Who is Zack Polanski, the ‘eco-populist’ rattling the UK’s establishment?

By Issy Ronald, CNN

London (CNN) — The leader of the UK’s Green Party, Zack Polanski, will on Thursday challenge the political establishment by taking on the ruling Labour Party in a special election for the seat held by former prime minister Keir Starmer.

Polanski, with his deep reserve of progressive policies and an active presence on TikTok cuts a markedly different figure to Starmer, who consistently alienated his Labour Party’s left-wing and developed a reputation as a stilted, ineffective communicator.

That contrast helped Polanski and the Greens gain traction as a popular left-wing alternative to the governing, center-left Labour Party, which has been bleeding voters in recent years over its stance on issues like welfare spending, trans rights and the war in Gaza. Polanski even said on more than one occasion that his party “is here to replace Labour.”

But that momentum has largely stalled since Starmer resigned as prime minister in the summer following enormous pressure from his party. He stepped down as a member of parliament (MP) last month, triggering the by-election.

In Starmer’s place, a more formidable opponent has emerged. Andy Burnham, the current prime minister, is widely seen as a better political operator and more capable of appealing to a broad spectrum of voters, including the progressives Polanski has been targeting.

So the outcome of this by-election – in the central London constituency of Holborn and St. Pancras – represents more than just Polanski potentially becoming an MP.

It pits the Greens and Labour directly against each other for the first time since Burnham took office, acting as the first major electoral test for the new government as well as a barometer of the Greens’ ability to compete with a rejuvenated Labour.

If Polanski wins on Thursday, it will be a stern warning for the new prime minister and could be an early indicator that Britain’s left flank has irrevocably split. But if he loses and Labour candidate Sagal Abdi-Wali holds the party’s seat, it will serve as a sign that Burnham has managed to pull progressives back into the Labour Party and slow its electoral decline.

Differing stances over the war in Gaza and antisemitism are central to that split, and to this by-election. Many Muslim voters have said they will not vote Labour because they think the government has not acted strongly enough over Gaza.

This weekend, the Greens adopted a controversial motion classifying Zionism, which Jewish groups sometimes define as a right to Jewish self-determination, as a form of racism, calling it an “ethnonationalist political project.”

Polanski, who is Jewish and changed his name from David Paulden when he was 18 to honor that heritage, did not vote on the motion nor mention it in his speech to the conference. He describes himself as an “anti-Zionist.” Israel responded by banning Polanski from visiting the country.

On Wednesday, a fresh storm broke out in British media over a reported friendship between the Green Party member who proposed the motion and a man convicted in the United States on al Qaeda terrorism charges.

Any split in the left comes at a critical moment in British politics, with Labour (and the Greens) also focused on containing a rising right-wing wave, most clearly signaled by the rapid ascent of the hard-right populist party, Reform UK.

Who is Polanski?

A self-described “eco-populist,” Polanski, 43, was catapulted onto the national stage last fall when he secured a surprise victory in the Greens’ leadership election, beating two of the party’s four MPs to claim the top job. Before that, he was still a little-known local politician, representing the Greens in the London Assembly.

The broad brushstrokes of Polanski’s image go something like this: to his admirers, he is an antidote to the stiff technocratic tendencies of more mainstream politicians; a gifted communicator willing to adopt the bold left-wing policies Labour has largely shied away from.

To his detractors, he is vague and unable to pin down the details of his own policies.

More recently, his social media use sparked controversy after he criticized the police’s response to an antisemitic attack in north London and, in a separate incident, reposted a photo that some interpreted as threatening Nigel Farage, the leader of Reform UK.

Still, under his leadership, the party has commanded national attention, building on its best general election performance when it secured four parliamentary seats in 2024. By May, the Greens’ rise seemed astronomic – they briefly polled as high as Labour and the center-right Conservatives, the two parties which have dominated British politics for decades, and enjoyed historic gains in spring local elections.

While Polanski has tried to link the climate crisis to other issues, he has largely prioritized immediate everyday concerns, such as the cost of living and suggestions of public ownership of water and other utilities, alongside other progressive initiatives like championing a wealth tax and rent controls, while also adopting a pro-Palestinian stance.

Polanski has claimed credit for pushing Labour further to the left, most recently saying his party was responsible for influencing Labour’s shifting stance on the Middle East, including the government’s recently announced sanctions on illegal Israeli settlements in the occupied West Bank.

Actor turned politician

A former actor, Polanski’s strength lies in his communication. He hosts his own nightclub nights and holds weekly conversations with academics, activists and journalists on his podcast “Bold Politics” on ideas like an extreme wealth line (a proposed globally agreed limit for an individual’s net worth), re-nationalizing water companies and rejoining the European Union.

But he is prone to slip-ups too – in one disastrous interview shortly after becoming leader he seemed to confuse the national debt and deficit. Months later, he more carefully laid out his economic policy at a left-wing think tank event, though it remains “vague,” said Laura Serra, a political scientist at the London School of Economics.

“People don’t really know what they (the Greens) stand for, what they’re going to do,” she added.

While Polanski’s almost constant media presence has given him a far higher profile than previous Green leaders, analysts argue that the party’s increasing popularity has less to do with him and more to do with the shifting political climate in the UK.

And at the same time, Green parties across Europe have become more influential, propelled by growing support among recent graduates and benefiting from “changing societal cleavages,” said James Dennison, a political scientist at the European University in Florence, who has studied the Greens for more than a decade. “The change is more rapid in the UK, and it’s exaggerated partially because of the electoral system, so it takes them longer to break through, and when they do, they go faster.”

Polanski self-consciously forms part of a wider populist trend too; he describes his approach to messaging as “substance with clickbait” and an alternative designed directly to confront the right-wing populism of Reform, and its Trump-supporting leader Nigel Farage.

“Populism is about the 99%, the vast majority… against the very, very wealthy… Trump and Farage come from the 1% and want to protect the interests of the elite,” Polanski told Bloomberg earlier this year.

This simultaneous rise of the Greens and Reform could fracture Britain’s political landscape, in which the first-past-the-post electoral system typically favors two or three major parties.

So, regardless of who wins on Thursday, the Greens even being competitive in a traditional Labour stronghold like this is indicative of how the smaller, more radical parties are increasingly challenging the mainstream.

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