GREEN Party leader Zack Polanski has confirmed he is looking to fight the Holborn and St Pancras by-election in the first major political challenge to new premier Andy Burnham.

His candidacy — which requires endorsement by local party members — will put pressure on Mr Burnham from the left as he struggles with City demands to abandon his ambitions to reverse neoliberalism.

Mr Polanski immediately slammed Labour as the party for big business and big money, the interests trying to dominate the new government.

The move turns the poll in the north London seat — caused by the resignation from the Commons of Keir Starmer, promises to the contrary notwithstanding — from an expected easy win for Labour into a real political fight.

Mr Polanski received immediate personal backing from independent pro-Palestine campaigner Andrew Feinstein, who slashed Sir Keir’s majority in the 2024 general election.

Mr Polanski told the local newspaper in Camden, the borough in which the constituency sits: “Holborn and St Pancras has everything that’s the best of our country and so much potential.

“But for too long now it’s been held back by governments who have failed to make the changes to improve people’s lives.

“We know that the Greens can win here, and by electing me, voters will have someone who will always fight their corner — never scared of big donors or the party whip. Too often Labour has stood up for corporations and big money. I will stand up for people struggling to pay their bills.”

He added that he would campaign on “making life more affordable,” adding “this is a chance to send a very clear message that we won’t sit by as we get poorer and extreme wealth is concentrated at the very top.”

Mr Polanski seems certain to be preferred by Greens in Camden, although some local activists are sceptical about his candidacy and would rather nominate a community campaigner. He had hitherto appeared focused on winning a seat in Hackney, where the Greens run the local authority, at the next election.

The Green leader is gambling that his high-profile campaign can help reverse the slide in the polls the party has experienced since Mr Burnham became Prime Minister.

The vote will also test whether the “Burnham bounce,” muted as it is, can help Labour reunite the progressive coalition scattered to the winds by Sir Keir’s failed leadership.

Mr Polanski won important backing from Mr Feinstein today. The former ANC MP in South Africa said he personally welcomed news of Mr Polanski standing: “Zack will be an excellent candidate. Unfortunately I am not in a position to stand this time round.

“The Camden People’s Alliance, the community group created out of my campaign against Starmer, will meet next week to formally decide our position. This is a crucial time for progressives in Camden and across the country to be united,” he said.

Mr Feinstein and the Green candidate secured almost 30 per cent of the vote in the seat in 2024 between them.

Labour has yet to name its candidate to replace Sir Keir, but the frontrunner appears to be Camden council leader Sagal Abdi-Wali, who has Somalian heritage.

She is identified with the right in the local party and is seen as a protege of Sir Keir.  She has not, for example, spoken out on the crisis in Gaza.

Elections specialist Rob Ford said Mr Polanski’s move meant “big stakes now for both parties.

“Greens have a chance to turn the tide on recent decline and show Polanski is a winner. Labour have a chance to show the Burnham bounce is real, consolidate the left in a London heartland seat, and deal a potential knockout blow to Green insurgency.”

The now turbo-charged contest comes against the background of unrelenting pressure on the new government from the money markets, which are bidding up the price of government debt in advance of Chancellor John Healey’s Budget next month.

The aim is to box Mr Burnham into a corner, mandating spending cuts on everything except the military.

Senior Labour MP Emily Thornberry, however, spoke up for tax increases as an alternative today.

She said she thought “we’re going to need to raise taxes” because of the “huge strains on the economy” and claimed that “people will understand.”

The Resolution Foundation think tank also backed higher taxes, arguing that Britain is a relatively low-tax country by global standards.