Green Party members have adopted a motion declaring Zionism a form of racism, in a move that has divided senior figures at the top of the party.

The party’s two deputy leaders have been at odds over the subject, with Mothin Ali backing the move, and Rachel Millward describing the wording as “problematic”.

Activists endorsed the policy motion, which was put forward by a group of members at the party’s conference in Brighton, by 1022 votes to 813.

They also voted to commit the party to supporting a “single democratic Palestinian State”, after they rejected an amendment that had been backed by party leader Zack Polanski.

The motion adopted by Green members defines Zionism as an ideology in support of “an ethnonationalist Jewish state” and backs a “single democratic Palestinian state in all of historic Palestine”.

“The real, material, manifestation of Zionism has been the historic and ongoing dehumanisation, displacement, dispossession, disenfranchisement and destruction of Palestinians,” it says.

It has attracted criticism from some Jewish groups, including the Board of Deputies and the Jewish Leadership Council.

In a letter to the party sent ahead of the vote, the organisations said Zionism was an anti-racist movement, adding that “modern Zionism was formed in part as a response to antisemitism, creating a refuge for Jews in their ancient homeland after millennia of persecution outside it.”

It also raised concerns about the safety of Jewish members in the Green Party, as well as the implications for Jewish institutions in areas represented by the Greens.

Debate about the motion, as well as the conflict in Gaza, has featured heavily during the conference, which is taking place after a surge in its membership following Polanski’s election as leader last year.

On Friday, Polanski said he believed Zionism, as it was defined in the motion, was racism.

However, he 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.”

He had also said he wanted to see the motion amended to specify that it should not be used to discipline Jewish members attending synagogues that consider themselves Zionist.

However, both amendments favoured by Polanski were rejected by Green members.

A Green spokeswoman insisted the party would protect Jewish members – and they would not be persecuted for attending synagogues which defined themselves as Zionist.

Polanski himself did not vote in the debate, having left the conference early to campaign in Holborn and St Pancras, where he is standing to be the MP. A full list of candidates can be found here.

Over the course of the three-day conference, key figures in the party have expressed differing positions about the Zionism motion.

Three of the party’s five MPs – Ellie Chowns, Adrian Ramsay and Carla Denyer – had publicly opposed it, with Denyer arguing it could risk “alienating a significant proportion of Jewish people”.

On Friday, former leader Caroline Lucas told the BBC: “I think there is no single definition of Zionism and, irrespective of the intentions of those who put that motion, I think there is a real risk that it will be divisive and could be seen as a sign that Jewish people aren’t welcome in the party.”

Deputy leader Mothin Ali, who had expressed support for the motion before the vote, said it was calling for “a state that’s democratic, that guarantees the rights of every single person living on that land”.

He added that he was “absolutely not” calling all Jewish people who define themselves as Zionists racist.

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.

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