Uncle Fred, the most fuel wasted at LHR is on departure ie. getting airborne off r/w27 with enough fuel to stay at 6,000ft until CLN/DVR before further climb. Easyjet conducted a test on a flight from Stansted to Edinburgh where they were given a much higher level to climb to on departure. I cannot remember the exact figure, but I think it was at least 10% less fuel needed!! Now put those sort of figures to a flight going to the Far East, I know it won't be 10%, but it is a vast difference and a major saving for the airlines.