NICK Clegg, the Deputy Prime Minister, tells us that "the decision on the Trident replacement will not be taken until 2016, however much other people may not like it that way".

Mr Clegg wants us to believe him, too. The Coalition Agreement, he insists, is "crystal clear".

Sadly for him, one of Mr Clegg's partners in that deal detects no such clarity. Philip Hammond, the Defence Secretary, is busy making a down payment of £350 million, part of a planned expenditure of £3 billion for mere "preparatory" work on the project, just to prove his esteemed colleague wrong. Mr Hammond is, if you like, putting our money where his mouth is.

He doesn't stop there. Repeating the Ministry of Defence's ritual claim that there are no plans to move Trident boats from Scotland – does that also count as preparedness? – Mr Hammond makes a further bet against Scottish independence. Behind his optimism is a challenge: and what does the SNP mean to do about that?

As a glimpse into the nature of power in Britain, all of this is fascinating. Mr Hammond is perfectly happy, for one thing, to make a fool of Mr Clegg and his search for Trident "alternatives". Complacently, the Minister further assumes that the thermo-nuclear binge will go on even if Labour wins the next British General Election. Why else spend all that money? Where nukes are concerned, coalitions, like changes in government, count for nothing.

Finally, there is an implicit threat. It amounts to this: even if the SNP take power in an independent Scotland, the Royal Navy will refuse to budge from the Clyde. There are no plans for an alternative Trident base. There is certainly no appetite to replace Coulport's gigantic "explosive handling jetty". That was priced, conservatively, at £2 billion all of 20 years ago.

Is Mr Clegg being taken for a fool, or is he putting on an act? Is Ed Miliband's Labour Party being taken for granted over its likely attitude towards a useless, immoral extravagance? Does Mr Hammond have reason to believe that the SNP can be browbeaten even if Scotland votes for independence in 2014? There, regardless of rhetorical questions, goes another £350 million.

Of all the queries, the one asked of Scottish nationalism is profound. Having assumed the moral high ground for so long, it lost altitude, and more than somewhat, in its conference vote on Nato. The party leadership can finesse a reprehensible choice all it likes. A loyal alliance with nuclear-armed friends, a successor UK among them, means co-operation with those friends. At best, to adopt the parlance of another trade, you are enabling the addict.

What does the SNP intend? It is specious to invoke all the Nato countries that never got around to acquiring nuclear weapons. Those states did not enter the alliance with strategic assets to match Faslane-Coulport. They did not subvert good faith, as Whitehall and the Pentagon define the term, by obstructing the designs of their partners. Nato makes no bones about its core purpose. It will retain nuclear weapons for as long as such devices exist on the planet. There is no clause that says, "if that's OK with Scotland".

The SNP has one fact in its favour, nevertheless. For now, at least, there is nothing that a Scottish Government can do, or attempt to do, about Trident beyond accusing Mr Hammond of dumping his WMD on this country. Mr Clegg's situation is different.

His precious Coalition Agreement is supposed to be binding. It contains a provision for a study, based in the Cabinet Office but led by members of Mr Clegg's party, of alternatives to Trident replacement. A report is due in January. But the world can see that Mr Hammond is simply ignoring this supposed deal. He is having a £350 million laugh, confident that the LibDems will fume but do nothing to put the Coalition at risk.

Mr Clegg could stop the folly. Instead, he merely accuses Mr Hammond of "jumping the gun". The deterrent threat facing the LibDems in this case, after all, is the loss of office and a General Election. Mr Clegg does not have the stomach for that fight. The Tories are committed, as Mr Hammond said recently, "to maintaining a continuous deterrent, based on the Trident missile" and they do not propose to be hindered by the hired help. Yet again, the Coalition Agreement is shown to be worthless.

So where is Labour in all of this? Mr Miliband, at least a dozen points ahead in the polls, could threaten to cancel Mr Hammond's schemes on any number of grounds. The Tories say the country is broke, yet they want to spend £80 billion, by one estimate, on a system that can never be used? How does that contribute to non-proliferation, never mind disarmament? How does it better defend Britain when terrorism is held to be the existential threat of the 21st century?

These arguments have been rehearsed time and again, not least in Scotland. Mr Miliband could add to them easily enough. The Tory plan to cap child benefit by curbing procreation among the poor might save £200 million a year. Mr Hammond is meanwhile blowing £3 billion just in case Trident is to be replaced, or so he says. Any Labour leader should be able to make something of that contrast. The present leader ponders silently.

As things stand, a minority party abetted by one section of the military-industrial complex is making major decisions unhindered. The Army, cut to the bone, is not demanding the replacement of Trident. The RAF has no desire to see the Navy given a new, strategically useless toy. A free vote among Labour and LibDem MPs would find no support for Mr Hammond's schemes. The SNP might be self-contradictory where Nato is concerned, meanwhile, but the opposition to nukes remains wholehearted and real.

Some real political deterrence is required. If the LibDems won't act and Labour will not speak, it falls to the Nationalists to spell out when and by what means the Trident boats would be expelled from Scotland. The first step will be to admit that the task is not as simple as it sounds.