Zack Polanski failed to show leadership over a motion passed by Green Party members declaring Zionism a form of racism, the party’s former leader Caroline Lucas has told the BBC.

Lucas told Newsnight that the party’s current leader, who did not attend the debate on the motion at the Green Party’s annual conference in Brighton, “should have been there and he should have voted”.

She described the motion, which defined Zionism as an ideology supporting “an ethnonationalist Jewish state”, as “dangerous” and “divisive”.

In the wake of the vote, Polanski has said he will not accept anyone being excluded from the Green Party “because of the religious or communal body they are part of”.

Lucas’s comments came after polls closed in the Holborn and St Pancras by-election, where Polanski is standing as a candidate.

Polanski did not vote on the motion after leaving the party’s conference early to campaign in the north London constituency.

The Green leader has declined media interviews since the motion was passed on Sunday and did not answer questions from a BBC reporter about the motion earlier on Thursday.

The motion also backed a “single democratic Palestinian state in all of historic Palestine”, which includes modern-day Israel.

Under Green Party rules, motions supported by members become official party policy, but will not necessarily be included in the party’s manifesto at the next general election.

Lucas, who voted against the motion, said: “I would have hoped [Polanski] would have been a very strong critic of this motion.”

She added that it was “flawed from top to bottom”.

Asked if Polanski should stand down, she told Newsnight: “I think let’s just see what happens in the coming days and weeks. Obviously he has been completely taken up with this by-election.

“I want him to speak now about what’s happened, I want him to show the leadership that was frankly missing on Sunday.

“I think the jury is out about whether he will do that – but I very much hope he will.”

In response to Lucas’s comments, a Green Party source said: “There are ups and downs in politics and when people are passionate they disagree in the heat of a campaign.

“We do things differently – unlike Labour who use anonymous sources and resort to factionalism.”

The motion has overshadowed the final days of Polanski’s by-election campaign, where the Greens have been looking to overturn a substantial Labour majority in the seat vacated by former Prime Minister Sir Keir Starmer.

It has sparked days of controversy and exposed divisions between the party’s newly enlarged membership base under Polanski and its MPs elected at the last general election.

Four of the five Green MPs opposed the motion, while the party’s co-deputy leaders were split over whether they supported it.

The vote also led to the resignation of the Green deputy leader in Wales and condemnation from the European Green Party.

In a written statement on Monday, Polanski did not specify whether he supported the motion passed by members but sought to reassure Jewish members that “no-one will be made unwelcome because of their background, their faith, or where they worship”.

Polanski, who is Jewish, added that “antisemitism and criticism of the Israeli state are, and must always be, completely distinct”.

Ahead of the vote, he had backed an amendment to specify that the motion should not be used to discipline Jewish members attending synagogues that consider themselves Zionist, but this was voted down by members.

He had also said he wanted to see the reference to a single Palestinian state changed, arguing: “I don’t believe we as a Green Party of England and Wales, or even the British government, should be deciding what the future settlement looks like.”

Meanwhile, Prime Minister Andy Burnham has called on Polanski to reverse the motion and ensure it is not Green Party policy.

In his first comment on the row, Burnham said it was “completely wrong” for the party to support the motion and this showed “terrible judgement”.

The PM said he felt the motion effectively ruled out a two-state solution between Israel and Palestine.

“For that reason, it shouldn’t be supported in any way, shape or form,” he told reporters while on a visit to Berlin.

When asked if he would rule out entering into coalition with the Greens, he would not be drawn on “any business about what might or might not happen in the future”.

On Thursday, a Green Party spokesperson said: “This has been an emotive issue and is complex. It has rightly caused much discussion, and needs to be taken in the context that Israel’s behaviour has had.

“Israel has been responsible for a genocide, ethnic cleansing and the killing of children, and we’ve had a political establishment which has not only turned a blind eye but provided support.”

The International Court of Justice (ICJ) is currently hearing a case brought by South Africa that accuses Israeli forces of genocide, but it could take years to reach a conclusion. Israel has called the case “wholly unfounded” and based on “biased and false claims”.

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