Outlook Let's not get into the rights and wrongs of a third runway at Heathrow. Whatever the commercial case for and against, it is as plain as a pike staff it's not going to happen. Only Gordon "I've saved the world" Brown could believe the Government still capable of bulldozing through a proposal that seems to be opposed by just about everyone other than the big airlines, American investment banks and the virtually bust owners of Heathrow itself.

Never mind that virtually all those columnists who write with such passion on this issue in the mainstream British press seem to have a vested interest, in that they live beneath the Heathrow flight path, or that the net effect on climate change if the runway isn't built will be precisely zero (the traffic will merely go somewhere else), politics is about the art of the possible and the only person who seems not to have realised this is Mr Brown.

The case for a third runway may or may not be a good one, but the fact is that the Government has already lost it. To push ahead in the face of such opposition is political madness. Given that the Conservatives have already pledged to reverse the decision as soon as they get into power, nobody is going to spend even so much as a penny preparing for such a project. It's going to take at least five years to get through planning procedures, so even if Mr Brown wins the next election, little if anything will have happened by the time we get to the following one. In the meantime, the decision will probably have cost him anything up to 30 seats. The Government hopes to win brownie points with big business for the "bravery" of its decision, yet I doubt anyone outside the City gives a toss about the future of Heathrow, an airport whose defiance of the prevailing westerly winds meant that it was always in the wrong place for a major conurbation.

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Rather than continuing with a doomed endeavour, policymakers should instead be applying themselves to the alternatives. For Geoff Hoon, the Transport Secretary, to assert that it would "damage our economy" to duck the decision is nonsense. The folly is rather in basing your whole transport policy around an objective that is never going to be realised.

Nor was his attempt to sugar the pill by promising to limit the new slots to the cleanest planes, as well as set new aircraft emission targets, in the least bit convincing. These objectives should be happening regardless of whether there is a third runway at Heathrow involved.

As for promising to maintain so-called "mixed mode" use of runways – whereby landing is switched midway through the day between Heathrow's two existing runways so as to give residents a break from the noise – this is precisely the wrong approach. Heathrow's immediate capacity constraints could be fixed overnight by allowing coincidental take-off and landing on both runways, as occurs in virtually every other major international airport.

And the alternatives? The idea of a brand new airport on the Thames estuary is cloud cuckoo land. If planning for such a monster had begun 30 years ago or more, then maybe, but with the future growth of aviation ever more uncertain, it would be bonkers to embark on it now. A third runway at Heathrow looks difficult to impossible, but the idea of an entirely new airport is just laughable.

The solution to Britain's airport needs must lie instead in a piecemeal approach, with expansion to capacity taking place at a number of existing airports around London – perhaps a second runway at Gatwick or Luton, or even back to the original plan of a second runway at Stansted. There are also lots of accessible smaller airports around London capable of development. There is no reason why, if air traffic continues to expand, it all has to be concentrated into one place.