You must ask yourself what is the reason that people in London have more money. Purchasing power is not something that manifests itself out of thin air, as well as exchange rates of money.
An economy in which the people have multiple times the purchasing power must do something right. And moving people in that economy around is more valuable than moving people elsewhere.
An economy in which the people have multiple times the purchasing power must do something right. And moving people in that economy around is more valuable than moving people elsewhere.