Shortly after a now-retired (but then active) senior general criticised our involvement in Iraq (which I rejoiced over) I ran into an old acquaintance , a very senior former diplomat, who was spitting teeth and blood over the general’s performance. The man was a complete fool to step so far outside his own responsibilities. It didn’t matter what he had said (the diplomat was inclined to agree with him). Generals just didn’t make political statements in a law-governed country run by the Queen in Parliament, and that was that.

Chastened, I realized I’d been guilty of one of the great sins of politics – forgetting principles for a temporary advantage.

So I moderated my sympathy for the general (who later turned out to be a bit of a disappointment in other ways). In the end, constitutional rectitude was more important than hearing something you agreed with from an important person, especially from a senior soldier.

There’s an argument for saying that this country last underwent a major military intervention in politics in 1688, when John Churchill, the future Duke of Marlborough rather trickily helped Dutch William remove James II from the throne. Then there was the so-called Curragh Mutiny against the Liberals’ Irish Home Rule policy (which was quite serious) , and there were various wild mutterings during Harold Wilson’s years, but I don’t think these can be taken seriously.

So when General Sir Nicholas Houghton, head of the Armed Forces, Chief of the Defence Staff, appeared on TV on the Andrew Marr programme on Sunday ( a transcript can be found here http://news.bbc.co.uk/1/shared/bsp/hi/pdfs/08111503.pdf ), I must admit I wasn’t sure he should be there at all. This is a programme on which politicians are interviewed. The general isn’t one. Very important questions arise. Does anyone know the answers? What was he doing there? Who had authorised him, if anyone? Had he consulted with Ministers or other officers before agreeing to do this? Whose idea was it? Is there a precedent?

Sir Nicholas is, ultimately, the employee and subordinate of the Queen in Parliament. There are other countries where this does not apply, but that is their problem. Here, it is so. The government decides what he must do and what policy he must follow. If he does not like it, he can protest to ministers, up to the Prime Minister, to whom he has access. And if they ignore him, he can either do as they say, or resign.

That’s it, and that’s as it should be. As for his private politics and beliefs, he may be, if he so wishes, a nudist, a vegetarian or a Warmist, a socialist or a liberal or a conservative. It would be interesting to see if he could, even in private, be a Muslim or a UKIP member in practice. I can see either causing difficulties. . He couldn’t be a pacifist because it would make it impossible for him to do his job. By the way, id not think Jeremy Corbyn, who will feature in this post later, is an actual pacifist, just a man very reluctant to support war (as I am). If I am wrong, I should be grateful for chapter and verse.

The general (though he isn't) might well be an opponent of the replacement of Britain’s (to my mind ridiculous, unusable and absurdly large) Trident nuclear ‘deterrent’. I qualify the word ‘deterrent’ because for some years I have been unable to answer the question ‘Who or what does Trident actually deter, who is a) interested in a nuclear attack on Britain and b) capable of mounting one?’

Quite a few senior officers in all three services are, I believe, privately against this renewal, as they are aware that this country’s conventional armed forces are a shell - an array of ageing equipment, in diminishing quantities, manned by shrinking numbers of servicemen and women who increasingly lack the necessary training to handle them well in times of need, as the most experienced are most likely to leave, and the pressure this places on those who remain then drives more away.

I noticed (it is alas behind a paywall) the retired Major-General Sir Patrick Cordingley (he retired 15 years ago and so is free to speak as he wishes) wrote an article in ‘The Times today (11th November) making the case for getting rid of Trident. We don’t really control it, in effect it is part of the US Fleet. Its running costs are £4,000,000,000 a year and the replacement costs could run to £100,000,000,000 over thirty years, a strange expenditure for a country with an annual deficit of billions and an accumulated state debt of £1,500,000,000,000. I think these noughts are right. We could make much better use of this money.

Plainly, Sir Nicholas Houghton doesn’t agree with this, as I’ll discuss in a moment. He’s also very onside with the Cameron view of ISIS as an ‘existential threat to this country ( a view I think questionable. How much do they really care about us?) , saying: ‘And I think when the Prime Minister speaks like that, I don’t think he necessarily means in terms of they’re going to come and take our territory off us, but I think in terms of to undermine our way of life, our freedoms, our liberty, you know the values we stand for. I think that’s the true nature of the existential threat that a threat like ISIS does or has the potential to present.’

An interesting opinion but should we know he has it? If so, why? What would happen if he didn't have it, and instead said that he thought further interventions in the Middle East were a silly and dangerous waste of time? Would it be all right for him to say that on the BBC on Sunday morning?

Then there’s this :’ And if you’d indulge me, I think from a national perspective the only thing that we can unilaterally own as a country is a strategy about ISIS that keeps the country and the people of this country safe, and that’s why our national strategy is all about border security, the remarkable work of our intelligence services in intelligence led operations within the country, reaching out through the Muslim society within the country to assist them in deradicalising and delegitimising ISIS.’

This also sounds like the normal talk of a Tory cabinet minister – but is it right that it should be said by a senior serving general? Why should we know he thinks this? Would we be any worse off if he kept quiet?

What’s interesting is how vague and roundabout he becomes as soon as the really hot issue of his job – military spending – is discussed.

For example, this passage:

Sir Nicholas ‘…but I think the domestic situation has changed. I think we do have to sort of base as we look forward to this defence review, which should be one that is primarily about confidence and optimism and a reassurance to the people of the country, that there’s got to be a bit of realism in the fact that the world has become a somewhat more dangerous place. If you like, the latent threats have become patent ones.

ANDREW MARR: ‘So on defence spending George Osborne has promised you the NATO 2 percent, the extra spending, but are you concerned the Chancellor and the Treasury might start to kind of nibble away at that by adding things like military pensions into it?’

GENERAL SIR NICHOLAS HOUGHTON: ‘Well I think it would be a miracle if the Defence and the Treasury did not submit to NATO those things that it is permissible under the NATO rules to claim as national defence expenditure. My concern is that however the figures are done, there is real additional spending available for defence, and that is absolutely the case. And so if you like for the first time in a long time, probably 25 years, what this forthcoming SDSR is about is not the management of decline but the management of betterment.’

This hesitancy and qualification ( be honest - it''s not exactly a headlong charge in the general direction of the Treasury, is it?) slightly fade away when the subject of Trident and Jeremy Corbyn comes up.

ANDREW MARR: ‘...Of course we now have the leader of the opposition who says quite openly he would never press the nuclear button. Does that worry you? ‘

GENERAL SIR NICHOLAS HOUGHTON: ‘Well it … it would worry me if that, er, thought was translated into power as it were because … ‘

ANDREW MARR: ‘So if he wins, he’s a problem?’

GENERAL SIR NICHOLAS HOUGHTON: ‘Well there’s a couple of hurdles to cross before we get to that.’

ANDREW MARR: ‘Of course’.

GENERAL SIR NICHOLAS HOUGHTON: ‘But the reason I say this – and it’s not based on a personal thing at all, it’s purely based on the credibility of deterrence. The whole thing about deterrence rests on the credibility of its use. When people say you’re never going to use the deterrent, what I say is you use the deterrent you know every second of every minute of every day and the purpose of the deterrent is that you don’t have to use it because you successfully deter.’

ANDREW MARR: ‘So no point at all in spending billions and billions of pounds if our enemies think we’d never use it?’

GENERAL SIR NICHOLAS HOUGHTON: ‘Yeah because deterrence is then completely undermined. And I think people have got to … You know politic… Most of the politicians I know understand that and I think that, dare I say, the responsibility of power is probably quite a sobering thing and you come to a realisation “I understand how this thing works”.’

Well now: First of all there’s that ‘When people say you’re never going to use the deterrent, what I say is you use the deterrent you know every second of every minute of every day and the purpose of the deterrent is that you don’t have to use it because you successfully deter.’

Really? Once again, who and what are we deterring? Why do we need this vast American-controlled apparatus to do so, a complex and vastly technical thing whose main purpose is to bomb Moscow, which we no longer have any need to do, since the vast Soviet Army has been disbanded, the Warsaw Pact has ceased to exist and Moscow no longer dominates Europe in the absence of nuclear deterrence. as it so definitely did before 1989? By all means (here I differ with Sir Patrick Cordingley’s vapourings about the UN and setting an example, which are absurd) hang on to a few free-fall atomic bombs and fit our submarines with submarine-launched nuclear-tipped cruise missiles. But Trident? What is it for? Whose is it? Whom does it deter? How?

But then there’s the deep unwisdom of being drawn into political discussion. When asked about Mr Corbyn (or ISIS, or anything else) Sir Nicholas could perfectly easily have said that these were matters for politicians, about which he, a simple soldier, was not entitled to comment.

But this exchange :

ANDREW MARR: ‘So no point at all in spending billions and billions of pounds if our enemies think we’d never use it?’

GENERAL SIR NICHOLAS HOUGHTON: ‘Yeah because deterrence is then completely undermined’

And this one:

ANDREW MARR: ‘...Of course we now have the leader of the opposition who says quite openly he would never press the nuclear button. Does that worry you?

GENERAL SIR NICHOLAS HOUGHTON: Well it … it would worry me if that, er, thought was translated into power as it were because …

ANDREW MARR: ‘So if he wins, he’s a problem?’

GENERAL SIR NICHOLAS HOUGHTON: ‘Well there’s a couple of hurdles to cross before we get to that.’

...are serious breaches of the wise rule that generals stay out of politics. Andrew Marr has a story to get, and knows how to get it. The general, who could no doubt outfox a pincer attack in the field, fell straight into Field Marshal Marr’s trap and gave him the headline he wanted. 'Top General attacks Corbyn’s pledge not to use bomb.' Etc etc.

Of course a lot of pro-Tory Blairite politicians and media were really relaxed about this. But that’s because they think the public is right behind Trident (a thing most of them barely understand, and worship as a sort of fetish of machismo).

But what if the General had said instead that Trident was a colossal waste of money, was bleeding the defence budget dry, and served no observable military purpose.

Why, then the air would have been thick with yells about political generals speaking out of turn, and demands for his sacking. Well, if he’s allowed to say what he said on the Marr show, then he (or his successors) should equally well be allowed to say that Trident is a heap of worthless junk. You can’t have it both ways. Me, I still think generals should keep out of politics, always. Once you breach that principle, you endanger the constitution.

I also wonder what Mr Cameron really, really thinks in those long dark nights, when he ponders what he would do if he had to decide whether to retaliate to a nuclear attack ( I can’t think where it might come from, but never mind). I’d like to see someone press him hard on that.