NUCLEAR war is now a real possibility. Even the single use of a so-called tactical atomic warhead in Ukraine as a face-saving demonstration by a retreating Kremlin regime would legitimise nuclear war for the rest of the century.

All the existing nine nuclear powers – America, Britain, France, China, Israel, India, Pakistan, North Korea and Russia itself – would feel either emboldened or forced to factor an atomic exchange into their geopolitics. Armageddon looms.

Am I being unnecessarily alarmist? It is difficult to explain to current generations how we children of the 1950s felt about the appearance of nuclear weapons in the aftermath of Hiroshima and Nagasaki. The world of the 1950s and most of the 1960s believed it was permanently on the brink of an existential atomic war between the Soviet Union and Nato.

The Cold War was always code for the imminence of mutually assured destruction, or MAD in the parlance of the times. We went to school knowing the alarms could sound and that we in Britain would have only four minutes warning of death by rocket.

The current generation – certainly those born after the great powers negotiated fragile nuclear reduction treaties in the 1970s – know of nuclear war only as a theoretical possibility, not as something likely to happen tomorrow morning.

But in 1962, during the Cuban missile stand-off between Kennedy and Khrushchev, lessons at my school simply stopped when the American blockade came into effect, because we expected nuclear war that very day. That bleak spectre has now returned to the world following the Russian invasion of Ukraine and what has now become a de facto permanent military conflict between Nato and the Putin regime.

However, despite acres of press reporting about Putin’s nuclear sabre rattling, I don’t feel that the media, the political class, or people in general are appreciative of the line that has been crossed regarding the threat of nuclear annihilation.

Perhaps the current generation is too close to other forms of potential planetary extinction – through global warming or another pandemic – to single out atomic war as the supreme anxiety. In fact, I think the climate emergency takes precedence as an issue for most of those under 30.

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Yet there is a profound difference between the threat from nuclear war and the very real dangers arising from global warming and the likely crossing of the 2Cs barrier. Global warming is real, palpable and will affect all our lives. But it is a slow-motion catastrophe – which is not to minimise its consequences, particularly in the Southern Hemisphere. Nuclear war, on the other hand, could lead to a spasm of destruction that is instant and immediately fatal for billions of people.

Of course, it is a contest between the monsters Scylla and Charybdis to sink humanity, in which death is certain either way. But the nuclear Scylla will do it more quickly.

Am I just reliving the nightmares of my own childhood? I don’t think so. The world has been moving irrevocably towards the re-legitimising of nuclear weapons as “ordinary” since the turn of the 21st century. First, America and Russia have dismantled the rickety but still effective set of arms control treaties painfully negotiated in the 1970s and 1980s.

For instance, Donald Trump withdrew America from the 1987 treaty limiting cruise missiles, so the Pentagon could develop a new set of strategic atomic delivery systems. The so-called START 1 treaty expired in 2009. Its carefully drafted replacement specifically excluded new weapons systems, allowing the Pentagon and Moscow to concentrate on the next generation of atomic death. And last week, Putin suspended Russian participation in the New START treaty, effectively ending atomic arms control.

CONCURRENT with these legal shenanigans, the big powers have begun a major updating and expansion of their nuclear weapons capability – with little or no public debate. A world steeped in consumerism or – at best – preoccupied with climate change, has had no stomach for opposing the new generation of death machines.

Worse perhaps, Cold War pragmatism between the power blocs has been replaced by an arrogant US hegemony and the doctrine of liberal intervention. Increasingly, Western public opinion has been conditioned to favour interfering in other nations’ affairs (especially China) on grounds of “human rights” or “humanitarianism – as if the West was Simon pure.

In fact, as with China, this liberal interventionism is used to justify American military might and its nuclear expansion. After all, a global policeman needs a nuclear truncheon. So President Obama, that paragon of liberalism, set America on a course of nuclear “modernisation”, spending $1 trillion extra just on new atomic weapons systems.

This included 12 new missile-carrying submarines with a new missile system, a new strategic jet bomber, and – crucially – an upgrade to America’s so-called tactical nuclear bombs. This was liberal interventionism with a nuclear tip. No wonder Beijing and Moscow followed suit, though on a smaller scale.

The danger now lies in miscalculation. A cash-strapped Russia (with an economy the size roughly of Spain’s) has tried to bluff the West by threatening to use “tactical” nukes at an early stage in any land conflict. I doubt the West would use nukes tit for tat.

But if Russia crosses the nuclear line, Nato likely will give Ukraine the wherewithal to strike deep inside Russia with conventional weapons. Then we are on a roll to Armageddon.

The modern generation has never learned our 1950s fear of atomic radiation, the silent killer.

Nor of the prospects of a “nuclear winter” as the irradiated dust clouds ejected by atomic blasts blanket the globe, cutting off the sunlight.

What can we do to roll back nuclear war? A lot of faith is being put in the United Nations Treaty on the Prohibition of Nuclear Weapons. This attempts to create a legal framework that will effectively outlaw atomic warheads. That may sound pie in the sky but – the key proviso is that the treaty enjoins signatories to agree to a “no first use” of atomic weapons.

Nato rejects the treaty because it rejects making a “no first use” commitment. Note: this creates an impediment to a future independent Scotland joining Nato, if the SNP keep their avowed commitment to signing the treaty.

A “no first use” commitment is important in its own right. Britain and Nato should make such an undertaking now, regardless of the UN treaty on nuclear weapons. Allied to publicly rejecting extending Nato membership to Ukraine, it would be a clear signal to anti-Putin elements within the Russian establishment that the West seeks to avoid confrontation with Russia.

That might create conditions for peace in Ukraine and for the fall of the Putin regime. At the same time, forcing Nato to adopt a “no first use” stance would start to roll back the West’s remorseless slide towards adopting a new and destabilising nuclear capability.

How do we force Nato to adopt a “no first use” doctrine? That would require a new peace movement, undoubtedly linked to opposing Putin’s warmongering in Ukraine. A new peace movement that unites dissidents in the east as well as the west. And one that keeps the SNP committed to support for the UN Treaty.