One-third of Heathrow’s passengers are transfer passengers. These passengers are important because they help to maintain a global network of direct overseas air routes. It is because of these transfer passengers that around two-thirds of all UK long-haul flights depart from Heathrow.

For example, there may not be enough demand in London to support regular, frequent flights to Beijing, but because many transferring passengers pick up the service from Heathrow, this creates enough demand for airlines to operate a frequent long-haul route. This is not just important for the airport business. The bigger the network of its direct air routes, the more attractive a city and a country become to investors. Businesses are able to access a huge number of overseas markets, suppliers, and customers from one location.

Europe’s other major hub airports – Paris, Frankfurt and Amsterdam – are all investing heavily in new capacity in an effort to attract the transfer passengers currently flying through London. If airlines can't fly from Heathrow they will fly from another hub instead, taking their business outside of the UK.

More than half of major companies report that international links are 'absolutely essential' in deciding where to locate their business.