Senior figures within the Green Party have expressed private concerns that leader Zack Polanski may have reached the peak of his political momentum ahead of the Holborn & St Pancras by-election. Polanski, who assumed leadership last year, has significantly increased party membership and polling figures but faces doubts within the party about translating this surge into active grassroots support on the ground.

The by-election, triggered by Sir Keir Starmer’s resignation as an MP, has become a critical test for Polanski and the Green Party. While the party has previously seen a boost in membership and electoral success, some insiders question whether this enthusiasm will hold in the face of changing national political dynamics, particularly with Andy Burnham now serving as prime minister. One party insider noted skepticism about whether voters drawn to the Greens during Starmer’s leadership will maintain their support under Burnham, adding that this concern extends beyond the by-election to potential general election prospects.

Although party leadership did not expect an outright win in the seat—long considered a Labour stronghold—there was hope the contest could be competitive. The Greens secured about 10 percent of the vote in Holborn & St Pancras at the 2024 general election, while an independent candidate with a strong stance on Gaza captured nearly 19 percent. Labour retained the seat in that election. Polanski acknowledged the Greens were "underdogs" upon his selection but maintained that the party had momentum.

Polanski’s campaign has faced significant challenges, including a fraught hustings event held last Thursday by the Board of Deputies of British Jews and the London Jewish Forum. At this event, Polanski was heckled and booed after describing himself as "anti-Zionist" and when questioned about his positions on Israel, Gaza, and antisemitism. Those close to the campaign described the meeting as "traumatic" and emphasized the need for party members to rally around Polanski in its aftermath.

In a private messaging group for activists working on the campaign, one attendee described the event as difficult and cautioned members about potentially negative media coverage. Campaign manager messages urged supporters to avoid divisive debates on social media and focus instead on door-to-door campaigning. A senior campaigner highlighted the personal risks Polanski has taken for his beliefs and his contributions to the party.

Internal tensions have also emerged over resource allocation for the by-election. Polanski advocated postponing the upcoming Green Party conference to allow activists to concentrate fully on campaigning in Holborn & St Pancras, but the party executive rejected the proposition. Activists have been offered refunds for conference tickets if they choose to campaign instead.

A Green Party spokesperson acknowledged the uphill battle in one of Labour’s safest seats but emphasized that the party’s message on affordable housing, climate change, and holding Labour to account is resonating with voters at the doorstep. The spokesperson said the race remains close and expressed confidence in a potential Green victory.