Mayor Johnson welcomes Foster’s agreement that “the answer to Britain’s aviation needs lie in the estuary.” Transport for London, controlled by the mayor, is within weeks of publishing its own report on potential locations in the estuary for a new hub airport. However, both Foster’s and the mayor’s plans are dismissed by critics, including the not-for-profit Royal Society for the Protection of Birds (RSPB).

Building on such a scale in the estuary would damage an area important for bird migration, says RSPB spokesman Andre Farrar. He also questions the wisdom of building an airport in an estuary “full of large, flapping birds.” But he doubts that either scheme will take off. “For 40 years we have seen proposal after proposal,” he notes.

Nevertheless, with Heathrow operating at 98% capacity and an official ban on new runways at other major existing airports in southeast England, the government is not ruling out an estuary option. The Dept. for Transport last month completed a consultation of stakeholders and plans to publish draft legislation setting out London’s aviation future next year.