Dr Julian Lewis: It cost the Ministry of Defence £1.4 billion to extend the life of the four Trident submarines so that the Liberal Democrats could study alternatives. Now that that study has shown there is no alternative to Trident, will the Prime Minister consider signing the main-gate contract for the first two submarines, so that we can never again be blackmailed by the Liberal Democrats in a hung Parliament?

[The Prime Minister: I have to credit my hon. Friend with remarkable consistency on this issue, on which, basically, I agree: we have Trident, it is the right approach and we need to renew Trident. Actually, the delay of the main-gate decision has saved us money, rather than cost us money. His point about the review is absolutely right. It shows that if we want a proper functioning deterrent, we need to have the best, and that means a permanently at-sea submarine-based alternative. That is what a Conservative-only Government, after the next election, will deliver.]