One in three Britons think Zack Polanski should resign as the leader of the Green Party, polling conducted on Friday in the wake of his defeat in a key Parliamentary by-election has found.

Just one in five (20 per cent) think he should remain in post amid widespread condemnation of a party motion that declared Zionism to be a form of racism, according to the YouGov survey.

Mr Polanski is facing growing calls from within his party to stand down, with one senior Green figure telling that the situation is “untenable”.

The leader of the Jewish Greens, Vivien Lichtenstein, has called for him to resign and said he made a “big mistake” by missing the debate on the motion last week.

She is among a number of senior Green figures to have publicly criticised Mr Polanski and raised concerns about whether he should continue to lead the party, with former leader Caroline Lucas accusing him of a failure of leadership.

On Friday, he said he would have voted against the ‘Zionism is racism’ motion - but was too busy campaigning in the by-election.

He told the BBC he would have tried to amend it on two grounds. But “those amendments fell, and so I would have voted against the motion because I think there are aspects of it that I don't think are okay.”

The motion has been widely condemned, with the chief rabbi, Sir Ephraim Mirvis, describing it as a "threat to British Jews and to Britain".

Leading barrister Adam Wagner KC also said there was a strong risk the motion, passed at the Greens’ annual conference last weekend, contravenes the Equality Act 2010, while Mr Polanski has been barred from entering Israel in retaliation.

Mr Polanski was defeated in the race to replace Sir Keir Starmer as the MP for Holborn and St Pancras by Labour’s Sagal Abdi-Wali.

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

The YouGov poll asked “Do you think Zack Polanski should remain as leader of the Green Party, or stand down and let someone else take over?”

Overall, 47 per cent said they don’t know.

Green voters tended to back their leader, with 47 per cent of those who voted Green in 2024 saying he should remain, while 22 per cent think he should stand down.

Labour and Lib Dem voters are divided on the issue, with 29 per cent feeling he should stay leader and 29-33 per cent wanting him to stand down.

The Greens have been approached for comment.