Zack Polanski has acknowledged that he is the “underdog” in the Holborn and St Pancras by-election but insisted that the Green Party can defy expectations and take the safe Labour seat vacated by the former Prime Minister.

The Green Party leader rejected suggestions that his party has reached the limits of its recent surge in popularity and said he hopes to pull off “one of the biggest upsets in British political history”.

This is despite a YouGov survey this week suggested the Greens would win zero MPs in the capital if a general election was held tomorrow amid a “Burnham bounce” for Labour across the country.

But Mr Polanski pointed to his party’s performance at the 2024 general election and council polls held in May.

The London Assembly member told the Standard: “Those same polls said that we weren’t going to do very well at the general election.

“In 2024, we went on to win all four of our target seats. We then, of course, earlier this year in February in Gorton and Denton won our fifth MP, Hannah Spencer, despite polls, journalists, commentators, everyone saying we can’t do it.

“And you know what? In Holborn & St. Pancras...I intend to win.”

The Greens won four parliamentary seats at the 2024 election - Bristol Central, North Herefordshire, Waveney Valley and Brighton Pavilion.

The party subsequently gained a fifth MP through a by-election victory in Gorton and Denton earlier this year.

At the council elections in May, the Greens made sweeping gains in London at the expense of Labour.

Six town halls in the capital are now under the party’s control.

But Holborn and St Pancras has been represented by Labour since 1983. Sir Keir Starmer won a majority of more than 11,500 votes there in 2024.

Mr Polanski’s main rival is Labour’s Sagal Abdi-Wali. She is the leader of Camden council who came to Britain from Somalia as a child refugee and has promoted her strong links to the community across the constituency.

The upcoming by-election is viewed as a significant test of whether the Greens can translate their national support into another Westminster breakthrough and whether Mr Polanski’s momentum can extend beyond his party’s existing parliamentary strongholds.

Asked directly whether he accepted that he is the underdog, Mr Polanski said: “Oh, without a doubt.

“It’s been a supposedly safe seat since 1983. They have a Labour council, a Labour mayor of London and the Labour government.

“But what I’m hearing on thousands of doorsteps over and over again are people recognising that Labour have tired, old ideas that aren’t really meeting this moment, the cost of housing, whether it’s renters whose rents are going up and they badly need rent controls or leaseholders where this Labour government said they would end the feudal system of leasehold but haven’t taken the action.

“And so, although I’m the underdog, I’m feeling pretty confident, although not complacent. I’m going to be campaigning for every single vote.”

The Greens are holding their annual political conference just days before the by-election on October 8, which would usually mean activists, campaigners, MPs and councillors holed up in Brighton deciding on party policy.

But Mr Polanski has said he will not be attending the full meeting of members between October 2 and 4.

He has urged activist to skip the conference as well to help him campaign, offering refunds and online voting to those who have already paid for their spot.

“I won't be in Brighton for very long because I want to win an election,” he said.

“And what I would say to every activist in the Green Party is I love Green Party Conference, I have not missed one in the last nine years.

“But this is a historic by-election because it's not just about this seat, although first and foremost it's about the people in Holborn & St. Pancras, but it's about winning big in London in the next few years.

“It's about winning big at the next general election. And if we win this election, if we cause one of the biggest upsets in British political history, then that will change the future of British politics.”