Contrast this to19M transit passengers or as I describe them freeloaders, who fly in ,then fly off into Europe, who do not pay any APD, infact we are lucky if they buy so much as a burger as they dash to their connection !
Although those 19M transit passengers have mostly paid their fares to British airlines, thus pumping money into the British economy and corporation taxes to the British government. Saying that transit passengers don't contribute to the British economy is like saying the City of London doesn't contribute because two foreign parties may choose to do business with each other there through a British intermediary.