Green Party members in the United Kingdom have voted to adopt a motion declaring Zionism a form of racism, a decision that has exposed deep divisions within the party at its annual conference in Brighton.

Activists endorsed the policy motion, put forward by a group of members, by 1,022 votes to 813. The vote has dominated proceedings at the three-day conference, held following a surge in party membership after Zack Polanski was elected leader in September last year.

The motion defines Zionism as an ideology in support of "an ethnonationalist Jewish state" and backs a "single democratic Palestinian state in all of historic Palestine." It states: "The real, material, manifestation of Zionism has been the historic and ongoing dehumanisation, displacement, dispossession, disenfranchisement and destruction of Palestinians."

The motion was put forward by Green member Lubna Speitan, who said its backers wanted to voice opposition to "racist systems of oppression." Speaking after the vote, she added: "We stand united against all forms of racism and discrimination - no exemptions."

The decision has drawn criticism from Jewish organisations, including the Board of Deputies and the Jewish Leadership Council. In a letter sent to the party ahead of the vote, the two bodies described Zionism as an anti-racist movement, stating 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."

Israel's Foreign Ministry said the motion went beyond "the boundaries of legitimate political debate" and called it "a stain on the history of the United Kingdom."

The vote also raised concerns about the safety of Jewish members within the party and the implications for Jewish institutions in areas represented by Green politicians.

The motion exposed divisions between the party's newly enlarged membership base and its elected MPs. Four of the party's five MPs — Ellie Chowns, Adrian Ramsay, Carla Denyer, and Sian Berry — had publicly opposed it before the vote. Denyer warned it risked "alienating a significant proportion of Jewish people." Chowns and former Green Party leader Caroline Lucas both spoke against the motion during the debate.

Addressing members, Lucas said: "I urge you not to support the over-simplification at the heart of this motion - a refusal to accept complexities which is leading to so many Jewish members" — her remarks were cut off in the available text.

The party's joint deputy leaders were also at odds. Mothin Ali backed the motion, while Rachel Millward described its wording as "problematic."

Polanski did not vote in the debate, having left the conference early to campaign in Holborn and St Pancras, where he is standing as a parliamentary candidate. Asked about the motion, he said: "If your Zionism is the displacement of the Palestinian people then that is clearly racist, and I say that as a Jewish leader of a British political party."

However, Polanski also said he wanted 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 sought an amendment to specify that the motion should not be used to discipline Jewish members who attend synagogues that consider themselves Zionist. Both amendments were rejected by members.

A Green Party spokeswoman said the party would protect Jewish members and that they would not be persecuted for attending synagogues that define themselves as Zionist.

Vivien Lichtenstein, chair of Jewish Greens, said after the vote that she could consider her future in the party.

Polanski did not specify whether he personally supports the adopted motion, but added his name to a joint statement issued by the party's five MPs and deputy leaders following the vote. The statement pledged to ensure the Green Party was "an anti-racist party in every way" and said there was "no conflict between supporting the rights of Palestinians and the rights of Jewish people."