 The plan could virtually make Heathrow and Gatwick into a single hub.In 2018 a proposal was put forward by a British engineering consultancy, Expedition Engineering, for HS4Air, a high-speed railway line that would run to the south of Greater London, creating a 140 km link between HS2 and HS1 via Heathrow and Gatwick Airports.Before the year 2000, there had been three types of high speed trains in Britain