Leading article: The runway that will never take off

There is not much doubt what the Government's decision about a third runway for Heathrow will be. This week, Geoff Hoon, the Transport Secretary, with the support of the Prime Minister, is likely to give the go-ahead to the expansion. Equally, however, there can be little doubt that the third runway will never be built.

Nor should it be, and Gordon Brown would earn some respect for doing the right thing, rather than simply allowing the recession and European Union law on pollution to do it for him.

Instead, this week's announcement is likely to employ a version of that classic Brownian device, the Five Tests. Famously, it was the tactic by which Mr Brown as Chancellor retained control of the decision on the euro. But he also used it to try to finesse a divided Cabinet over the Millennium Dome, saying that it should go ahead if it met five rather spurious conditions.

So we should expect the third runway to be approved, when the Cabinet makes its formal decision on Tuesday, on condition that it satisfies certain tests, notably of its environmental impact. Those tests provide the glue that keeps the Cabinet together. Hilary Benn, Secretary of State for the Environment, said last month: "We have to achieve the environmental objectives; we have to honour that commitment and I am determined that we will."

We trust that Mr Benn has secured reliable guarantees. BAA has proved slippery in the past. Sir John Egan, its former boss, said that Terminal Five would not add to pressure for a third runway. Last week, BAA admitted: "That's what he had to say to get permission for Terminal Five."

The harder the bargain that Mr Benn has struck, the more painlessly this polluting, climate-changing and unnecessary project can be abandoned. As Geoffrey Lean, our Environment Editor, reports today, Heathrow airport already breaches the limits that will be set by European anti-pollution law. Despite the enthusiasm of, for example, proponents of planes powered by algae, there is no realistic chance that an even larger airport could comply with that law.

That is, however, to rely on one piece of environmental law to achieve a higher green goal. The big argument against Heathrow expansion is not that it will make local pollution worse, although it will, but that it undermines every other effort that this country ought to be making to reduce its contribution to global warming.

Aviation has been the fastest-growing source of carbon dioxide emissions. The growth of air travel needs to be slowed, and the most effective mechanism is to stop building new capacity. The right response to overcrowding at Heathrow is to put a higher price on landing slots, not to build another runway. That would be a crude way of putting a price on flying that came closer to reflecting its true environmental cost.

Fortunately, it is not only EU pollution law that will finish off plans for a third runway. The recession means that the business case for expansion, always weak, is weaker still, while a poll of six Labour marginals in west London points to the electoral threat it poses to the Government.

More important, perhaps, than a project that is unlikely ever to be built is the equally controversial decision on a new coal-fired power station at Kingsnorth. On this, the Government's decision is harder to predict. Again, a go-ahead is more likely than a No. Again, conditions are likely to be attached. But this time the conditions really matter. They will be tied up with "carbon capture" – the technology that does not yet exist for removing the carbon dioxide produced by burning coal and storing it somewhere other than in the atmosphere.

This is the first big test of the credibility of Ed Miliband, the new Secretary of State for Energy and Climate Change . There should be no question of Kingsnorth going ahead without an urgent increase in public money pumped into research into carbon capture. Mr Miliband has to ensure that Britain is at the leading edge of this technology. Not just because clean coal could cut Britain's emissions but because carbon capture is a huge global business opportunity.

On both Heathrow and Kingsnorth Mr Brown shows a weakness for the politics of the long grass, inventing conditions that in effect postpone difficult decisions until after the next election. But if Mr Brown really still thinks it worth pretending to press ahead with the third runway, the auguries of his commitment to the green cause are not good.