The current pressure on national spending plans means we have to challenge every government spending decision from fundamental principles. This is particularly true of the big programmes, no matter how politically difficult. One of the obvious, but controversial, big programmes is the proposed Trident upgrade, estimated to cost about £20bn ($33bn, €23bn).

What is the military for?
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Do we need a nuclear deterrent? There is no denying that the world’s political climate has changed in the half century since we became a nuclear power. Our threats are no longer principally from rival large-scale nuclear powers, but from rogue states. They may even be from terrorist groups, against whom retaliation would be an irrelevance.