London's airports urgently need extra capacity, but finding the best locations for new runways—and deciding if the city needs a single, main hub airport—are likely to be major subjects for debate in the coming years.

All three of London's major airports, Heathrow, Gatwick and Stansted, are making a determined push for expansion in their submissions to the U.K. Airports Commission. The commission, set up by the coalition government in 2012, has begun examining proposals for expansion from airport operators, consultants, environmental groups and airlines and is due to report its findings on short-term improvements in airport capacity later this year.

But while it has a U.K.-wide mandate, the commission's focus is likely to be on the future of Heathrow.

In their submissions, Heathrow Airport Holdings, which runs the airport, says it has whittled down options from consultants and think tanks, eliminating ideas to move to new sites and instead focusing on making the best use of the land close to the airport.

Submissions from the operator unveiled on July 17 revealed three options for the creation of a three-runway Heathrow, with others potentially allowing for a fourth runway beyond 2040. The plans are radical and would likely have major impacts on the surrounding infrastructure and communities. But the operators argue that the costs of their proposals are a fraction of the expense of building a new airport in the Thames estuary, and could be completed in just over a decade, relieving pressure on the two-runway airport which is already close to capacity.

The most familiar of the options is a new runway between Heathrow and the M4 motorway. This option, while the quickest to deliver and the least expensive at roughly £14.3 billion ($22.2 billion), only allows for the construction of a short 2,500-meter (8,200-ft.) runway, limiting capacity growth to 123 million passengers and 702,000 movements a year. The airport argues growth would be better served with two new options —the creation of a 3,500-meter runway in the northwest or southwest corner of the airport. With costs estimated at £16.9 and £17.6 billion, respectively, these options are more “technically challenging,” but Heathrow's operator argues they would be preferable, accommodating 740,000 movements per year and up to 130 million passengers.

Heathrow's proposal points out that the northwest and southwest runway growth options “perform better on noise” than the third option because they are farther west than existing runways, so aircraft on approach to these new runways would be higher over London during the airport's “westerly” mode of operation.

The southwest option is more complex, requiring demolition of the village of Stanwell Moor and the reduction in size of two nearby reservoirs. The northwest runway option would see the elimination of two villages, Harmondsworth and Colnbrook and interestingly, Waterside, the headquarters of British Airways. Both solutions would also require burying parts of the U.K.'s busiest motorway, the M25 Orbital, so runways and taxiways could be built on top.

Heathrow's management also says the options could be mixed to allow a fourth runway; one would put two runways at the northwest site. All options include the development of new terminals and satellite buildings in line with the company's plan of giving the airport a more efficient “toast rack” layout, but the design could result in lengthy taxi times, similar to those seen at Amsterdam's Schiphol Airport.

Nonetheless, Heathrow continues to argue that an airport in the Thames Estuary would be a poor value for the money, and an inferior substitute with a smaller catchment area than Heathrow, resulting in increased travel times for passengers even with a major investment in transport infrastructure.

Heathrow officials argue that a Thames Estuary airport probably wouldn't be operational “before 2034,” and “could cost £70–80 billion, of which at least £25 billion would need to be funded by the taxpayer.”

“Adding capacity at Heathrow avoids the transition costs of moving to a new airport,” says the airport's owner. “The developers of a new hub airport would need to compensate the owners of Heathrow and airlines and airport companies as well as build new towns, schools, and hospitals to service the new airport's workforce.”

The company also claims the construction of the runway would provide economic benefits to the U.K. worth up to £100 billion.

But Gatwick officials have similar ideas for expansion. In proposals delivered to the commission on July 19, they say the U.K. doesn't need a hub airport and that capacity should be delivered across the “constellation” of London airports, not just Heathrow. In its filing, Gatwick Airport argues: “The U.K. does not have, and does not need, a so-called 'mega-hub' airport to maintain its global connectivity and status as one of the best-connected countries in the world.”

“Proponents of mega-hubs overstate the importance of transfer passengers in supporting London and the U.K.'s connectivity . . . Gatwick's further expansion will provide a feeder base that will, in turn, attract additional long-haul operations,” Gatwick officials contend. Airport studies indicate that transfer passengers represent only 13% of those using London's airports.

Gatwick has an advantage; it already has an area south of the airport set aside for runway development. It can also argue that its movements affect fewer urban areas because of the airport's position south of London.

Stansted's new owner, the Manchester Airport Group, is also proposing capacity growth through the creation of a second runway, as well as a four-runway hub airport growing from the current airport site.

The Airport Commission now faces a minefield of conflicting ideas and policies, the nub of which remains whether the U.K. needs to have a single hub airport, or whether the burden of traffic should be more equally shared among a constellation of airports. Later this year, the commission will report its findings and recommendations to improve capacity over the next five years, but its longer-term recommendations won't be announced until the summer of 2015, after the next general election.