Several years ago I was at a party, I think it was in South Kensington.

I remember there being lots of tweed and corduroy, and some of those wearing it worked for defence think tanks. I'm a great believer in trying to glean something from those with expertise beyond my ken, so I questioned one about the UK's nuclear deterrent.

Until this point it wasn't something I'd given a great deal of thought, certainly not beyond buying (rather lazily) into the orthodox line that Trident was a necessary evil.

Nevertheless I played devil's advocate, and asked this person what the main argument was in favour of an "independent" nuclear deterrent. Oh, he replied (looking a little surprised someone might require an argument), "it's all about maintaining a seat on the UN Security Council."

I then asked what I thought was an obvious follow-up question: "And why is retaining that important?" Again, this was greeted with polite bafflement and what I considered a rather insubstantial response. After much pussyfooting around, it apparently boiled down to something called "prestige".

Now these days I'm regarded as rather eccentric for continuing to believe that the UK and its associated brand of "Britishness" still counts for something in the world. This impression is confirmed whenever I travel and talk to people about where I'm from; it still resonates, indeed arguably more so abroad than at home.

Nuclear weapons have never once featured in those conversations, and although that's an anecdotal observation I nevertheless struggle to believe that Trident is somehow integral to British "standing". Indeed, a few years ago I spoke to another security specialist who believed that even without it the UK would retain its permanent membership. Reconstituting the Security Council, she argued, was a Pandora's box its other members would be reluctant to open.

Late last week I took part in a seminar at Christ Church College, Oxford, entitled "Justifying Trident?" that considered the moral, political and economic arguments for the UK's nuclear deterrent, and although most of those taking part were broadly pro, they had much better arguments than my be-Tweeded friend in South Kensington.

A dissenting voice came from someone who, in any other context, would have been perceived a pillar of the military establishment, former Deputy Commander-in-Chief UK Land Forces General Sir Hugh Beach. A Wykehamist and graduate of Edinburgh University, he referred to himself as a "sacrificial lamb", but in fact set out what was to my mind a lucid and persuasive argument against Trident.

If, as successive UK governments maintain, there exist nuclear states that might "pose a grave threat to our vital interests", then, argued Sir Hugh, one is entitled to ask what, when and where? "No other area of military procurement", he added, "is justified on the basis of a general insurance against the unforeseen." As another speaker at the seminar put it, if the best argument for Trident was some unidentified future threat then it was toast intellectually. Any justification, he added, had to hinge upon the word "deterrence".

But that too is problematic, for as Sir Hugh observed, it's actually quite hard to demonstrate the UK has "prevented action by any other country that she could not otherwise have prevented by virtue of her nuclear arsenal". The pretence, meanwhile, that the British deterrent is "independent" is precisely that, a pretence, and it's not clear under what scenario the UK wouldn't be able to count upon NATO or US support if it faced an external threat.

But my main objection is the cost. As Sir Hugh put it at the seminar, the perceived benefits of Trident hardly outweigh the vast expense of renewing and maintaining it. In good economic times this would be true, but in the context of unprecedented austerity (which include hefty reductions in defence expenditure), it is close to unanswerable.

Cleverly, the First Minister has recently been making precisely this point, although for Nicola Sturgeon the financial argument plays second fiddle to her moral opposition. Although there is certainly a moral case against Trident, I've never been convinced that morality and politics mix: it's too subjective, and can too easily be subverted in unpleasant ways.

Idealism also isn't helpful: both isms - multilateral and unilateral - fall into this category, although at least the former has some identifiable achievements to its name. As the late Margaret Thatcher once said: "You cannot dis-invent the nuclear weapon, any more than you can dis-invent dynamite." Nevertheless, politicians (mainly Labour and Tory) struggle to break out of their obsession with "prestige".

Take Tony Blair. As he reflected in his memoirs, although as Prime Minister he could see the "force of the common sense and practical argument against Trident", giving it up would have been "too big a downgrading of our status as a nation", as if that "downgrading" hadn't already occurred. Indeed, Labour in particular has always struggled on defence: perceived as "weak" by the electorate, it overcompensates by trying to be "tough", and, of course, being pro-Trident is one (expensive) way of doing so.

When it comes to public opinion, however, the largest proportion of Scots are actually closer to Jim Murphy's multi-lateralist position. The SNP has spent years referring to "a long-standing national consensus" against Trident, but when Lord Ashcroft probed public opinion almost two years ago the results were surprising. Not only did more Scots want Trident to stay (43 per cent) than go (39 per cent), a majority supported either a like-for-like replacement (20 per cent) or a cheaper nuclear alternative (31 per cent). So Scotland is not, as the SNP likes to depict it, one giant branch of the CND.

The SNP's "red line" on Trident is also beginning to undermine its broader "vote SNP get Labour" election pitch. Yesterday Alex Salmond told the BBC's Andrew Marr that supporting Labour on an "issue-by-issue" basis would be a means of the SNP agreeing to disagree with Ed Miliband on Trident renewal while supporting him more broadly. But if that is so then not only is it not a "red line", but I don't see how the SNP could support either a Labour-sponsored Queen's Speech or Budget, for both would need to include provision for Trident, and without those a minority Labour administration would be toast.

Beyond electoral positioning (and that's what most of the above is), however, if opposition to Trident defines your political world view (and it doesn't mine), then supporting independence makes perfect sense: removal won't be cheap, easy or geopolitically cost-free but it would happen - eventually - and under the constitutional status quo that prospect is markedly slimmer.

As for the US response if the UK scrapped Trident (not happy bunnies), Sir Hugh Beach suggests justifying it on the basis that we would be better able to support Washington in "areas where things actually happen", i.e. beefing up conventional forces. It's a good, pragmatic argument, and certainly more compelling than the contrary case.