Airports of London cannot be expanded due to the docks on either side. It is also the only airport serving London which does not operate at night. A light rail service from London City Airport DLR station, which adjoins the terminal building of London City Airport, links it to the financial district of the City of London at Bank and Monument stations, which offer interchanges with London Underground. Located in the London Borough of Hillingdon, Heathrow is by far the largest of London's airports and considered the main gateway into the United Kingdom for non-European visitors. Heathrow has four terminals and two parallel
Airports Commission interests, when invited to complete the Airports Commission's Register of Interests. London, with six commercial airports in its metropolitan area, has the world's busiest airports system. However the question of how to expand the capacity of the system to cope with growing air travel demand is an issue that successive governments have failed to address since the 1950s. A previous commission – the Commission on the Third London Airport chaired by Eustace Roskill – sat between 1968 and 1971 and recommended that a site at Cublington in Buckinghamshire (to the north west of London) should be developed as London's third