Heathrow backed - now it's up to the politicians

The final decision on expanding aviation capacity was always going to be far more to do with politics than economics.

And to understand why, it is worth remembering a pledge made by David Cameron in 2009, with "no ifs or buts".

There would be no new runway at Heathrow, Mr Cameron said.

Deciding that it is time to overturn that pledge would certainly be a difficult one for the Prime Minister to swallow.

And those close to him say that Mr Cameron is well aware of the need for politicians to "keep their promises".

Even if the public aren't always convinced that they do.

Sir Howard has provided some limited wriggle room.

He has said that a second runway at Gatwick is a "credible" and "feasible" option.

But he does make it clear that it would provide nowhere near the economic benefit of a third runway at Heathrow.

The political battle is likely to be long and bloody.

Heathrow certainly has some big political beasts who are sympathetic. George Osborne - ever focused on the UK's "long term economic plan" - is certainly one.

The chancellor was instrumental in putting aviation expansion back on the political agenda after the 2010 election.

And he briefed the Cabinet yesterday on the importance of maintaining the UK's hub airport capacity. Code, some think, for Heathrow, the UK's only hub airport.

Another sympathetic to expansion west of London is thought to be Sajid Javid, the Business Secretary.

Business leaders are already queuing up to back Heathrow, with John Cridland of the CBI saying he wants to see diggers in the ground by 2020.

Ranged against are the high profile political double-act of Boris Johnson, the London Mayor, and Zac Goldsmith, the MP for Richmond Park near Heathrow, who is likely to be the next Conservative candidate to become mayor of London.

Other local MPs, including the international development secretary, Justine Greening, are also firm opponents.

Local residents groups have already launched legal actions against the Commission and are sure to make their feelings known.

Those against Heathrow expansion will scour Sir Howard's report to argue that Gatwick is still a deliverable option.

Certainly fewer houses will be demolished and there will be fewer environmental and noise effects if a second runway is built south of London.

But Sir Howard is clear, arguing that Heathrow is the better option economically.

Whether Mr Cameron can ever bring himself to agree, we should know by the end of the year.