I think fuel was also an issue.
A mate of mine said that BA organised their own reserves at FVHA at the height of 'heaven' ('heaven('t) got fuel, 'heaven got electricity, 'heaven got water, 'heaven got bread etc etc), but such reserves were on occasion prone to 'unauthorised borrowing' from Govt to operate VIP flights, leaving BA no guarantee of being able to use their own supply to fuel the return sector.