Watermelons: the term used to describe the members of the Green party of England and Wales who are green on the outside and red on the inside. People in this faction are environmentalists, but when you cut them open, they bleed socialist ideologies.
Of the roughly 160,000 people that have flocked to the party since Zack Polanski became leader last year, most are thought to be in this camp, drawn to a political space on the left that they see as vacated by the Labour party.
But the author of a new book – The Green Socialist: Zack Polanski and the Battle for Britain’s Future – says this flavour of Green is nothing new. “What you’ve got to understand is that the party has been watermelon for at least 10 years,” says Russell Warfield, a former party staffer who has worked on election campaigns, including Polanski’s.
“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.”
His book unpacks the history of the party to explain how Polanski fits into it, arguing that the leader and his “eco-populist” package is not a departure from Green tradition, but the culmination of a 50-year evolution which has turned the party into the main electoral force on the British left.
Not everyone agrees. During the leadership election between Polanski and co-runners Adrian Ramsay and Ellie Chowns in 2025, a senior Green source described Polanski’s rise as a “hostile takeover”. Even Caroline Lucas, the Greens’ first MP and a former party leader, has said, when pressed, that she would love him to talk about the environment more.
“It’s just obvious nonsense,” Warfield says of the hostile takeover comment. “Look at the mandate, it was 85%,” he says of Polanski’s landslide leadership win. “He won across every wing of the party.”
But how green are the Greens? Since Polanski took over, he has been splashed across newspapers and TV screens discussing subjects ranging from Gaza to wealth taxes – progressive politics, but not necessarily or overtly green.
Warfield responds with a statistic: 34% of voters trust the Greens more than any other party on the environment, according to YouGov polling – the highest level of trust recorded for any party on any 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.”
Because of that starting point, he argues, the sensible move forward was to evolve into a broader message – one previous leaders paved the way for. “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.
“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.”
Warfield points out that many of Polanski’s positions are not his alone. Green party members vote on policy and the leaders are constitutionally duty bound to advocate for it. “Take the wealth tax,” Warfield writes. “He did not arrive at this policy personally. A ‘wealth tax’ is called for as ‘a means of limiting large accumulations of wealth’ in a Green party manifesto published long before Polanski’s leadership.”
The book finds links between the party’s past and present, even in unlikely places. It’s unavoidable, Warfield writes, that there were “some distinctly rightwing people present at the formation of the Green party”. The first key figure was Teddy Goldsmith, an environmentalist part of a famous Tory family. His writings formed key texts for People, the political party from which the modern Greens descend.
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But even Goldsmith – whose “deep ecology” philosophy leaned into Malthusian concerns about human population and misanthropic views that blamed humanity as a monolith for ecological degradation – shares threads with Polanski’s Greens, Warfield says. Both share the golden Green rule that infinite economic growth and endless extraction are impossible on a planet with finite resources. Both reject the idea that capitalism can simply carry on with business as usual, green or otherwise.
As the party has shifted towards social ecology over the years, Warfield says Polanski’s eco-socialism simply represents a modern evolution: arguing that capitalism and the 1% – not all of humanity – are the root cause of environmental destruction.
But Polanski’s tenure has also brought controversies. There was his criticism of the police response to the Golders Green attack, which the Met commissioner, Mark Rowley, called “inaccurate and misinformed”. There was the false claim he was a British Red Cross spokesperson and the sharing of a photo of a man with a T-shirt showing a guillotine and the phrase “we’re only making plans for Nigel”, a reference to Nigel Farage. YouGov polling shows Polanski’s approval rating has slumped since he became leader, while Green voting intention has dropped from 21% of the electorate in March to 11% this month.
Should the party take Polanski’s social media away? “Golders Green was a misstep,” says Warfield. “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.”
Polanski was criticised for his refusal to apologise for sharing the Farage guillotine picture. “Reform were trying to goad him into apologising for incitement to murder,” Warfield 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.”
On 8 October, Polanski will contest the Holborn and St Pancras byelection after Keir Starmer announced his decision to vacate the seat. Warfield thinks Polanski can win. “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.”
