Britain's nuclear arsenal: There is no alternative THREE years ago the Liberal Democrats demanded a review of Britain's nuclear weapons system as a condition of joining a coalition government. Their Tory partners were committed to replacing the four Trafalgar-class Trident ballistic missile submarines that have been on patrol since 1994 with a similar system when the current boats reach the end of their operational life, at a cost of about £20 billion ($31 billion). A decision must be taken by 2016. The Lib Dems have now got their review. It does not flatter them. For years the Lib Dems have insisted that Britain should have a cheaper, less powerful nuclear deterrent. They argued that nuclear-armed cruise missiles carried on adapted attack submarines would cost less and show that Britain was moving away from "outdated cold war thinking." This must have seemed shrewd politically. It differentiated them from the other two parties and kept their own large pacifist wing quiet, without attracting the "ban the bomb" label that hurt Labour in the 1980s. The Cabinet Office's 64-page review, delivered this week, painstakingly examines the implications and costs of all the alternatives to sticking with Trident. Its findings are both entirely predictable and extremely embarrassing for Nick Clegg, the Lib Dems" leader, and for Danny Alexander, the chief secretary to the Treasury. Options such as cruise missiles launched from carrier-borne aircraft or a land-based ballistic missile system are quickly dismissed because of their vulnerability to pre-emptive attack. But the idea of converting some of Britain's new Astute-class attack submarines to carry nuclear cruise missiles also fails to stand up. There would be little if any saving in the number of submarines required compared with the planned seven Astutes and four Vanguard ballistic missile boats. In practice, "dual purpose" submarines would not be able to mix different types of patrol. They would also be more vulnerable than ballistic missile boats because the shorter range of cruise missiles would mean they would have to operate closer to an enemy's shore line. And the cost of designing either a stealthy or supersonic cruise missile and the warheads to go with them would hugely exceed the Trident D5 missiles which already exist. The Lib Dem's "cheaper" alternative would cost about 45% more than current plans and be far less effective. Moreover, it could almost certainly not be built in time. Snubbed, Mr Alexander tried another tack this week. Instead of four new Trident boats, the Lib Dems would go for only two or, at most, three even if it meant sacrificing the guarantee of having one boat on patrol at all times - "continuous at-sea deterrence," as it is known. Yet this substantially weaker deterrent would save only about £56m a year during the 30-year life of the programme - about 0.17% of the overall defence budget. Mr Alexander thinks that given the nature of the threats he predicts Britain will face between now and 2060 that would be a saving worth having. Others, recalling that it is only 22 years since the cold war ended, and less confident that they know what the future will look like, may feel that keeping up with the old insurance premium is a lot less risky.