Asked about their view of the Trident nuclear missile system, Britain’s armed forces chiefs have always insisted that they cannot comment because it was a “political” matter, not at all a “military” one.

General Sir Nicholas Houghton, chief of the defence staff, has now abandoned such caution, breaking a taboo by expressing a view that has huge constitutional implications. Britain’s most senior military officer has taken sides on an issue that is the subject of a highly charged political debate, and one in which tens of billions of pounds of taxpayers’ money are at stake.

Trident is useless. That’s why we must debate its renewal | Richard Norton-Taylor Read more

Asked on BBC1’s The Andrew Marr Show on Sunday if he was worried about Jeremy Corbyn’s admission that, if he were prime minister, he would never order the commander of a Trident submarine to fire a nuclear weapon, Houghton replied: “Well, it would worry me if that thought was translated into power.”

Corbyn’s position undermined “the credibility of deterrence”, Houghton said, adding: “The whole thing about deterrence rests on the credibility of its use. When people say ‘you are never going to use the deterrent’, what I say is you use the deterrent every second, of every minute, of every day. The purpose of the deterrent is that you don’t have to use it because you successfully deter.”

But the whole concept of nuclear deterrence, as Lord Alan West, former first sea lord and Labour security minister, pointed out on BBC Radio’s Today programme on Monday, was based on theory. Deterrence is based on a set of assumptions about an enemy’s intentions and responses. It is not “used” every second of every minute, in the way Houghton cleverly tried to explain.

Most weapons system are a deterrent. That is why the RAF has taken part in Nato exercises in the Baltic. Nuclear weapons are unique, not only because of their devastating humanitarian impact, but also in the UK’s case, a lack of credibility.

In an episode of Yes, Prime Minister, Sir Humphrey tells Jim Hacker, “it’s a deterrent”.

Hacker: “It’s a bluff. I probably wouldn’t use it.”

Humphrey: “Yes, but they don’t know that you probably wouldn’t.”

Hacker: “They probably do.”

Humphrey: “Yes, they probably know that you probably wouldn’t. But they can’t certainly know.”

Hacker: “They probably certainly know that I probably wouldn’t.”

Humphrey: “Yes, but even though they probably certainly know that you probably wouldn’t, they don’t certainly know that, although you probably wouldn’t, there is no probability that you certainly would.”

The common threat, to Russia as well as Britain, is violent Islamist terrorism. Neither Isis, nor any other extremist group of terrorists, or any other foreseeable enemy, is going to be deterred by Trident. Yet the government next year will ask MPs to vote on a new Trident system which Crispin Blunt, Tory chairman of the Commons foreign affairs committee, estimates will cost £167bn over its lifespan.

Jeremy Corbyn’s straight talking on Trident should be applauded | Simon Jenkins Read more

The government says Trident is needed as an “ultimate insurance”. No such insurance policy is in place in case of other potential disasters – pandemics, for example. Labour MPs echo the government’s line. They point to the number of jobs at risk if Trident were abandoned.

What MPs on both sides of the Commons seem most worried about is not whether the UK needs or would use nuclear weapons, but public opinion, and the loss of Britain’s status in the event of any unilateral decision to get rid of them.

In his memoir A Journey, Tony Blair said about Trident: “The expense is huge and the utility … non-existent in terms of military use.” In the end he thought giving it up would be “too big a downgrading of our status as a nation”.

The Guardian view on the generals and Jeremy Corbyn: if he is elected, he calls the shots | Editorial Read more

Other factors, not Trident, affect Britain’s status, as the Guardian’s story on foreign policy today suggests. Britain is suffering a crisis of confidence in foreign policy that leaves it “sidelined in Syria, ineffective in Ukraine, unwilling in Europe, and inimical towards refugees”, as a report by some of Britain’s most senior former diplomats, intelligence officers and foreign policy academics has warned. All this, despite having nuclear weapons.

Houghton seems to have attempted, by his intervention on Trident, and backing those Labour MPs who differ from the views of their leader, to close down a debate. He might after all have done us a service, despite crossing a red line, if he has opened one up on this most important, but neglected, issue.