Dr Julian Lewis: Whether he remains committed to the continuation of the UK's Trident nuclear deterrent after the Vanguard submarines are withdrawn from service.

The Prime Minister: My hon. Friend will be delighted to know that the answer is yes, we are committed to retaining an independent nuclear deterrent based on the Trident missile system. That is why we have continued with the programme to replace the Vanguard-class submarines, including placing initial design contracts with BAE Systems.

Dr Lewis: That is indeed an excellent answer. Given that a part-time nuclear deterrent would be dangerously destabilising, will the Prime Minister confirm that the British Trident successor submarines must and will operate on the basis of continuous at-sea deterrence?

The Prime Minister: My hon. Friend is absolutely right to raise this issue. One of the key elements of the credibility of our deterrent has been that it is continuously at sea, and the Royal Navy takes immense pride in having been able to deliver that without a break over so many years. I have met some of the crews and visited some of the submarines. What they do is incredibly impressive and I pay tribute to them for the service that they provide. Yes, being continuously at sea is a key part of our deterrent.

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[Sir Nick Harvey [Liberal Democrat former Defence Minister]: Returning to the Trident issue, has the Prime Minister looked at the severe cost pressures facing defence at the very moment the Trident replacement has to be paid for? Joint Strike Fighter airplanes, Type 26 frigates, unmanned aircraft and Army vehicles all need paying for at much the same time. This has to come out of the defence budget, and austerity will be with us for some time yet, so will he keep an open mind about how exactly to replace our nuclear deterrent?

The Prime Minister: All the things that my hon. Friend lists are programmes that are fully funded and will be properly invested in, because, as he well knows – because he played a major role in it – the Government have sorted out the defence budget. Having carefully considered the issue of the nuclear deterrent, I do not believe that we would save money by adopting an alternative nuclear deterrent posture. Also, if we are to have a nuclear deterrent, it makes sense to ensure we have something that is credible and believable, otherwise there is no point in having one at all.]