It will be fuel contamination
China has a $2,000,000,0000 a year industry making fakes. Lest you think this is just the odd Rolex or Gucci bag for a laugh the China PLC inventory includes millions of fake parts not caring one whit how many people are killed thereby. More sinister is the the fake pharmaceuticals which often are not simply benign white chalk pills but random chemicals found out back in the garage, once again not caring one whit who or how many die.
In the case at hand the only other remotely possible explanations are a multiple bird strike of epic proportions or fuel exhaustion. Give credence to the former if you like, to the latter, well, you will need a lower opinion of BA aircrew than is common.
No, someone will have passed off a few million litres of doctored diesel fuel as jet fuel. This fake fuel of course is not tested for fuel freezing. Fuel freezing will then have occurred during the lengthy flight from China (not ice formation, but wax components of the fuel reverting to solid) and this slurry sank to the bottom of the tanks. On final with perhaps 4 tons or so sloshing around in near-as-empty tanks this fuel willl have been ingested.
Eh Voila
Have some faith in your hardware is what 10,000 hours on the 777 has taught me. There will be human skulduggery at root here somewhere.