Reports are proliferating that the US is drawing up plans to attack Iran’s emerging nuclear weapons capability. The fear is that Iran would exploit its nuclear prowess to aggressively promote its interests and undermine those of the west. What is more, deterrence might not work; Iran might actually use a nuclear weapon or make it available to terrorists. And an Iranian nuclear programme could lead its neighbours to follow suit, leading to an even more unstable Middle East.

These are the rationales for contemplating a preventive attack. The problem is that the likely costs of carrying out such an attack substantially outweigh probable benefits.