Heathrow or Gatwick: Final decision could be two years away
If the history of UK infrastructure tells us anything, deciding to build something is a very different proposition to actually doing it.
That is particularly true around the thorny and politically toxic issue of aviation.
The government has said it will make a decision by the end of the month on its preferred option for expansion at either Gatwick, or a new or extended runway at Heathrow.
While the expansion hawks want a new runway at Heathrow now - whatever the government's decision next week - the process up to construction will not be quick.
The previous Transport Secretary, Patrick McLoughlin, outlined last February to the Transport Select Committee what would happen once a decision was made.
He said: "...there will be a draft National Policy Statement (NPS) published for consultation and laid in Parliament. This is published a minimum of four weeks after the announcement on the runway location to avoid the legal risk of pre-determination.
"There is no decision yet on the length of the public consultation, but it could be 16 weeks. A Commons Select Committee will examine the draft NPS and hold a full-blown inquiry for 12 weeks immediately following the public consultation.
"The Commons Select Committee will submit a report to me by the end of the 12-week period. Once a final NPS is laid, debates and votes must happen within 21 sitting days of the House. At any time after the vote, or it could be the same day, if there is a negative vote, the Secretary of State will change and lay a new NPS, again for 21 voting days."
So, there will be around a year before Parliament gets a vote on that National Policy Statement. The Government will be expected to address concerns over noise and pollution.
And it is then, and only then, that it enters the planning process.
First the developer submits a development to the planning inspectorate. Then there is a planning inquiry over six months. Then the planning inspector reports to the Secretary of State within three months.
And finally the Secretary of State will consider the report and announce a decision within a further three months.
So an actual "final" announcement could be two years from the initial Government decision - and that is with a fair wind.
There will be gaps and delays in the process, there are those who think two years is the absolute minimum and the reality is it will take at least four years before a "final decision".
None of the timescales include the legal challenges that could slow down the process further. (Bear in mind this is meant to be a quicker process than was in place previously).
History tells us how difficult it is to build new runways in the South East and how strong the opposition is.
There have been many inquiries, commissions and consultations. Plans have come and gone. There have been proposals at Cublington in Buckinghamshire, Maplin Sands in the Estuary, Stansted and the previous Northern runway at Heathrow.
All fell off the table during the long process as the politics shifted. Even Labour, with its large majority under Tony Blair, could not get far enough through the process to build at Heathrow.
Recently, Howard Davies - in charge of the latest Airports Commission - perhaps pertinently noted: "The London airport capacity problem has perplexed governments for over 50 years, for reasons that are not hard to find.
"The considerable benefits of aviation accrue to the many, while the environmental costs are borne by the (relatively) few. For those who live near them airports are noisy neighbours and are greedy for space.
"In a congested corner of a crowded island it is not easy to find a good home for them. No new full-length runway has been laid down in the South East of England since the 1940s."
So after the decision is made next week, it is not the end at all. It is really just another beginning.