LONDON — Support is growing for constructing a brand-new London airport in the Thames Estuary region of southeast England, the capital's mayor said Wednesday.

Boris Johnson said the government was "increasingly interested" in the ambitious proposal, which would see a massive new air hub built where London's River Thames meets the North Sea. Although detailed plans are likely to be years in the making, one high-profile proposal would see a 150 million passenger-a-year airport built at the edge of the sea for 50 billion pounds ($76 billion).

Johnson acknowledged that building an entirely new airport would be costly and time-consuming, but he argued it was critical to the country's economy.

"You can't go on expecting Britain to compete with France and Germany and other European countries when you simply can't supply the flights to these growth destinations," he told BBC radio.

Johnson's new airport would effectively replace Heathrow, London's current long-haul hub. The airport handles 65 million passengers annually, making it Europe's busiest, but longstanding plans to build a third runway there were scrapped following a drawn-out and acrimonious debate with local residents and environmental groups.

Gert Zonneveld, a transport analyst at Panmure Gordon, said that the capital's other four airports are either too small or too dominated by short-haul, low-cost carriers to take on Heathrow's role.

That has led Johnson to champion an entirely new airport built about 40 miles (65 kilometers) southeast of central London. A proposal recently published by London-based Foster & Partners envisions a multi-runway facility on the Isle of Grain, a marshy, sparsely populated peninsula at the edge of the estuary.

The airport would be linked to London by a four-track, high-speed train line which would plug into the Channel tunnel rail link and a planned high-speed line to Birmingham. Concept drawings published by the architecture firm show bullet trains pulling into a glass-domed terminal building at a massive airport at the edge of the sea, as well as a futuristic-looking flood-protection barrier aimed at generating tidal power for the region.

Critics say the plan is expensive, impractical, dangerous and environmentally destructive.

Foster & Partners' proposed price tag of 50 billion pounds is nearly half the size of Britain's budget deficit. Local council leaders have expressed outrage, saying the airport would be on the wrong side of London and that flight paths would slice through an area which is home to thousands of migratory birds.

The fact that the Isle of Grain also handles a fifth of Britain's liquefied natural gas imports has raised safety concerns, and there's a further danger lurking just below the surface of the water: The SS Richard Montgomery, a World War II-era American munitions ship, remains submerged with 1,400 tons of explosives only four miles from the proposed terminal building.

The government is planning to soon publish proposals for a possible expansion of Britain's airports, a spokeswoman for British Prime Minister David Cameron's office said Wednesday. The consultation is expected to include proposals for a new London hub, including Johnson's estuary idea.

Zonneveld said that technical challenges could be overcome — but suggested that cost would be the biggest stumbling block.

"From an engineering point of view, yeah sure it could be done," he said. "Clearly it needs to be paid for."

Associated Press writer David Stringer contributed to this report.


Foster & Partners' proposal:

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