We must be clear-sighted. There is no way to be prepared for a nuclear attack, you have to stop it happening – and that must be our most urgent task today, warns CND leader Kate Hudson.

We are living in a new and uniquely dangerous situation; because never before has the world been at such great risk of nuclear war. Maybe you think I’m overstating the case — but here’s why not.

When the US used two atom bombs in 1945, one on Hiroshima and one on Nagasaki, an estimated 340,000 people died as a result.

That was a catastrophe, and an unnecessary catastrophe, because Japan was already trying to surrender. But at that time only the US had nuclear weapons.

There was no possibility of a nuclear war breaking out.

And then think about the Cuban missile crisis, when it seemed that the world was on the brink of disaster; the two leaders, John F Kennedy and Nikita Khrushchev had the wisdom to negotiate to bring about a solution which dealt with the security concerns of both sides. Wisdom and dialogue prevailed and nuclear war was averted.

But look at the situation now: what are the unique factors that make nuclear war so much more likely?

Firstly, there is a terrible and brutal war taking place in Ukraine, people are dying, homes and infrastructure torn apart.

We are right to be so outraged, to want this war to stop. A war like this is the context in which nuclear weapons could become the next stage in military escalation.

Secondly, where are the calls for peace, the negotiation, the concern for saving every human life that we should be hearing from our leaders?

It’s just not there. What we’ve been hearing, even when it was still possible to prevent this war, is bellicose rhetoric, followed by escalatory movements of troops, weaponry and munitions that can only make matters infinitely worse.

We’ve seen the most heartbreaking coverage of the sufferings of the Ukrainian people, and our hearts go out to them.

But at the same time we have wall-to-wall coverage promoting warfare, even encouraging people to go and fight.

Every single death is a tragedy and the media and politicians who suggest otherwise, and pursue policies that will lead to more slaughter should be ashamed of themselves.

This is the reality of war and it has to stop.

But what of the reality of nuclear war?

The heart of a nuclear explosion reaches a temperature of several million degrees centigrade. This results in a heat flash over a wide area, vaporising all human tissue. Beyond this central area, people are killed by heat and blast waves, with buildings collapsing and bursting into flame.

The firestorm creates hurricane force winds spreading and intensifying the fire.

As in Hiroshima, many who survived the immediate blast died shortly afterwards from fatal burns. Others died because of the complete breakdown of rescue and medical services which had themselves been destroyed.

Then radiation kicks in, with symptoms of nausea, vomiting, bloody diarrhoea and hair loss. Most of these victims died within a week.

With radiation, there is no place to run to, no place to hide; if you escape the blast you cannot shut the door on radiation. It poisons and destroys, it brings sicknesses, cancers, birth deformities and death. This is the least we can expect from nuclear use.

Because as if that isn’t bad enough, the Hiroshima bomb was actually a small nuclear bomb in today’s terms. Some of today’s nuclear weapons are 3,000 times the power of the Hiroshima bomb.

Can you imagine what that would do to London? How is it that Sadiq Khan’s office can say that London is well-prepared if Vladimir Putin launches a nuclear attack? There is no way to be prepared for a nuclear attack. You have to stop it happening.

That is our most urgent task because it is in this time of escalating war, with nuclear arsenals on both sides — this completely new and unique situation, that we have to do everything possible to prevent nuclear use.

And of course the recent policies of nuclear weapons states are not making it easy. For some decades we had seen gradual reductions in nuclear weapons, but now we are seeing modernisation programmes on all sides — like Britain’s Trident replacement at a cost of over £205 billion.

In some cases we are even seeing increases — like Boris Johnson’s nuclear arsenal increase last year. But worst of all is the sanitising of the idea of nuclear use.

Donald Trump has a lot to answer for this: he not only talked of so-called “usable” nuclear weapons, he also produced them and deployed them in his last year of office.

So now the idea that they will never be used — the mutually assured destruction theory of the cold war — has gone.

We hear of tactical nuclear weapons, as if you could use a small one on a battlefield and everything would be fine elsewhere. This is complete nonsense — and criminally dangerous nonsense.

So what can our leaders be thinking? Those who talk of no-fly zones, those who are piling on the pressure for this, whether senior figures in government and Parliament and from the military establishment, must know that this is escalation to actual direct war between nuclear powers.

Polls currently show only minority support for a no-fly zone, but this can change if politicians and media don’t get off the 24/7 promotion and glorification of war.

There are 12,000 nuclear weapons held by Nato states (the US, France and Britain) and Russia. With delivery systems capable of intercontinental delivery, these can all be focused on Ukraine, but it’s much more likely that they would be firing on London, New York, Paris, Moscow and indeed pretty much anywhere else.

The one thing we can be sure of, is that having nuclear weapons makes you a target. So what can we do?

We must build pressure on government to change course. We must make people aware of the consequences of war, the existential threat that we face.

We must get out on the streets and shout it out — people need to hear this, whether or not they want to.

We must build the peace movement here and internationally — there are huge protests taking place for ending this war; we must give ever greater support to the courageous peace protesters across Russia, as they face arrest and imprisonment for their actions.

All our work, all our actions in these terrible days, must be to secure a future for humanity, for all peoples.

It is truly now, above all else, the time to protest and survive.

Kate Hudson is general secretary of Campaign for Nuclear Disarmament. This article has been first published in The Morning Star