A deterrent is useless if no one thinks it will ever be used. The only conceivable use of Britain’s nuclear deterrent would be in the event of a nuclear attack on the UK, and if that has happened then there is little point in firing the missiles as there will be nothing left to save. Any blackmail today is likely to be much smaller, no state is going to threaten the use of nuclear weapons in order to get their way on trade. The only real possibility of nuclear blackmail is by terrorists who could not be deterred by a nuclear armament.