A strange scene greeted tourists in Westminster on Thursday, as three green activists stood on top of a fire engine posing for photographers.

The engine was parked in front of the Treasury, a building they had just attempted to spray with 440 gallons of fake blood. Standing a few paces off were scores of police officers, waiting in silence.

The activists, from Extinction Rebellion (XR), believe they know exactly what is happening to our planet and how we must tackle it, but they do not know how to operate a fire hose.

The engine was parked in front of the Treasury, a building they had just attempted to spray with 440 gallons of fake blood

So after an initial burst against the Treasury, the protesters lost control and the hose went snaking around the pavement, spraying red paint around the floor and over any passers-by.

As I watched the police ranks in the aftermath, there was one thought above all: ‘Why are you just standing there doing nothing?’

If someone had parked their car at the back of Whitehall, it would have been towed away in a matter of seconds, yet these green fanatics had placed a fire engine outside one of the most prominent sites in the country.

After an initial burst against the Treasury, the protesters lost control and the hose went snaking around the pavement, spraying red paint around the floor and over any passers-by

They had unveiled a banner that read ‘Stop funding climate death’ and defaced a Government building while the police did nothing, aside from offer some background colour for XR publicity shots.

That passivity is depressingly typical – and the result is that green extremists are encouraged to do whatever they want unchallenged.

It was the same last April when the group tried to bring London to a standstill. As bridges and major thoroughfares were shut down by XR protesters – bringing misery to ordinary members of the public – the police again seemed to think their role was to be mere observers. Or party-goers.

The protesters managed to shut down the whole area around Oxford Circus, costing millions of pounds in lost business on one of Britain’s busiest shopping streets.

And what did the police do? A number of them were caught on camera dancing in a ‘rave’ with the protesters. At Waterloo Bridge, an officer was seen on a skateboard.

It was as if the constabulary wanted to be loved. No care for the thousands of Londoners whose business had been damaged.

Red paint flooded the road outside the Treasury in London as protesters held a banner

No thought for the many people who just wanted to get from one side of the city to another without being told they couldn’t by a group who always think they know best on absolutely everything.

It is true that there were arrests following last week’s pantomime outside the Treasury, and a police raid on a house in South London yesterday suggests they may finally be getting on the front foot.

But the supine response to the fanatics of XR is something which this country needs to address – and quickly.

For the group is planning to bring our capital to a halt repeatedly. They have even threatened to prevent the Queen’s Speech.

Their refusal to acknowledge any view but their own deranged belief and their defiance of democratic norms is authoritarian, even fascistic. Just who do they think they are?

As I watched the police ranks in the aftermath, there was one thought above all: ‘Why are you just standing there doing nothing?’ Pictured, police escorted the truck on October 3

The claims of Extinction Rebellion need to be disputed from their very roots. Despite the childish certainty these extremists promote, the science of climate change is deeply contested.

Most scientists agree there are variations going on but they disagree on exactly what the causes are. And, most importantly, there is almost no agreement on how to address them.

In recent months, 16-year-old Swedish school-truant and activist Greta Thunberg has (like XR) been trying to persuade people that the problem is straightforward

Even if the science is exactly as XR claims it is, it does not follow that the group’s draconian solutions are correct.

In fact, the answers they do offer are the worst ones possible, the equivalent of urging people to avoid death by old age by shooting ourselves now.

In recent months, 16-year-old Swedish school-truant and activist Greta Thunberg has (like XR) been trying to persuade people that the problem is straightforward and the answers clear: we must engineer the complete destruction of the global economic system.

They blame ‘capitalism’ in particular, betraying the fact that many of these global-warming ideologues are little more than warmed-over communists.

XR and those like them ask that we should trust their claims and then volunteer to become immeasurably poorer.

How they will persuade the Chinese (the world’s biggest polluters) to agree to this plan, nobody can say.

But they are happy to immiserate countries like this one first. And they claim that the system of economic growth, which, in this century, has already halved the number of people living in absolute poverty globally, is what needs destroying.

It is time we stopped humouring this fanaticism. Everywhere they exaggerate and catastrophise.

If someone had parked their car at the back of Whitehall, it would have been towed away in a matter of seconds, yet these green fanatics had placed a fire engine outside one of the most prominent sites in the country. Pictured, an activist is helped down from the vehicle

For instance, they claim that we are in the middle of a ‘climate emergency’, that more than a quarter of threatened species are now threatened with extinction.

And they also claim that rising sea levels in the next 15 to 30 years will wipe out whole communities.

Every one of these assertions is contested. Even the Intergovernmental Panel on Climate Change (IPCC) does not come to conclusions anything like those claimed by Greta Thunberg and XR – and no serious authority comes even close to supporting the crazy, end-of-times theology now gripping the green movement.

If anyone doubts the fanatical nature of XR, listen to Roger Hallam, who leads XR in the UK and who organised the recent protests in London.

Hallam – like Thunberg – speaks and acts like a figure from the Middle Ages. With his deranged, glassy-eyed stare, he cries that the end is nigh and calls for acts of mass repentance by the sinners of the general public.

Nothing will persuade him that his ideas and tactics may be wrong. In a recent interview, Hallam was asked if he would dedicate the rest of his life to XR. The answer was instructive. ‘Yes,’ he replied, ‘because we’re all going to be dead soon, so there’s nothing else to do, is there?’

The tone is one of pure fanaticism. You can hear it when Thunberg delivers her unhinged sermons to the credulous global elites.

WHEN, for example, this privileged young girl berates the leaders of the world for ‘stealing’ her childhood – as though anyone other than her parents ever asked her to spend her time travelling around the world hectoring others on things she barely understands.

The protesters managed to shut down the whole area around Oxford Circus (pictured on April 19), costing millions of pounds in lost business on one of Britain’s busiest shopping streets

It is the adults, of course, who are to blame, for even St Greta merely voices what she has been told to say and influenced to say by her parents and others.

Likewise, across Britain the teachers are indoctrinating pupils into a cult of climate alarmism – and then insist that we must listen to the children because it is only the young who have the wisdom to see the true extent of the catastrophe.

The result – as families up and down the country will know– is many of our children actually believe that they will never reach old age. And that before they have grown up, they will be consumed in a great ball of fire.

It is wicked to terrorise the young like this, to pretend that the children know best, to claim to be certain about things we do not know enough about. And to pretend that Extinction Rebellion, the most extreme people of our time, must be placated.

If this madness is to be stopped then adults, from teachers to the police, must reassert themselves and do the jobs they are paid for. They should stop colluding in this avalanche of law-breaking.

Otherwise, this era will be looked back upon in amazement by our children’s children, who will want to know: how did the luckiest generation in history throw it all away on the say-so of one little girl and a bunch of anarchists who couldn’t even operate a fire truck?