At the crux of the House of Commons debate on the renewal of the Trident submarine fleet this week, Britain’s new Prime Minister was asked: “Is she personally prepared to authorise a nuclear strike that could kill 100,000 innocent men, women and children?” Theresa May answered “Yes. The whole point of a deterrent is that our enemies need to know that we would be prepared to use it.” There was an intake of breath, for rarely has the policy of nuclear deterrence been so bluntly stated. Yet her answer was consistent with that of every prime minister since Clement Attlee. For nothing else, as she explained, made sense.

And yet in a way it does not. At the point at which she would be authorising a nuclear strike likely to kill “100,000 innocent men, women and children”, deterrence would have failed. Britain itself would be under nuclear attack, or about to be. And the deaths of those innocent people would achieve nothing. There would be no victors. It is unlikely Mrs May would still be around to tell the attackers, “We told you so.” Or that the attackers would be around to hear her.