It has three parts - submarines, missiles and warheads, and although each component has years of use left, they cannot last indefinitely.

BBC: Labour 'open' to cheaper Trident alternatives

Because handedness has a genetic component the researchers wondered why the proportion of left-handers should have remained so constant over 30, 000 years - the age of the oldest cave studied.

BBC: Cave handprint, Montpellier University

The notion that defense, the biggest component of discretionary outlays in the budget, can be left untouched by this process is naive.

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