Dr Julian Lewis: I am grateful to the Chief Secretary for giving way. He says this is the most comprehensive examination for many years – that is open to question – but will he explain why it considered only the four-boat and three-boat options for Trident, not the two-boat options that the Liberal Democrats plan to put to their conference as Liberal Democrat policy?

The Chief Secretary to the Treasury (Danny Alexander): My hon. Friend will have a chance to see the proposed Liberal Democrat policy paper when it is published in a few weeks’ time. The purpose of this debate is to consider the Trident alternatives review.

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Mr Kevan Jones: ... There was another option that was deemed unworthy of examination by what is otherwise a thorough and forensic document: sending two unarmed submarines out on patrol with the intention of stepping up our posture in a time of crisis. That is the policy the Chief Secretary has just proposed.

Dr Lewis: I read that report in The Times, and it seems to me that what was being said was that the Labour Party is committed to continuous-at-sea deterrence and the only question is whether it can do it with three submarines or whether it would have to do it with four. The one thing that is absolutely certain from the report is that it cannot be done with two, yet the Chief Secretary’s position is that if a crisis arose they would step up their performance. How could we build a third or fourth extra submarine in time to step up our performance if a crisis arose?

Mr Jones: I know that the hon. Gentleman has studied this subject thoroughly and is an expert. I totally agree with him. As I said, the Chief Secretary clearly has not read his own report because, as the hon. Gentleman rightly says, it outlines the problem with having only two submarines.

The Liberal Democrats briefed the newspapers earlier this week that the two-boat option would be a way forward, and the Chief Secretary has just re-outlined that ludicrous policy. My right hon. Friend the Member for East Renfrewshire (Mr Murphy) hit the nail on the head yesterday when he said that it was a little like installing a very expensive burglar alarm on one’s house with no batteries and putting up a sign saying, "Burglars, come in." The only difference is that this would be a multi-billion pound deterrent that would not deter.

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Dr Lewis: For the sake of clarity, it is important to stress that in the report the only options for Trident are a four-boat fleet or a three-boat fleet. That is where the £4 billion would come into it. The report does not even consider or cost a two-boat fleet, because it would be impossible to reinstate to a higher level of readiness.

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Sir Nick Harvey: ... To answer the points made by my right hon. Friend the former Defence Secretary [Liam Fox], I am not saying that it might not be necessary in the future to crank up to a more rigorous posture – it might well be – but I do not see how anyone can rationally argue that we have to do that at the moment. The idea that the nuclear capability has a deterrent effect at all only by being patrolled 24/7 is clearly absurd. All the rest of our capability has a deterrent effect against a variety of aggressors in a variety of scenarios and we do not see the need to exercise any of it on a 24/7 basis.

Dr Lewis: I could just about stay with the hon. Gentleman’s argument if he was saying that we ought to build four submarines but not send them all to sea until the situation became worse, but he is not saying that. He is saying that we should build only two or three such submarines, which would mean if the situation got worse, we would not be able to reinstate continuous-at-sea deterrence because we would not have the submarines. Without the submarines, we cannot have the posture, much as he might like to reinstate it when the situation gets worse.

Sir Nick Harvey: I can agree to the extent that we must ensure that we build enough capability that we can mount the deterrent we will need at the point that we need it. What that will comprise is a matter for further debate and further study and I note with interest that even those on the Labour Front Bench and the former Defence Secretary, the right hon. Member for Coventry North East (Mr Ainsworth), acknowledge that it remains to be seen whether we need four or three to do that.

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Dr Lewis: The hon. Gentleman [John Woodcock] may be aware that all the talk about the Liberal Democrat conference considering a two-boat option comes from a Liberal Democrat document that has been drawn up by a Liberal Democrat group. When I asked the Chief Secretary earlier today at a briefing whether any copy of the review was going to be taken to the Liberal Democrat conference for consideration, he said

"Well, I might take a copy, but it will just be in my briefcase."

In other words, the review is not the document that the Liberal Democrats are going to consider. They are going to consider a completely different document making completely different recommendations, which the review did not even bother to consider.

John Woodcock: The hon. Gentleman is right. If we were living through a Monty Python sketch, this would be the point when the army major intervenes and says that this is all getting too silly and we have to stop it at once. But of course the consequences for the nation’s security, and the 13,000 people directly employed in Barrow and across the UK, would be bitterly serious if the Liberal Democrats had their way on their part-time deterrent idea. That is why it would be a very good thing if this shambolic process now sinks without trace. Even their own document makes it clear just how hopeless an alternative a part-time deterrent would be. It states that

"a 3-boat fleet would risk multiple unplanned breaks in continuous covert patrolling as well as requiring regular planned breaks for maintenance and/or training."

They are effectively suggesting that we pay billions for something that we cannot be sure will be available to do the deterring when needed. ...

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Jeremy Corbyn: I am pleased we are having this debate and that the hon. Member for New Forest East (Dr Lewis) has spoken, because he sincerely believes in nuclear weapons as much as I sincerely disbelieve in them. ... The review that the Liberal Democrats have asked for and that was no doubt produced at enormous expense is not a discussion of the alternatives. It is a discussion of weaponry and, in part, of perceptions of security and risk, but it is not a discussion of the alternative to Trident and nuclear weapons, which is not to have them at all and instead to aspire to a nuclear-free world. Interestingly, when those who support nuclear weapons are challenged, they all say they want to live in a nuclear-free world –

Dr Lewis indicated dissent.

Mr Corbyn: Not all of them. I beg the hon. Gentleman’s pardon. I exempt him from my last remark. He wants to live in a nuclear world, but many who agree with him about the decision on Trident want to live in a nuclear-free world, yet they go on to say that they cannot do anything about it, because now is not the time to do it, and then they head off rapidly down the road of weaponry and cold war attitudes towards deterrence and defence. ...

[For Julian's speech in this debate click here]