A shortlist of airport expansion options that could include a third runway at Heathrow is being announced today by a government-appointed commission.
New runways at Gatwick and Stansted airports could also be on the list in the first report of the commission which is chaired by former Financial Services Authority chief Sir Howard Davies.
London mayor Boris Johnson, who is bitterly opposed to expansion at Heathrow will be hoping that his preferred new Thames Estuary airport plan - dubbed "Boris Island" - makes the Davies shortlist.
Sir Howard's team will also announce measures to deal with capacity problems in the short term. These could include making more use of the two existing runways at Heathrow where homes will be lost if a new runway is built.
But there will be no firm, long-term announcements or final runway decisions in today's report. Those will come when the commission makes its final report in summer 2015 - after the next General Election.
As with the HS2 high-speed rail project, the airport expansion debate has been heated. While bosses at both Heathrow and Gatwick have made the case for runway expansion, Mr Johnson has described the building of a third runway at Heathrow as "environmentally disastrous and wrong for London and the UK".
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 from the Prime Minister to back Heathrow expansion would represent an "off-the-scale betrayal" and that Mr 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 any decision would come after summer 2015.
He said the decision would be in the best interests of the UK, not just London, and pointed out that aircraft are becoming quieter and more fuel-efficient.
Yesterday, House of Commons Transport Committee chairman Louise Ellman gave a reminder that her committee had backed a third, and even a possible fourth, runway at Heathrow while rejecting the Boris Island scheme.
Heathrow bosses and many business groups have argued that Heathrow is already full and UK competitiveness will be lost if the country's largest airport is not expanded.
In a speech in October this year revealing the commission's "emerging thinking", Sir Howard said: "Our provisional conclusion is that we will need some net additional runway capacity in the south-east of England in the coming decades.
"To rely only on runways currently in operation would be likely to produce a distinctly sub-optimal solution for passengers, connectivity and the economy and would also almost certainly not be the best solution in terms of minimising the overall carbon impact of flights and travel to and from airports."