Doug E - would you not be 'padding out' for, say, the 'rush hour' at LHR? I think I would - but then I'm not fussed about biscuits...
It is also worth remembering that in BC's 'day' there was far less pressure on fuel costs and also no option to dispense with alternates, so maybe the Vanguard 'standard' figure is not really 'excessive' PLUS that the figure would have been for
all pax/cargo loads and time of day and would be designed to avoid the need for an expensive top-up of a few 100kg, and thus be 'generous'. As for the ground-hogger, well, construct an a/c like a brick-bulit khazi and.........
BC - out of interest, what was the BEA Vanguard seating?