Because Brexit is not risky enough, apparently, Britain’s Conservative government has decided to embark on another project fraught with potential for failure.

For many years, the country has been arguing furiously about a big expansion of Heathrow. Having once opposed the idea, the Tories say they are now in favour.

Prime Minister Theresa May is right: Heathrow needs another runway. But the Government’s announcement settles nothing. Even now, no sensible person would bet on this expansion ever going ahead.

Puzzled by diminishing growth in the world’s advanced economies? Take a look at the near-impossibility of undertaking large-scale infrastructure investment in a place that is prosperous, crowded and mainly wishing to be left in peace.

By any standards, the Heathrow project would be an enormous undertaking. The initial estimated cost is about $20 billion, more than the eventual cost of Boston’s “Big Dig” highway project — and if building ever starts, that number would surely rise. The environmental impact would be serious, too, with hundreds of thousands of people subjected to more noise, and large tracts of valuable property, including an 11th-century church, either blighted or demolished.

Yet the economic case is clear. Demand for air travel continues to increase and Heathrow is at full capacity — already constraining travel to, from and around Britain. Capacity could be added elsewhere, but the alternatives cannot match Heathrow’s ability to serve as a hub. The most recent report makes a compelling case: if economic growth matters most, build a new runway at Heathrow, and start right away.

It is fair to argue, of course, that growth should not matter most. And it would be hard to quarrel with a prompt decision to, say, protect the environment or property values by adding new capacity at a different airport.

The bigger problem is the protracted inability to make a decision of any kind. More than ten years ago, a previous government declared its intention to start the Heathrow project. In due course, the idea was shelved. May’s government will now face the same difficulties: little enthusiasm in Parliament, endless consultation and planning procedures, legal challenges at every turn. Expanding Heathrow may be the wrong choice, but this approach cannot make any choice.

When it comes to essential infrastructure, the new capacity that Britain and many other advanced economies need most is the capacity to decide. Endlessly arguing about what to do — then doing nothing — is a sure formula for stagnation.