Pressure is growing on Zack Polanski after his by-election defeat, with Green leaders and insiders in London critical of the party’s direction.

Senior Green figures in London have attempted to put clear water between them and the party conference’s “Zionism is racism” motion that has caused infighting.

Mr Polanski, the Green Party leader, lost last week’s by-election in Holborn and St Pancras to Labour – a contest triggered after former prime minister Sir Keir Starmer resigned as an MP.

The Green vote rose by 22% compared with the general election result in 2024, but Mr Polanski was still 12 points behind his Labour rival, Sagal Abdi-Wali.

The result came just days after members at the Green Party conference in Brighton voted in favour of declaring that Zionism, the movement that led to the creation of the state of Israel, amounts to racism.

In the aftermath of the by-election loss, Vivien Lichtenstein, chair of Jewish Greens, called for Mr Polanski – who is Jewish and opted not to vote on the motion – to resign.

Four out of five of elected Green MPs have said they did not support the position. Mr Polanski, who has vowed to stay on as leader, has since indicated that he would not have backed the motion’s wording.

In north London, the Green leader of Haringey Council has announced that he did not support the national party’s “unhelpful” motion on Zionism.

Mark Blake said that, while he respected some of its “core principles”, he did not think it was a UK political party’s place to apply solutions in place of the Israeli and Palestinian people.

As well as defining Zionism as racism, the motion also called for a “single democratic Palestinian state in all of historic Palestine”. Both the UK government and UN advocate for a two-state solution to the Israel-Palestine conflict.

In a statement, Mr Blake said: “I support the core principles of the policy: no state should be established on the idea that one religion is superior to another.

“The political ideology behind the displacement and genocide of the Palestinian people is clearly racist.

“However, I don’t feel comfortable with British political parties or politicians deciding on behalf of Israelis and Palestinians what the solutions should be.”

The councillor for Tottenham Central, who became Haringey leader after the local elections in May, said he felt it was “unhelpful to focus on an ideological debate on definitions”, rather than create “ideas to establish a just peace for all”.

Internally, the post-mortem over Holborn and St Pancras is continuing, with party sources critical of both the style of the campaign and the decision to allow the controversial Zionism motion at the party conference on the weekend before the polls opened.

Green, Labour and Liberal Democrat sources claim that some Conservative and Lib Dem residents had voted tactically for Labour to block Mr Polanski from becoming their MP.

Activists privately complained that the by-election campaign focused heavily on Mr Polanski and not enough on constituency matters.

“There’s nothing about local issues,” said one activist who spoke anonymously to the Local Democracy Reporting Service. “We needed to be holding Labour to account for their record here in Camden,” the activist added.

Mayor of Hackney Zoe Garbett, who won the borough for the Greens in a historic first in May, was another council leader who did not vote on the divisive Zionism motion.

That was reportedly because she was instead campaigning for Mr Polanski in Holborn and St Pancras.

A spokesman from her office laid out Ms Garbett’s position in a statement that said: “If Zionism is defined as a political ideology supporting the creation and continuation of a specific ethnonationalist state in historic Palestine, born from colonial actions and enabled through ethnic cleansing, then it is racist.”

A Green source in Hackney, however, said Ms Garbett was privately “really frustrated” the debate was sapping time and energy away from local matters.

Garbett, who was elected as councillor for Dalston in 2022, is “not ideological”, the anonymous local party member added.

“Regardless of what she believes about Zionism, I don’t think she would support the motion because it devotes energy to something definitional. She is much more ‘build bridges, not walls’.”

In Hackney, the issue of Israel-Palestine will soon rear its head again due to the Greens’ manifesto commitment to de-twin the borough from Haifa in Israel.

A majority of councillors in the east London borough voted in July to trigger a consultation over whether the borough should “formally terminate” municipal ties with the Israeli port city.

Mayor Garbett said maintaining the link was “fundamentally at odds” with Hackney’s anti-racist values after a UN Commission of Inquiry report said Israel had committed genocide in Gaza. More than 70,000 Palestinians are reported to have been killed since the conflict with Israel reignited three years ago.

The consultation over de-twinning ends on October 14. The initial deadline of October 7 was pushed back amid accusations of “shocking insensitivity” from Jewish groups due to it being the anniversary of the Hamas terrorist attack on Israel. Ms Garbett later apologised to the Mayor of Haifa for the “serious error”.

One Green insider said he felt the party had “opened a can of worms” by floating the de-twinning policy so soon after winning control of the town council in May.

He said: “We’re paying a price. The question is - was it worth it?”.