A short-list of options for extra runways at UK airports is set to be included in the first report of the Government-appointed Airports Commission this week.
And for the short term the commission will also propose changes such as making more use of existing runways until the long-term expansion plans can be fulfilled.
There has been much speculation that the commission, chaired by former Financial Services Authority chief Sir Howard Davies, will include in its options a third runway, or possibly even a fourth, at Heathrow in west London.
London Mayor Boris Johnson, who favours a brand new Thames Estuary airport dubbed "Boris Island", said last week that Heathrow expansion was "environmentally disastrous" and "bad for London and the country".
And last Friday, Tory MP Zac Goldsmith, whose Richmond Park & North Kingston seat in west London would be affected by the growth of Heathrow, said any decision by Prime Minister David Cameron to back Heathrow expansion would represent an "off-the-scale-betrayal" .
Although supported by the last Labour government, expansion at Heathrow in the form of a third runway was, initially, ruled out by the coalition Government in May 2010.
Mr Johnson said last week: "I've long thought that the purpose of the exercise (in setting up the commission) was to provide cover for a U-turn on Heathrow. "
Mr Goldsmith said: "David Cameron himself has to really think very carefully about this. Politically a U-turn on this issue would be catastrophic for him. You have to remember it wasn't just a few party speeches, David Cameron went to every single constituency affected and stood up and said 'no ifs, no buts, there will be no Heathrow expansion'.
"If he does a U-turn on this issue it would be an off-the-scale betrayal and he will never be forgiven in west London.
While Mr Johnson and Mr Goldsmith remain vehemently opposed to Heathrow expansion, bosses of the airport and those working there are equally passionate about a new runway at the west London airport.
Similarly there is strong support by management at Gatwick for an extra, second, runway at the West Sussex airport, while the option of another runway at Stansted has its supporters.
Sir Howard's final report, when the commission is expected to make firm proposals on just where the expansion should best take place, is not due until summer 2015 - after the next general election.
With there being no need for a definite decision for more than 18 months, the commission could choose to list a number of options in its report on Tuesday, while saying that nothing has been ruled in nor ruled out.
Should the Boris Island scheme not even make the short-list then it will almost certainly signal the end of that particular Estuary plan.
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."