I ventured out into Westminster earlier this week to take a look at the Extinction Rebellion protest and it reminded me of the Edinburgh Fringe. I don’t just mean the sheer number of people in fancy dress, such as the Red Rebels with their red robes and white face paint, or the men in gas masks. I mean it was like a huge piece of political street theatre written by a brilliant satirist.

Wherever you looked there were little comic vignettes. At one point, having become slightly numb listening to one activist after another condemn ‘western consumerism’, I popped into Pret a Manger, only to be confronted by protestors politely queuing up to buy vegan baguettes. I could have sworn some of them were the very same people who’d been holding up signs saying ‘End Capitalism’ moments before. Then there was the hearse parked in Trafalgar Square, complete with a coffin in the back labelled ‘Our Future’, which immediately got a parking ticket.

Apart from that over-zealoustraffic warden, the reaction of the authorities was a model of restraint. At first I found the police’s failure to enforce the law irritating — I joked to James Delingpole that if it were a group of Catholic nuns protesting about changes to the Gender Recognition Act, the riot squad would have been straight in with the tear gas. But I came around to this policy as the day wore on. Rather than turn the demonstrators into martyrs by arresting them en masse and dragging them into paddy wagons, the police stood back for the most part and let them make fools of themselves.

On the day I was there, first prize went to Mark Rylance, who gave a speech saying he’d been inspired to resign from the Royal Shakespeare Company by Greta Thunberg. Apparently, the 59-year-old actor hadn’t realised BP’s £7.5 million sponsorship deal with the RSC, which has enabled 80,000 young people to buy tickets for £5, was immoral. The 16-year-old oracle had opened his eyes (and the RSC has severed ties with BP).

For all the demonstrators’ talk of ‘science’ and their insistence on telling ‘the truth’, it could not have been clearer that this global movement is a religious cult. Several of the protestors seemed to be in an emotional fugue state, their eyes burning brightly, like evangelicals possessed by the Holy Spirit.

Many people have made this observation before, but the protestors’ apocalyptic moralism — their absolute conviction that the world will end in our lifetimes if we don’t purge ourselves of sin — is a textbook hallmark of millenarianism. It has a good deal in common with Christianity in its febrile, late medieval phase, with Saint Greta as Joan of Arc, but it’s also post-Christian in the way predicted by Chesterton. I’m not thinking of his supposed comment about people believing in anything rather than nothing when they stop believing in God, although there was some evidence of that, with different groups embracing paganism in various forms. I’m thinking of another quote: ‘The modern world is full of the old Christian virtues gone mad.’

The odd thing is that none of the protestors was aware that they were in the grip of these religious ideas, even though it was obvious to any outsider. And this too gave the affair a rich comic dimension. The highpoint of my day was witnessing a speech given by the Guardian columnist George Monbiot on Millbank. It was dusk and he was surrounded by hushed congregants sitting in a circle. He stood on a small box and delivered what was, in essence, a religious sermon. He talked about how he and his fellow eco–warriors were kind, altruistic people, rebelling ‘with love in our hearts’ against an ‘avaricious’, ‘vampiric’, ‘necro-philic’ economic system kept afloat by ‘neo-liberals’ and ‘psychopaths’. ‘If we love ourselves, we must purge this toxic system built around capitalism from our souls,’ he said. The talk ended with some call and response, with George shouting out ‘Extinction!’ and the crowd replying ‘Rebellion!’ It was like a scene from a 21st-century equivalent of The Life of Brian, except in this version the protagonist has embraced his messianic status.

Am I being too flippant about what could metastasise into a violent doomsday cult in the same mould as Aum Shinrikyo, the group that carried out the Tokyo subway sarin attack? Probably. But for the time being it’s hard not to laugh.