UK Green Party leader Zack Polanski has vowed to stay on despite losing the by-election for Holborn and St Pancras.

Labour’s Sagal Abdi-Wali held the seat. The by-election was triggered when former prime minister Keir Starmer stepped down last month.

Polanski faced calls to resign. Vivien Lichtenstein, leader of the Jewish Greens, said his leadership was a ‘big mistake’. She criticized him for dodging a debate over a party conference motion that described Zionism as a form of racism.

Polanski said he would remain leader. The Greens are trying to build on recent gains in local elections.

The by-election was seen as an early test of the political landscape after Starmer’s departure. Labour will be relieved to hold a seat it could not afford to lose.

The seat had been held by Labour for decades. Starmer’s resignation forced a contest neither side wanted this soon.

The Greens had hoped to make gains. Instead, Labour held on, and the result has sharpened questions about Polanski’s leadership.