The fight over Heathrow has stymied successive governments. Yet another commission is scheduled to emerge by year’s end with an “interim report” ordered up by the current coalition government, which halted Heathrow expansion plans originally approved in 2010. The delays have been enormously frustrating, too, to major commercial players like British Airways, which uses Heathrow as a hub and is critical of the fees it charges; it also sees other airlines like Air France and Emirates expanding.

Alternatives have been proposed, most recently by the mayor of London, Boris Johnson, who has suggested closing Heathrow, turning the site into another suburb for up to 300,000 houses (given the shortage of affordable housing in and around the capital) and building a large new airport with multiple runways on recovered land in the Thames estuary.

Just last month, a consortium created by the mayor revealed further fancy design plans for a six-runway airport, which would bring aircraft over the estuary, rather than over heavily residential areas, and would be connected to London by new high-speed rail and highway improvements.

The suggested location is in the middle of the Thames estuary, about 50 miles east of central London; not only could more aircraft land there, they could do so 24 hours a day. The designers claim that such a new airport could be built in seven years and handle 172 million passengers annually. Heathrow this year will handle about 71.6 million passengers, 31.8 percent of the passengers at all British airports.

Gatwick, which is 30 miles south of London and wants a second runway, is about half as busy as Heathrow, followed by Manchester, Stansted and Luton. But there are significant problems involved in expanding any of the other airports close to London, and debate rages over whether competition among Heathrow, Gatwick and Stansted might better serve passengers.

While an estuary airport seems attractive, the problem is, as ever, money. The cost of this latest proposal is estimated at £47.4 billion, about $77.6 billion, but who knows what it might finally cost, counting new transport links, while an inland expansion of Heathrow has been held back by noise and politics. (Estimates for a third runway at Heathrow are £14 billion to £18 billion, or $22.9 billion to $29.5 billion.)

Given the uncertainty, major airlines want to stay at Heathrow, including British Airways, its Oneworld alliance and its major rivals in the Star Alliance, which includes United and Lufthansa, and SkyTeam, which includes Delta Air Lines and Air France.