropping off the corpse of a long-dead Labour Foreign Secretary of the 1960s at LHR must have been up to something!