It occured to me last night that the only way the supply tanks could have emptied to zero and 0.4kg, the contents reported by the AAIB, would have been if the aircraft was standing on its nose, which of course it wasn't. Fuel could have spilled out of the supply tanks at the angle at which it was lodged in the pub, but there would have to have been fuel in the tanks to start with, and it wouldnt have been able to drain down to zero and 0.4kg at that angle.
Returning to the question of left/right asymetry, I do still think cross fence spillage remains a viable explanation for two flameouts in much quicker succession than expected.