Dr Julian Lewis: Thank you very much, Madam Deputy Speaker, for permission to speak in this debate. I apologise to the House for the fact that because I was chairing a public sitting of the Defence Committee I could not be here for the opening speeches. For that reason, too, I have deliberately refrained from making any interventions.

Although the issue of strategic nuclear deterrence is very divisive, we can all agree that the calibre of the speeches on both sides of the House – and on both sides of the argument – has been very high indeed. If the Chairman of the Defence Committee had to mirror the views of its members, I would probably spend just over 90% of my time arguing passionately in favour of the nuclear deterrent and just under 10% of it arguing equally passionately against it, because we have, and are delighted to have, on the Committee the hon. Member for Dunfermline and West Fife (Douglas Chapman), who is a consistent and thoughtful opponent of Trident.

Fortunately, however, I do not have to mirror those views. The views I am expected to put forward are clearly marked as my own, and they have been pretty much the same for 35 years, half of them outside this House and the remainder inside this House. On my having been elected to chair the Defence Committee, something may have come as a bit of a surprise to people who looked at the list of the five hon. Members from the Labour Opposition who were kind enough to nominate me to that role.

One was the Shadow Armed Forces Minister, the hon. Member for North Durham (Kevan Jones), and that is hardly a surprise. However, at the other end of the spectrum, I was fortunate enough to enjoy the support of the current Leader of the Opposition [Jeremy Corbyn]. The reason was that we both agree on one thing. Even though our views on whether we should continue to have a nuclear deterrent are diametrically opposed, we both agree that both sides of the case have a good argument to make, and that when we make it on the Floor of the House, everybody learns something.

With the support of the now Leader of the Opposition, I managed to secure, on 17 January 2013, the first full debate on the whole issue of Trident and deterrence in the main Chamber since the vote on 14 March 2007 when the initial gate was approved. Anybody who really wants to see both sides of the intellectual argument at their best could do no better than to get a copy of that debate, from which I shall repeat my five main military arguments.

I fear that I will not have enough time to deal with the point about cyber-vulnerability, so I commend to the House the article in the Guardian today in which Franklin Miller, a leading expert for 20 years on the American nuclear systems and, indeed, the holder of an honorary knighthood from this country, explains why there is no question of the nuclear deterrent being connected in any way to the internet and being in any way vulnerable in that regard. Similarly, on the question of Tiers, I merely say that Tier 2 threats are often more dangerous than Tier 1 threats, and that is why the Defence Committee has just published a report in which we challenge the utility of ranking threats in this way.

Let me now stick to reciting my few arguments. There is not much time for any detail unless someone is kind enough to intervene on me. The first of the military arguments is the most important of all: that future military threats and conflicts will be no more predictable than those that engulfed us throughout the 20th century. That is the overriding justification for preserving armed forces in peacetime as a national insurance policy.

Mrs Sheryll Murray: Does my right hon. Friend agree that deterrence is probably our best defence?

Dr Lewis: That point leads directly to the question of what it means to say that we are “using” Trident. Those of us who believe that the possession of a deadly weapon is the best method of stopping other people who possess similar deadly weapons from using them against us, say that Trident is in use every day of the week, and if ever the button had to be pressed, it would have totally failed in its purpose.

My second argument is that it is not the weapons themselves that we have to fear but the nature of the regimes that possess them. Whereas democracies are generally reluctant to use nuclear weapons against non-nuclear dictatorships – although they did against Japan in 1945 – the reverse is not true. Let us consider what might have happened if in 1982 a non-nuclear Britain had been facing an Argentina in possession of even just a few tactical nuclear bombs and the means of delivering them. Would we then have dared to use our conventional forces against its inferior conventional forces?

The third argument is that the United Kingdom has traditionally played a more important and decisive role in preserving freedom than other medium-sized democracies have been able, or willing, to do. Democratic countries without nuclear weapons have little choice but either to declare themselves neutral and hope for the best or to rely on the nuclear umbrella of their powerful allies. We are a nuclear power already, and it is also much harder to defeat us by conventional means because of the existence of the English Channel.

The fourth argument is that because the United States is our closest ally, if the continent of Europe were ever occupied and the nuclear forces of the United States had not been used, an enemy might feel that they could attack us with nuclear weapons with impunity.

Alec Shelbrooke: For those who say that our nuclear deterrent is in the hands of the Americans, what does my right hon. Friend make of the fact that every Prime Minister has to write a letter held in every submarine that is never, ever seen unless in the most dire circumstances?

Dr Lewis: My hon. Friend is exactly right. There is no question but that the Trident nuclear system is entirely autonomous. Indeed, nothing – not the Americans, not any form of cyber-bug – can possibly intervene if, heaven forbid, the worst happened, the United Kingdom were attacked in part or in whole and the submarine commander had to open the dreaded letter written by the Prime Minister.

The fifth and final military argument is the most important of all. I put this to people when they try to say: "Well, you’re inflicting cuts on our conventional capability". The argument is that there is no quantity of conventional forces that can compensate for the military disadvantage that faces a non-nuclear country in a war against a nuclear-armed enemy. The atomic bombing of Japan is a perfect example, not only because the Emperor was forced to surrender, but because what of might have happened under the reverse scenario: if Japan had developed atomic bombs in the summer of 1945 and the allies had not, a conventional allied invasion to end the war would have been out of the question.

The debate should and will go on, and I congratulate SNP Members on giving us the opportunity to take part in it today.

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SNP MOTION: That this House believes that Trident should not be renewed.

VOTE: The House having divided: Ayes 64, Noes 330 ... Question accordingly negatived.

[NOTE: The Labour Party were instructed to abstain, but 6 Labour MPs voted for the Motion, and 14 against]