A promising future now looks perilous for election loser Zack Polanski. He sowed, now he reaps | John Harris

As ever, among all the noise triggered by Labour holding the seat of Holborn and St Pancras, the most plain-spoken and undeniable analysis was provided by that sage and national treasure John Curtice, of Strathclyde University. The result, he said, echoed national opinion polls, and reflected two undeniable facts: that the Greens are in need of a period of contrition and reflection, and Labour ought to be slightly less than ecstatic.

Andy Burnham’s party, with a majority of 3,364, he said, showed they “are in a much better position than they were six months ago, but still not as popular as they were in 2025”. The Greens, meanwhile, remain “a more significant player than historically they have ever been”, but have lost much of the ground they gained during Zack Polanski’s first year as leader, when the serial failures of the local MP – one Keir Starmer – provided him and his party with such a glorious succession of political opportunities.

Do not forget: the Greens’ success earlier this year in Gorton and Denton played a massive part in Starmer eventually leaving the political stage, and the man he barred from being the Labour candidate snatching his job. But now? Publicly, Polanski seems largely unrepentant about the “Zionism is racism” motion passed at his party conference, and confident he can resume where he left off. But his party’s claim that it tripled its previous vote share in the seat is very specious indeed: as the pollster Peter Kellner puts it, “the leftwing vote two years ago was divided between the Greens’ 10.4% and an independent, Andrew Feinstein’s, 18.9%. Together, they won 29.3%.” The true increase in the leftwing anti-Labour vote, therefore, is just 3.5 percentage points, and Polanski has thus taken such a significant blow that his experience of the next few weeks and months could be very choppy indeed.

Over the last week, I spent two days in the constituency, filming another episode of the Guardian’s Anywhere But Westminster video series, and got a deep sense that our politics remains in a state of unpredictable flux. So many people and the conversations we had come to mind. The young people of colour in the pinched neighbourhood of Somers Town – the urban village right next to Euston station – who were all voting Green, and talked of Gaza and the impossibility of living in our capital. The woman in upscale Primrose Hill who told us she no longer told people she was Jewish for fear of instant uproar, and upbraiding about Israel, a country she had last visited 15 long years ago. But most of all, a 24-year-old trainee teacher called Tom, who reluctantly still lives with his parents, and has no idea how he is going to hold down a job in his home city. He had once been an enthusiastic Green member and activist, he told me, and had every intention of voting for them, until the Zionism motion at the party’s conference suggested a party perfectly happy to inflame the UK’s sense of division and polarisation, and he decided to switch to Labour.

The searing summer should have provided the Greens with another boost, and a real chance of another byelection win. But now? Polanski – who endorsed the idea that Zionism is a form of racism eight days before his party’s conference began – looks not just morally questionable, but distinctly weak: one central bit of symbolism in this whole affair, let us not forget, was his absence from the Zionism debate and vote at his party conference.

And so to a geographical jump to a few other parts of the country. As I may have written once or twice in the past, I live in Frome, in Somerset: a 25,000-population settlement whose affinity with the Greens has been deepening for the last decade or so. They provide four of the six councillors who represent the town on our new unitary council. The rurality and climate-fear in the villages that surround us chimes with Ellie Chown’s seemingly out-of-the-blue election two years ago as the Green MP for North Herefordshire and Adrian Ramsay’s success in the East Anglian seat of Waveney Valley. But there are also elements of the maverick, future-facing attitudes that waft down into our neck of the woods from Bristol Central, the seat held since 2024 by Carla Denyer, the former Green party co-leader. I think I know what was holding those two elements together, and partly powering the Greens’ resurgence: a mixture of radical, empathetic social democracy and urgency about the fate of the planet that also seems to have taken root in some of England’s suburbs.

With the possible exception of Bristol, If you wanted to completely wreck the Greens’ successes in all those places, you would bin that approach and accelerate exactly what Polanski has facilitated: not just a politics of no-surrender and provocation, but the entry into the party of embittered former Jeremy Corbyn supporters and assorted ultra-leftists, bringing with them a flimsy, pious gesture politics.

The party’s former leader, Caroline Lucas, and the long-standing Green activist Rupert Read are about to publish a mini-manifesto titled Climate Popularism: a guide to “breaking the grip of rightwing populism through a new politics of crisis resilience”, to be formally launched on 15 October. Written before the antisemitism meltdown, it rather minces its words about Polanski’s project, but makes it pretty clear why things have now gone wrong: “Some observers have wondered whether this new eco-populism has at times been a little too quiet about the ‘eco’ part,” Lucas and Read write. “On the doorstep, at least, this may be an understandable strategy … [But] as recent heatwaves have made abundantly clear, the salience of climate impacts will make adaptation concerns a doorstep issue before long.”

Lucas and Read make the case for “centrally funded, locally appropriate action to adapt neighbourhoods, infrastructure and ways of life, to prepare for the broad, cascading impacts of human-triggered climate change”. They propose a domestic retrofit programme that would entail a lot of “secure green jobs”. They also write, very perceptively, about an “exhausted majority” tired out by our shrill politics, and suggest the “depolarisation” of the climate issue in the face of plain facts – which sounds like the direct opposite of how Polanski operates. There is talk of a politics of “courage, hope, love of place” – and, crucially, a decisive turn into the use of citizens’ assemblies. This is the kind of turn the Greens should undoubtedly take – but even if they do, they will now be starting in a deeply troubled and weakened state.

Burnham, meanwhile, still has no end of work to do. For what it’s worth, many of us have long believed that the substantial presence in British politics of a radical party free of Labour’s pussyfooting around the climate crisis and the harsh realities of inequality was an absolute necessity, and the Greens’ fitful growth was nothing but a good thing. Now, by contrast, as the fall-out from Polanski’s sudden crash only deepens, they have a massive amount of self-questioning and reinvention to do. Whether they will even have the inclination is another question entirely.