When Zack Polanski assumed the leadership of the Green Party of England and Wales last year, he inherited a membership of roughly 160,000 new recruits — a surge that has fundamentally reshaped the party’s identity. Most of these newcomers, by all accounts, are what political insiders have long called “watermelons”: green on the outside, red on the inside. They are environmentalists, yes, but their political blood runs socialist.
They came looking for a home on the left that Labour, under its current leadership, no longer seemed willing to provide.
Yet according to a new book by Russell Warfield — a former Green Party staffer who has worked on election campaigns including Polanski’s — this ideological character is not some sudden transformation imposed by a charismatic new leader. It is, he argues, the fruit of a half-century of organic evolution.
A Movement, Not a Coup
Warfield’s book, *The Green Socialist: Zack Polanski and the Battle for Britain’s Future*, traces the party’s lineage back to the early 1970s, contending that the fusion of ecological and socialist thought has been embedded in the Greens’ DNA for at least a decade, with deeper roots still.
“There’s often this dichotomy presented that there’s this ‘real core’ Green party who are these ecologists who really just care about conservation of the environment, then there’s this new cohort of hard leftists,” Warfield says. “Actually, this has been both an organic process but also one which reaches much more deeply into the past of the party, where a lot of the fundamental positions of the party can be traced back to the early 1970s.”
Not everyone in the party shares that reading. During the 2025 leadership contest — in which Polanski defeated Adrian Ramsay and Ellie Chowns — a senior Green source characterised his ascent as a “hostile takeover”. Caroline Lucas, the party’s first MP and a former leader, has herself admitted, when pressed, that she would prefer Polanski speak more about the environment.
Warfield dismisses the takeover narrative outright.
“It’s just obvious nonsense,” he says. “Look at the mandate, it was 85%.” That figure refers to Polanski’s landslide leadership victory. “He won across every wing of the party.”
From Conservation to Eco-Populism
Since taking the helm, Polanski has dominated news cycles — but not always for reasons one might expect from a Green leader. He has spoken forcefully about Gaza, championed wealth taxes, and staked out positions on a range of progressive causes that, while politically left, are not overtly environmental.
Warfield counters with a striking data point: YouGov polling shows that 34% of voters trust the Greens more than any other party on the environment — the highest level of trust recorded for any party on any single issue. “There is not a voter in this country, leftwing, rightwing, old, young, rural, urban, whatever, that does not strongly associate the Green party with taking action on the environment,” he says.
Given that starting point, Warfield argues, the strategic logic of broadening the party’s message was not just sensible but overdue. Previous leaders, he notes, had already begun paving that road. “The reason the party exists is in recognition of the fact that just having a bunch of environmental conservation movements isn’t addressing the root political and economic causes of environmental degradation,” he explains. “We tried 50 years of that. And it got us so far, but the manifest moments of material advancement have been tied to moments where we’ve been able to be more responsive to the actual political context of the day.”
Crucially, Warfield points out that Polanski’s policy positions are not personal inventions. The Green Party’s constitution requires leaders to advocate for policy decided by the membership. The wealth tax, for instance — a signature Polanski talking point — was called for as “a means of limiting large accumulations of wealth” in a Green Party manifesto published well before his leadership began.
Unlikely Roots and Modern Echoes
The book delves into some uncomfortable corners of the party’s origins. Warfield acknowledges that there were “some distinctly rightwing people present at the formation of the Green party”. The most prominent was Teddy Goldsmith, an environmentalist from a well-known Conservative family whose writings formed foundational texts for People, the political party from which the modern Greens descend.
Goldsmith’s “deep ecology” philosophy leaned into Malthusian anxieties about human population and held misanthropic views that blamed humanity as a whole for ecological destruction. Yet even here, Warfield finds threads connecting past to present. Both Goldsmith and Polanski’s Greens share what Warfield calls the golden Green rule: that infinite economic growth and endless extraction are impossible on a planet with finite resources. Both reject the notion that capitalism can continue with business as usual.
The difference, Warfield says, is one of evolution rather than rupture. As the party shifted over the decades towards social ecology, Polanski’s eco-socialism emerged as a modern refinement — one that identifies capitalism and the wealthiest 1%, rather than humanity in its entirety, as the root cause of environmental destruction.
Controversy and the Cost of Authenticity
Polanski’s leadership has not been without turbulence. He drew sharp criticism for his comments on the police response to the Golders Green attack, which Met Commissioner Mark Rowley described as “inaccurate and misinformed”. He falsely claimed to be a British Red Cross spokesperson. And he shared a photograph of a man wearing a T-shirt depicting a guillotine alongside the phrase “we’re only making plans for Nigel” — a pointed reference to Nigel Farage.
The political toll has been measurable. YouGov polling shows Polanski’s personal approval rating has declined since he took the leadership, while Green voting intention has fallen from 21% of the electorate in March to 11% this month.
Should the party rein in his social media presence? Warfield is measured but firm. “Golders Green was a misstep,” he concedes. “But what you don’t want to do is to get to a situation where every post needs double-tick signoff from different members of staff and you can’t just let Zack engage with social media in the way that allows him to reap the political points of authenticity.”
On the Farage guillotine image, Warfield is unapologetic on Polanski’s behalf. “Reform were trying to goad him into apologising for incitement to murder,” he says. “If you do that, you legitimise the claim that they’re making. I think there’s a lot of strength in not succumbing to the pressure of playing that game.”
The Holborn and St Pancras Test
On 8 October, Polanski will contest the Holborn and St Pancras byelection, triggered by Keir Starmer’s decision to vacate the seat. Warfield believes victory is within reach.
“You could vote Labour again and you get another backbencher who is one among literally hundreds of Labour MPs and that doesn’t make much difference to anything,” he says. “Or you can put a really prominent, independently minded Green in there and continue to put pressure on the Burnham project from its left.”
It is, in microcosm, the pitch Polanski has been making to the country: that the Greens are no longer a single-issue pressure group, but the principal electoral vehicle for a left that feels politically homeless — and that this transformation has been decades in the making, not months.
Why it Matters
The Green Party’s evolution from a conservation-minded pressure group into Britain’s most visible left-wing electoral force represents one of the most significant realignments in recent British politics. Whether Polanski’s eco-populism proves to be a durable political project or a fleeting moment of momentum may well be decided on 8 October in Holborn and St Pancras — but the broader question it raises is already pressing. If Labour continues to occupy the centre ground and the Greens consolidate the left, British politics may be entering a period of genuine multi-party competition, one in which the old assumptions about who owns the progressive vote no longer hold. The watermelons, it seems, have ripened.