The nearest I get is Stansted, but was there not some guideline about 30 minutes holding fuel required for Heathrow? At the end of the day it is total fuel burn that impacts the bottom line so alternate, final reserve and convenience fuel only matter in terms of the additional cost of carrying it.
Overall some interesting points have come out.
1. The sixties turboprop did the trip with more or less the same time and fuel as a comparable A319/737G
2. The Trident seems to have burned at least twice as much as the Vanguard doing the same job, although I remember it as a much more pleasant experience
I saw recently an estimate that 40% of total airline costs are now made up of fuel, obviously varying quite widely dependent on circumstances. Hopefully a sustained reduction in fuel prices together with modern technology and practices can reduce this and contribute to the survival of our employers.