In the next few hours, the end of human civilisation may commence. We’ve had a good run – about 6,500 years, actually – and now we will perish in fire, famine, drought, never-ending winters, disease and chaos. A single megaton nuclear weapon dropped on the House of Commons would kill more than a million people outright. Nearly 2.5 million would be burned, maimed and injured. The fireball radius – the area that represents total annihilation – would stretch for nearly a kilometre.

That’s just one bomb, of course. What if 100 nuclear warheads with a much lower yield – 15 kilotons, say, the size of the bomb dropped on Hiroshima – were exchanged on the Indian subcontinent? Well, scientists have modelled this scenario, and the calamity extends far beyond the borders of India and Pakistan. As five megatons of black carbon instantly enter the atmosphere, temperatures will suddenly fall, rainfall will decline, the ozone layer will thin dramatically and the frost-free growing period for crops will shorten by between 10 and 40 days. According to the International Physicians for the Prevention of Nuclear War, 2 billion people could starve in the aftermath. In a full east-west exchange billions would also die. Infrastructure would collapse. The survivors would, it is often said, envy the dead. They would suffer torturous protracted deaths from radiation; they would scrabble for food in irradiated soil; as healthcare systems implode, their illnesses and cancers would be untreated. For the diminishing minority who remained alive, it would be everyone for themselves in a struggle for survival in a ravaged hellscape.

Why inflict this horror on your imagination? It seems so abstract and distant, and yet, according to the Doomsday Clock of the Bulletin of the Atomic Scientists, we are but two minutes from midnight. The US and Russia combined have around 2,000 nuclear weapons on a hair trigger, meaning they could be launched in minutes, leaving my scenarios just hours away.

There have been many close calls. In 1979, Zbigniew Brzezinski – President Carter’s national security adviser – was woken up at 3am to be told that 250 Soviet nuclear missiles were heading to the US. If the president were to retaliate, he would have between three and seven minutes to decide. An updated report came through: there were 2,200 missiles. Armageddon beckoned. But the reports were wrong. “Someone had mistakenly put military exercise tapes into the computer system,” as the former defence secretary Robert Gates put it. Consider today, with Donald Trump in the White House facing off against North Korea’s Kim Jong-un. A nuclear arsenal on a hair trigger under the control of a man whose Twitter feed is a never-ending temper tantrum is not exactly reassuring. Millions could perish in a nuclear conflagration in a matter of hours.

Which brings me to the noble but marginalised cause of nuclear disarmament. This Sunday marks 60 years since the first march to Aldermaston – where Britain’s nuclear bombs are produced – which spawned the Campaign for Nuclear Disarmament (CND). There is a certain paradox in the fact that a supporter of nuclear disarmament leads the Labour party, and yet the cause is barely on the nation’s political radar, even as Kim pledges to de-nuke the Korean peninsula. That’s because Labour’s leadership has made a strategic decision to accept party policy, which is to renew Trident.

Cards on the table: I’m a unilateralist but I’ve accepted Labour’s position. It depends how the question is phrased, but polling does not suggest any substantial public appetite for unilateral disarmament. Many unions are opposed. Such a policy would reopen a civil war with a Labour right that is already increasingly febrile. With the priority being to transform Britain with socialist policies, such a compromise seems sad but unavoidable. And yet the arguments for replacing Trident are based on utter delusion, the cost of acting on these delusions is grotesque, and we are rendered colossal hypocrites by lecturing the world about weapons of mass destruction while renewing our own. CND believes the lifetime cost will be at least £205bn. What would that money mean for an NHS that last year, the Red Cross said, faced a “humanitarian crisis”; for our struggling education system; and for eliminating the housing crisis?

Listen to Tony Blair’s former defence secretary Des Browne, who suggested that cyber attacks against Trident could render it obsolete. Or take former Tory defence secretary Michael Portillo, who said that Trident’s replacement was “a waste of money” and that “our independent nuclear deterrent is not independent and doesn’t constitute a deterrent”. Tony Blair himself said he could see “the common sense and practical argument” against Trident, that “the expense is huge, and the utility in a post-cold war world is less in terms of deterrent, and nonexistent in terms of military use”. So why throw all that money at it? Because in Blair’s own words it would be “too big a downgrading of our status as a nation”. All that wasted money for status alone.

There’s more wisdom from the Tory Crispin Blunt, when he was chairman of the Commons foreign affairs committee in 2016, who said: “At what point is it no longer value for money in the UK? In my judgment we have reached that point.” We fail to adequately tackle the actual threats facing Britain and leave our conventional forces under-resourced because of the Trident obsession. Nearly a decade ago, Field Marshall Lord Bramall – former head of the armed forces – and two senior generals described nukes as “completely useless as a deterrent to the threats and scale of violence we currently face or are likely to face”. Take terrorism, take cyber-attacks, take climate change: all pose grave, demonstrable threats to our security. Yet we are failing to invest in tackling them, while billions are thrown at weapons of mass destruction that do not keep us safe. Labour policy cannot shift until public opinion does decisively. As the cold war revived in the early 1980s, CND led mass national campaigns that began to shift opinion: the same is needed today to stop this madness (and it is madness). There are other steps that can be taken in the meantime. Labour should be campaigning for Russia and the US to cease putting their arsenal on hair-trigger alert. They should exert moral pressure on other nations to sign up to the comprehensive test ban treaty. Britain cannot disarm the world, but it can set an example. The nightmare of nuclear apocalypse hangs over humanity. It will one day become a reality, unless we stop it.

• Owen Jones is a Guardian columnist