Zack Polanski insisted he will carry on as Green leader despite failing to win a seat in Parliament as the fallout continued from the party conference backing a motion declaring Zionism is racism.

The Green Party of England and Wales leader’s position was being questioned by senior colleagues even before he was unsuccessful in ousting Labour in the Holborn and St Pancras by-election triggered by the resignation of former prime minister Sir Keir Starmer.

Mr Polanski said “of course I can carry on” as party leader but acknowledged that ultimately Green members would decide his fate.

The party leader missed the crucial conference vote which endorsed a policy effectively calling for Israel to be abolished and replaced with a single Palestinian state.

Former leader Caroline Lucas said Mr Polanski “should have been there and he should have voted” while ex-co-leader Adrian Ramsay has called for the party to get “back on track” and return to its “core purpose” of championing environmental causes.

Mr Polanski said it would be up to Green Party members whether he continues as leader, with a scheduled leadership vote due next year.

Asked how confident he was to be re-elected as leader, he told Sky News: “That’s going to be up to the members and that’s going to be up to the leadership election that happens next summer.

“What I’m experiencing, though, is an immense amount of people who are saying actually they’ve never been prouder to be a Green Party member.”

He said it was “difficult being leader of any party, particularly the Green Party”.

“But I signed up for that difficult job and I’m more than ready to continue,” he added.

He defended his decision to miss the conference vote on the anti-Zionism motion because he was campaigning in the by-election.

Asked if he supported the motion, he said: “I would have supported the motion as amended. It wasn’t amended, so no.”

But he added: “Ultimately, I agree with the substance of the motion. Where I disagree is the idea the Green Party should be deciding what the future of the region looks like.”

On BBC Radio 4’s Today programme Mr Polanski, who is Jewish, repeatedly refused to say whether Israel had a right to exist.

“I believe Israelis and Palestinians should have equal rights in a democracy,” he said.

Asked to give a yes/no response on whether Israel had the right to exist, he added: “At the moment Palestinians don’t have equal rights, so I think I’m answering your question really clearly.”

Mr Polanski was defeated by Camden Council leader Sagal Abdi-Wali, who retained the north London seat for Labour.

She secured 45% of the vote to the Greens’ 33%, a majority of 3,364 but seeing a 13% swing to the Greens, whose vote share was up by 22.4%.

Ms Lucas, who was the Green Party’s first MP, said people should “see what happens in the coming days and weeks” when asked about Mr Polanski’s future on Thursday night’s BBC Newsnight.

She pointed to Mr Polanski’s failure to take part in the controversial anti-Zionism motion on Sunday, saying he “should have been there and he should have voted”.

The adoption of the motion at the party’s conference makes it policy, despite the opposition of Ms Lucas and four of the party’s five MPs, but it does not mean it will necessarily appear in the future manifesto.

Holborn and St Pancras has been a Labour stronghold since its formation in 1983, held by Frank Dobson for 32 years and Sir Keir for 11.

Conservative candidate Ewan Cameron came in third in the by-election, followed by Reform and the Lib Dems.

Ms Abdi-Wali said her victory was a testament to the success of diversity in the borough.

She said: “I hope this moment also says something about who gets to belong, for people who look like me, I hope they see themselves reflected in this place and know that their path too belongs here. This is Camden, and this is Britain.”

She added: “I’ve watched people across Camden work to build communities where difference is not something to fear, but something to value. We cannot allow that work, built over generations, to be casually undone by those who seek to divide us.

“We have a responsibility to defend what we’ve built, and pass it on. Hope is not naive. Without hope there is nothing to build on, and nothing to build for.

“People need to believe that politics can make their lives better and that their communities can thrive and that tomorrow can be better than today.”

She added: “That is what this victory represents. Winning not by making people afraid of each other, but by bringing people together.”