Just eight months ago the Green Party of England and Wales sent shivers through the Labour establishment when it overhauled their 13,413-majority in Gorton and Denton to win a convincing by-election victory with more than 40 per cent of the vote.

Galvanised by the leadership of Zack Polanski it seemed the Greens were about to emerge as a serious force in UK politics as the Labour Party tumbled in the polls under Sir Keir Starmer.

Now, after a disastrous conference vote last week, serious questions are being asked about Polanski’s leadership following his failure to make any inroads as a candidate in the key target seat of Holborn and St Pancras.

On its own, a reasonable second place in what is after all a Labour stronghold and Starmer’s vacated seat would not mortally wound a Green leader. But the loss has exposed deep divisions in the party as the traditional old guard question what they regard as Polanski’s failure to curb the excesses of new left-wing members.

‘Toxicity’ around the Green brand

At the core of the dispute is the controversial vote last Sunday at the party’s conference to pass a motion describing “Zionism as racism”. Critics argue the motion effectively says Israel does not have a right to exist. It has been roundly condemned from within and outside the party.

Polanski is now facing sustained criticism for not only not voting on the motion, but of being “missing in action” in not fighting to impose control on the radical elements of his party.

The Greens have seen a surge in new members since Jeremy Corbyn’s Your Party collapsed due to infighting, raising fears that the hard left without a home are joining the party en masse, and altering its culture.

Writing in on Friday, former leader Caroline Lucas said the party’s internal structures left it “woefully exposed” to “entryism” – the takeover of a party through mass membership.

Entryism is a political strategy which was pioneered by the Marxist revolutionary Leon Trotsky in the 1930s where members of a smaller group join a larger, more established organisation to expand their influence and alter its policies. It has been deployed on the hard left and the hard right in recent years.

Lubna Speitan, a former supporter of Corbyn’s Your Party who put forward the Zionism motion, told she switched her allegiance to the Greens to “prepare the ground somewhere else so at least there’s a foundation built and ready”.

Deputy Leader Mothin Ali, for example, was a Labour member until 2020, leaving after Corbyn resigned. He publicly backed the controversial motion.

Kieran Dams, a councillor in Merseyside who resigned this week, told he expects Polanski to be replaced by someone “much more radical” following a leadership election.

A host of Green grandees, including former leaders Lucas and Jonathan Bartley, and peers Jenny Jones and Natalie Bennett, have called on Polanski to now “show leadership” and undo the recent damage.

Lucas – who holds the accolade of being the party’s very first MP – refused to back Polanski staying in post while insiders told The i Paper there was “growing frustration” over the leader and called on him to “show leadership” and overturn the motion, which has triggered accusations of antisemitism.

The chair of the Jewish Greens has gone as far as calling for Polanski’s resignation after he failed to vote on the motion, agreeing it was a “dereliction of duty”.

Bartley told there was now “toxicity” surrounding the party’s brand and that allegations of antisemitism were “clearly having an impact” on its support. 

Senior figures are largely united in believing Polanski had failed to show leadership by missing the crucial conference vote which endorsed a policy effectively calling for Israel to be abolished and replaced with a single Palestinian state.

Several also told The i Paper Polanski now had to find a way to effectively overturn the motion.

A Green source said the party must move away from the “abstract” debate of whether Zionism is racism and towards “bread and butter” policies around the cost of living, food shortages and rent controls.

They said there must be “a real redoubling of effort to talk about stuff that matters immediately to people”, adding that the Zionism controversy is currently “occupying a space” that should be taken up with core environmental and economic policies.

The source said the situation has put “rocket boosters” on internal discussions around reforming the party’s democratic process. This could involve moving away from the current situation where any card-carrying member can vote on a motion, to a delegate-based system where local branches elect a representative to vote on policy.

Lucas said Polanski “should have been there and he should have voted” while ex-co-leader Adrian Ramsay has called for the party to get “back on track” and return to its “core purpose” of championing environmental causes.

A Green Party source told The i Paper there was “growing frustration with Zack having been missing in action for this crucial conference vote, and his attempts to sweep the issue under the carpet are not going to work”.

“Most senior Greens recognise the situation is not tenable and the question will be whether Zack engages with this and shows leadership on finding a way forward for the party,” the source said.

“On the programme he said that he does not agree with the motion. Question is what is he going to do about it?”

The source added that Polanski was now in danger of having “extremists calling him a Zionist”, which puts him “in danger of losing the confidence of both wings”.

They also questioned his performance in the by-election, saying his vote share was similar to the combined 2024 general election figure for the Greens and a Gaza independent, who later endorsed Polanski in the seat.

Vivien Lichtenstein, chair of the Jewish Greens, said Polanski had not worked with her group before the vote, adding on Times Radio: “I think he should resign.”

Polanski now urged to show leadership

Other senior figures backed Polanski to continue if he can address the controversy surrounding the motion and reform the party.

Ellie Chowns, leader of the Greens in the Commons, told The i Paper: “You win some, you lose some in politics. So this by-election doesn’t have to be the end of Zack’s political career, not at all. There probably aren’t that many MPs who have never lost an election.”

Chowns opposed the Zionism is racism motion and said she “would like to have seen an equally clear position from Zack against that motion”.

“I do think that now we have to recognise that although the party tends to pride itself on its member-led democratic decision-making process, actually having just 0.4 per cent of your members decide on a policy that is in my view contrary to Green values and contrary to the views of the majority of Green members is not a sustainable position to be in.”

“I do want to reverse that particular policy, but it highlights a wider issue.”

“That leadership is needed in the party and I very much hope Zack shows that leadership.”

Baroness Jones told The i Paper the Zionism motion was a “clumsy attempt to do what various members thought was the right thing”, adding that she “would have voted against it”.

She also said Polanski must now show leadership in handling the controversy, adding: “I think definitely the fact there is some division on how to think about this motion and how to deal with it and what to do with it next, I think it is for him to be involved in that process.”

Jones added: “He hasn’t lost my confidence. I can’t claim to speak for loads of people, but I think most of us want it sorted, and to see Zack in the hurly-burly sorting it is something we want to see.”

Baroness Bennett said she “absolutely” retained confidence in Polanski, but added that she was “really disappointed” to see Jewish Greens leaving the party after the motion passed.

She urged Polanski to provide “reassurance” to members that there is “no discrimination against anyone in the party, whether they go to a synagogue, belong to a community group, or any other organisation”.

‘Many of us were persuaded not to campaign’

Siân Berry, another Green MP and leading figure, said senior figures had been persuaded not to publicy fight the motion for the sake of the by-election campaign. Writing on Instagram she said:  “The clash of conference with an exciting and mobilising by-election campaign meant many of us were persuaded not to campaign publicly for these ends”.

“I want to take my full share of personal responsibility for the result of all this in the votes at conference. I should have worked harder to persuade more of our leading figures to speak up in a unified way.”

Polanski defended his decision to miss the conference vote on the anti-Zionism motion because he was campaigning in the by-election.

Asked if he supported the motion, he said: “I would have supported the motion as amended. It wasn’t amended, so no.”

He added: “Ultimately, I agree with the substance of the motion. Where I disagree is the idea the Green Party should be deciding what the future of the region looks like.”

On BBC Radio 4’s programme Polanski, who is Jewish, repeatedly refused to say whether Israel had a right to exist.

“I believe Israelis and Palestinians should have equal rights in a democracy,” he said.

Polanski was defeated in the Holborn by-election by Camden Council leader Sagal Abdi-Wali, who retained the north London seat for Labour.

She secured 45 per cent of the vote to the Greens’ 33 per cent, a majority of 3,364.

Holborn and St Pancras has been a Labour stronghold since its formation in 1983, held by Frank Dobson for 32 years and Starmer for 11.

Polanski remains defiant, insisting “of course I can carry on [as leader]” while acknowledging that Green members would ultimately decide his face.