Thanks for that clear explanation, I was as surprised as MU3001A, but discovering that specific BA procedure (?), AAIB report makes now more sense.
What still does not make any sense considering that almost simultaneous double eng similar misbehaving:
1- "total fuel on board was indicating 10500 kg" ... but no mention of the actual FOB retrieved from the main tanks ?
2- "the fuel crossfeed valves indicated that they were closed" ...but no mention they have been physically checked closed ?
Also:
- What could justify that amazing 5% reduction over the planned fuel burn ?
- Did the engines actually spool up somewhere in the hold ?