23/07/2013 06:11 BST | Updated 21/09/2013 06:12 BST

Renewing Trident Shouldn't Be Judged on the 'Threat' From North Korea and Iran

Once again renewing Trident is in the news, so some time soon we can expect to hear politicians or commentators explain that Trident is necessary because off the threats from Iran or North Korea, or some other rogue regime. Earlier this year David Cameron said exactly this.

Unfortunately, this is a complete red herring of an argument as long as you've thought about the issue for a couple of minutes. And now I'm going to explain why.

Before we begin - my own view on Trident is that it's unnecessary and the money would be better spent on the NHS, Welfare or forcing the cast of The West Wing to keep making more episodes forever. Even if you don't buy the flower-in-my-hair "nuclear weapons are bad, man" argument that I might want to advance, you can't ignore the fact that our friends over in America have enough nuclear weapons so that if all hell breaks loose, they can probably blow up a few people for us too.

Anyway - this neatly gets me on to my point. When would nuclear weapons be used, anyway? Nukes have a well defined place in their international order, given that they have almost mystical status as world-ending doomsday devices. And so strong is the taboo against using them that realistically they're only ever going to be used in the face of existential threats. That is to say, in response to an attack on us that's so devastating the very existence of the United Kingdom becomes uncertain (though Alex Salmond seems remarkably unfazed by this).

So there is a valid (if not necessarily correct) argument that can be made that we should maintain Trident just in case we end up going to war with Russia or China - y'know, the people who actually have the capability to destroy us.

But what about Iran or North Korea? Imagine waking up one morning and switching on the news to see Seoul is a smoking crater and the Korean People's Army are streaming across the border rapidly advancing across the whole of the country. And for the sake of argument, let's pretend that Britain is still the hegemonic world superpower and not a senile, old, has-been who the young power players still pretend to listen to, out of respect for who he used to be.

Is there going to be a nuclear response from Britain? No.

If anything after an attack like that the nuclear taboo is going to get stronger - seeing the devastation in HD around the world seconds after it has happened is going to be an incredibly powerful thing. Responding to a massacre with a massacre might have worked in the old days of warfare, but morality and sensibilities have moved on. Even in the face of calls for revenge, like after 9/11, the response will be designed to be proportionate and framed in terms of targeting only the bad guys.

Whether successful or not "surgical strikes" and sending in drones to hunt down specific bad-guys in Afghanistan at least have the right intentions - and even the most ardent critic of American foreign policy would admit that this is preferable to a policy of carpet bombing everyone. And it's quite difficult to be precise with a nuclear weapon.

To send in a nuke in response is just going to squander all of the goodwill that South Korea and it's nuclear allies would have in that situation. And I don't know about you, but I can't possibly imagine the US squandering the goodwill it has after an attack by reacting disproportionately.

Seriously though, the response would be a lot like the Korean war - basically every other country teaming up to take on North Korea (and despite Russian and Chinese wielding veto power, it'd be the easiest UN resolution to pass ever). And then there'd be a conventional war where the Korean peninsula is taken back.

The nuclear taboo is too big for us to break over a rogue state using a nuke - if order is to be maintained in the international system, and crucially to retain the norm of nukes being a heinous crime, a nuclear response is not an option. It would be far more dangerous to make nuclear weapons an acceptable tool - "well if Britain or America can use a nuke in response to an attack, why can't we use nuclear weapons to advance our security interests?" they'd cry.

What's also interesting is note before how I explained that nukes would only ever be used if there were an existential threat. If South Korea had nuclear weapons in the above scenario, I wouldn't be surprised if Pyongyang was a radioactive wasteland by mid-morning too, but mercifully only a handful of countries currently have access to nuclear weapons - and however much the South Korean Prime Minister protests following an attack, the US President is going to be a whole lot calmer and rational in responding.

So do we need need Trident? Not to defend against an existential threat from North Korea and Iran that's for sure - and even if they could attack our interests, we wouldn't use nukes to respond even if we had them. So if we're going to have an argument about replacing Trident, can we at least argue in terms of things that are actually real, please?