THE answer is yes. The leader of the Lib Dems Jo Swinson would be prepared to use nuclear weapons. She would be willing to push the button. She would take the ultimate decision if she had to. Everyone got that? She would do it. No doubts. No hesitation. Yes.

But what did she mean by “yes” exactly? The critics said it showed Ms Swinson was willing to sanction Armageddon. “Not even a moment’s hesitation about the prospect of killing millions of people,” said CND. “It’s sickening to hear this question asked and answered as if it’s some kind of virility test,” said Nicola Sturgeon. The consequences should be made clear, she said.

But who on earth isn’t aware of the consequences of using nuclear weapons? The dread of nuclear conflict has been deep in the British psyche since the Second World War, and even more so since the Cold War. We can see the mushroom clouds in our minds and we can hear the government information films: "when the attack warning sounds, you and your family must take cover at once; no place in the UK will be safe; cover any dead bodies with polythene or sheets".

READ MORE: Nicola Sturgeon slams Jo Swinson for 'disgraceful response' to nuclear weapons question

Jo Swinson is a child of the 80s and will have seen those images and heard those warnings like everyone else, but when she said yes to using nuclear weapons, she wasn’t saying yes to bringing about mass destruction and it’s absurd to say she was. She was saying yes as part of the political, diplomatic and military construct that surrounds the nuclear deterrent. She was saying yes to ensure a no – no to ever having to start a nuclear war.

The submariner Richard Humphreys explains it well in his new book Under Pressure, which is a brilliant account of what it’s like to work on nuclear submarines and live with an awareness of what they can do. Humphreys says he knew that at any point the sub was potentially just 15 minutes from the start of an apocalypse – 15 minutes is how long it takes between receiving the firing signal from the PM and the nuclear warheads being launched.

But Richard Humphreys also knew the differences between the theory and the reality. On every nuclear sub, there is a sealed letter from the PM telling the captain what to do in the event of a nuclear attack on Britain. The options are: do nothing; leave it to the captain; put the boat under the control of an ally; try to save the sub by going to another part of the world; or the nuclear option: retaliate with the warheads. In other words, the weapons would only ever be used as a second-strike option.

READ MORE: Nicola Sturgeon confirms she would not use nuclear weapons 

The important point, and the difference between the theory and the reality, is that if we ended up in those circumstances, the deterrent would have failed; it would have proved worthless. But it hasn’t. Humphreys and his comrades lived, ate, slept, and worked 100ft from the world’s most powerful weapon while also believing whole-heartedly that they would never receive the firing signal. Who was going to take the decision to destroy their own country? The threat of a counter-attack was real, therefore the possibility of an attack was almost non-existent.

All of the British armed forces is based on this peace-keeping premise – nuclear and non-nuclear. When the first of the Astute class of submarines arrived at Faslane, I was in a boat that accompanied her up the Clyde and the military personnel told me what the sub could do. Astute can carry more missiles than any previous class of submarine and has 50% more firepower than the Trafalgar class, but the point isn’t to use weapons, the point is to prevent others from doing so. Astute and the other submarines of her class will mainly be engaged on anti-submarine work and intelligence – deterrence in other words.

It is in this context that Jo Swinson’s response to the question about nuclear weapons has to be seen. She wasn’t saying yes to killing millions of people – of course she wasn’t – she was saying yes to maintaining the deterrent effect that submariners like Richard Humphreys feel close-up 300ft under water. The moment you say no, as Jeremy Corbyn and Nicola Sturgeon do, the deterrent effect no longer works, so you have to say yes on the basis of a conviction that the weapons will never be used – indeed you are saying yes to ensure they never are.

Despite the protests about the millions of people she was apparently prepared to kill, this is what Jo Swinson was doing when she said yes. Her answer does not exclude multilateral disarmament – indeed, safe disarmament should be the aim of every British government. It also does not mean you are prepared to kill millions of people. It means the opposite: it means you want to prevent the deaths of millions in a world where some states have nuclear weapons and show no signs of abandoning them.

So do not castigate Jo Swinson for saying yes to the question about nuclear weapons. Acknowledge that, in a mad, mad world, she had no choice.