The tale of the Trident system's renewal is fast becoming another parable of Coalition politics.

The Liberal Democrats are deeply unhappy with the plans. No "final decision" is supposed to be made until after the next General Election. Yet the Ministry of Defence and the Tories are carrying on regardless.

The LibDems see no need, strategic or economic, for "like for like" replacements for the boats, warheads and missiles. As though fighting the good fight in a parallel universe, they are busily examining alternatives. Meanwhile, Defence Secretary Philip Hammond was yesterday announcing £350 million in Trident design contracts.

Is that how defence spending is supposed to happen in straitened times? What becomes of the £350m earmarked for BAE Systems, Babcock and Rolls-Royce if the "final decision" happens to go in the LibDems' favour? Shareholders in those firms probably know the answer.

In fact, Mr Hammond has £3 billion to spend on Trident design work while he plans to scrap regiments and reduce the army to its smallest size since the Boer war. That sum was set aside a year ago – perhaps as a tribute to a thriving British economy – by the then Defence Secretary, Liam Fox. His decision, in turn, followed the spending since 2007 of £900m on submarine design. That was Labour's largesse.

We are in the realm of the sort of tidy sums familiar to the MoD. The LibDem review – strictly speaking, the Coalition's review – is being carried out by Nick Harvey, the Armed Forces Minister. He has, as they say, a range of options. One involves smaller missiles being carried on existing Astute-class attack submarines. If Mr Harvey won the day, could we expect a refund for the wasted design effort?

Before anyone mentions the moral or military arguments against Trident, a typical defence establishment ploy is worth noting. In the name of planning and preparedness, the MoD spends vast sums. When objections are raised, the ministry retorts that it's too late, that the cost of cancellation would be disgracefully wasteful. The neat trick was attempted, you'll recall, in the argument over Gordon Brown's aircraft carriers.

The LibDems might be expected to understand this, and some do understand. Menzies Campbell, for one, argued in a patently sane article the other day that the ability to annihilate Moscow should no longer be a central defence policy for a modern British government. But the Tories and the military-industrial complex pay no mind to Nick Clegg's quibbling party.

The attitude seems to be that they have already cut the planned stockpile of warheads for the four new boats – from 225 to 160 – and reduced the number of missiles that each submarine will carry from 12 to eight. Won't that persuade the world's dictators that Britain leads the way on disarmament? Besides, as they remind us repeatedly, the cost of replacing the nuclear fleet will be a mere £25bn.

If you can name a long-term MoD procurement project that has come in on budget, you are welcome to believe it. This year's estimate is already double the figure suggested when Tony Blair decided in 2006 that he could not live without nukes. It also overlooks details that seem to be beneath the MoD, details such as VAT.

A nuclear capability is certain of other costs. Some of these are fascinating, but never mentioned when the figures quoted are restricted to "design and build". Just over a week ago, for example, the MoD announced that it would be continuing to invest £1bn a year in the Atomic Weapons Establishment (AWE) in Berkshire.

The contract is expected to run for five years. The MoD's press release makes it clear, however, that the deal has nothing to do with new nukes. In fact, the "agreement does not relate to any replacement warhead programme". Instead, reflecting what is undoubtedly the real timescale, the "investment will enable AWE to perform its vital work in support of the UK's nuclear deterrent until March, 2018, when another priced period of work will be agreed".

It is worth observing, meanwhile, that AWE – Aldermaston and Burghfield – long ago ceased to be an outpost of HMG and quaint boffins. Since 2000, the establishment has been managed and operated by AWE Management Limited (AWEML). AWEML is a consortium formed by Jacobs Engineering, Lockheed Martin UK and Serco.

The first of those companies has its headquarters in Pasadena, California. The second is a wholly owned subsidiary of the huge American defence contractor. The third partner is proudly British, and the proud holder of Government contracts for everything from privatised prisons to electronic tagging, "immigration removal centres" and the maintenance of Britain's ballistic missile early warning system.

Forget then, that no-one can name the enemy liable to be deterred or destroyed by Trident. Forget what Britain can and cannot currently afford. Forget to ask whether the sums involved are the best use possible for a restricted defence budget. Is it truly the role of the MoD to hand the management of nuclear defence, not to mention whatever state secrets and billions we have left, to foreign interests?

One potential cost of Trident renewal is never mentioned. What happens if Alex Salmond wins his independence referendum and an SNP Government in due course keeps its promise to expel the nuclear boats from Faslane? London's policy is to have no policy.

Peter Luff, Minister for Defence Equipment, said in a written answer in January: "The Ministry of Defence is not making plans to change the base ports of those classes of submarines currently base-ported at Her Majesty's Naval Base Clyde. The department does not therefore hold cost estimates or other information that would relate to such changes." The Government, Mr Luff said, was "confident" of Scotland's support for the Union.

The reality is that no alternative base can be identified that does not involve incalculable expenditure and an uproar in the south. If you happen to believe that Trident is an issue of morality as well as money, this might colour your attitude towards the referendum. Vote Yes, as the SNP probably won't say, for Britain's sake.