A third runway at the UK's biggest airport - Heathrow - is one of the expansion options put forward in a first report published today by the Airports Commission.
A second runway at Gatwick Airport in West Sussex is also on the options shortlist from the Whitehall-appointed commission, which is chaired by former Financial Services Authority chief Sir Howard Davies.
But the commission stopped short of listing Stansted Airport in Essex as a possible extra runway candidate, saying that overall one extra runway would be needed to be operational in south east England by 2030 with a second additional runway likely to be needed to be operational by 2050.
London Mayor Boris Johnson is bitterly opposed to expansion at Heathrow and favours a new airport in the Thames Estuary, dubbed "Boris Island".
Today, the commission said it had not shortlisted any of the Thames Estuary options "because there are too many uncertainties and challenges surrounding them at this stage".
It said it would undertake further study of the Isle of Grain option in the first half of 2014 and "will reach a view later next year on whether that option offers a credible proposal for consideration alongside the other shortlisted options".
The commission said it had not shortlisted proposals for expansion at Stansted or Birmingham Airports. but it added: "There is likely to be a case for considering them as potential options for any second new runway by 2050."
The commission said it had concluded "there is a need for one net additional runway to be in operation in the South East by 2030".
It addded that its analysis also indicated "that there is likely to be a demand case for a second additional runway to be operational by 2050".
Sir Howard's team said it would be taking forward for further detailed study proposals for new runways at two locations:
:: Gatwick: Gatwick Airport Ltd's proposal for a new runway to the south of the existing runway;
:: Heathrow (two options): Heathrow Airport Ltd's proposal for one new 3,500m runway to the north west and Heathrow Hub's proposal to extend the existing northern runway to at least 6,000m, enabling the extended runway to operate as two independent runways.
Mr Johnson said today: "Howard Davies' recognition of the importance of a hub airport to the economy and his decision to include the option of a new hub in the inner estuary on the Isle of Grain is both sensible and pragmatic, and is welcome news for Londoners and for the future competitive needs of the UK population as a whole."
The report also contains recommendations to the Government for immediate action to improve the use of existing runway capacity, including trials at Heathrow of "measures to smooth the early-morning arrival schedule to minimise stacking and delays and to provide more predictable respite for local people".
The commission also wants to see a a package of surface transport improvements, including enhancement of Gatwick Airport railway station and improvements to the rail link between London and Stansted.
Sir Howard's team also called for the establishment of an Independent Noise Authority "to provide expert and impartial advice about the noise impacts of aviation and to facilitate the delivery of future improvements to airspace operations".
This is the first of two reports that the commission will make. The second, when definite runway decisions will be taken, will come in the summer of 2015 - after the next general election.
Launching the report, Sir Howard said: "Decisions on airport capacity are important national strategic choices and must be based upon the best evidence available.
"The commission has undertaken a fresh, comprehensive and transparent study of the issues. This report is the product of extensive consultation, independent analysis and careful consideration by the commissioners."
He went on: "The UK enjoys excellent connectivity today. The capacity challenge is not yet critical but it will become so if no action is taken soon and our analysis clearly supports the provision of one net additional runway by 2030. In the meantime, we encourage the Government to act on our recommendations to make the best of our existing capacity.
"The commission will now focus on the challenge of appraising the three options, further assessing the case for a new airport in the Thames Estuary, and delivering a robust final recommendation to Government in summer 2015."
Heathrow chief executive Colin Matthews said it was "good news" for the British economy that the report recognised the need for a hub airport.
"This country needs a hub because without that we won't have the long-haul connections that we need," he told the BBC Radio 4 Today programme.
He said they would look at the alternative proposal to extend one of the airport's existing runways.
"Of course we think our proposal is the best, we have worked on it really hard. Equally, we'll look at every option that's proposed to learn from it. Moving west does make the airport a bit quieter," he said.
"We need to address the concerns of local residents and make the airport quieter. Going west does make the airport quieter."
The last Labour government had supported a third runway at Heathrow but expansion at the west London airport was ruled out by the coalition Government when it took power in May 2010.
Last week, Tory MP Zac Goldsmith said any decision by the Prime Minister to back Heathrow expansion would represent an "off-the-scale betrayal" and that David Cameron would "never be forgiven in west London".
Transport Secretary Patrick McLoughlin has said the Coalition's pledge was not to build a third runway "in this Parliament" and stressed that any decision would come after summer 2015.
Mr Johnson said: "It is clear that Gatwick is not being considered as a hub airport, meaning a second runway there would only provide temporary relief to Heathrow.
"And that means Sir Howard has effectively told the Government it has two choices - proceed with the creation of a monstrous Heathrow... or proceed with the construction of a new hub in the inner estuary that can be built for the same cost as a four-runway Heathrow, and would bring new jobs, homes, and long-term competitiveness.
"A new airport in the inner estuary is the only credible hub option left, and the only one that would uphold this country's claim to be the natural financial, commercial and economic capital of Europe. By keeping it on the table, Davies is saying you have a choice - between a damaging U- turn or a radical new vision for expansion.
"We will be fighting the former and hailing the latter, and I'd urge the Prime Minister and the Leader of the Opposition to do the same."
A Department for Transport spokesman said: "The Government welcomes the publication of the Airports Commission's interim report. It represents a significant step forward in the commission's work in assessing options for meeting the UK's international aviation needs, ahead of the publication of its final recommendations expected in 2015.
"The Secretary of State for Transport will make an oral statement to Parliament later today."
Brian Ross, economics adviser to the Stop Stansted Expansion group, said: " We are obviously greatly relieved that Stansted is not on the shortlist.
"The environmental consequences of even one extra runway would have been catastrophic and the fact is that there has never been a viable business case for any extra runways at Stansted. The airport currently operates at less than half of its potential capacity.
"We must now show solidarity with the communities around Heathrow and Gatwick and support their efforts in resisting the threat that they now face."
Charlie Cornish, chief executive of Stansted owner MAG (Manchester Airports Group), said: "Stansted welcomes the commission's support for measures to increase capacity at the airport in the short term, including improving rail links between the airport and central London. We also support the commission's finding that Stansted is one of the viable options for a runway beyond 2030.
"Stansted has a bright future; indeed, we are the only London airport that can grow substantially in the next 10 years."
Rodney Chambers, leader of Medway Council in Kent, said: "I am disappointed - we all are - that the commission should consider that we need a further airport here in the South East when we already have adequate extra capacity and it's really using that extra capacity that we need to concentrate on.
"But this estuary airport will be an airport in the wrong place. It is not needed and is far too costly, and I cannot understand why those arguments are not being listened to."