The Green machine: Zack Polanski is remaking British politics from the left. Can he make it last?

Jeremy Adu-Poku

London, UK

Image: Bristol Green Party / Wikimedia Commons / CC0 1.0.

In the taxonomy of British political insurgencies, the Green Party has long occupied an awkward position — too radical for the suburbs, too bourgeois for the north, too small to matter. That description is now obsolete. With local elections on May 7th, the party enters its most consequential electoral test ever, and does so from a position of extraordinary momentum.

The numbers are striking. Since Zack Polanski became leader in September 2025, the party's membership has more than tripled, reaching 225,000 by April 2026 — surpassing both the Liberal Democrats and the Conservatives. The Young Greens have grown to 50,000 members, making them Europe's largest party youth wing. By late March 2026, the Greens had overtaken both Labour and the Conservatives in the aggregate of national polls — the first time ever the top two parties in British polling were neither the governing party nor the official opposition. This is not a protest. It is a structural realignment.

Polanski himself is a peculiar sort of political phenomenon. Born David Paulden in Salford in 1982, he studied drama at Aberystwyth, trained at an Atlanta drama school, and worked variously as an actor, a school activity provider, and a hypnotherapist before entering politics. He joined the Liberal Democrats in 2015 before defecting to the Greens in 2017. He was elected to the London Assembly in 2021. He won the party leadership in September 2025 with 84.1% of the vote — the first time an incumbent Green leader had ever been defeated in a leadership contest.

What distinguishes Polanski from his predecessors is his deliberate repositioning of environmentalism as a class issue rather than a lifestyle choice. He describes his politics as "eco-populist," arguing that people cannot engage with the climate crisis while struggling with rent, food costs, and stagnant wages. The framing is cannily chosen: it lets him contest Reform's terrain (working-class economic anxiety) while retaining the educated urban base the Greens have long relied upon. He has advocated taxing extreme wealth rather than ordinary income, renationalising water companies, and tightly regulating large multinationals. Internationally, he has been compared to Zohran Mamdani, the leftist who won the New York City Democratic mayoral primary — a politician who ran on free childcare, free transit, and affordable housing. The parallel is instructive, and intentional.

Labour's collapse has provided the opening. In December 2025, Polanski held an approval rating of –1, compared to Keir Starmer's –43 — a chasm that speaks less to Polanski's strengths than to the scale of Starmer's alienation of the left. The Gorton and Denton by-election in February 2026 crystallised the shift: Green candidate Hannah Spencer won with 41% of the vote and a majority of more than 4,000, with Labour falling to third. This was not a freak result. It was a signal.

The May elections now represent a chance to convert polling into power. Projections are remarkable. One model from the Elections Centre forecasts the Greens finishing with nearly five times the number of seats they began with. Others project net gains of around 555 council seats nationally, from a base of 141. In London, some models show the Greens winning more seats than any other party, with Labour projected to lose 741 seats — potentially losing control of Hackney, Lambeth, and even Camden, home to Keir Starmer's own constituency. In the West Midlands, YouGov's MRP has Greens polling 18% — level with the Conservatives and behind only Labour.

Yet the risks are real. Polanski's politics carry several vulnerabilities. His stated desire for Britain to eventually withdraw from NATO sits awkwardly in the current European security environment. His 2026 remarks claiming antisemitism accusations were "weaponised" against Jeremy Corbyn will unsettle Jewish voters and centrists alike. And the party still lacks the local government infrastructure to convert surging polls into durable administration across dozens of councils simultaneously.

There is also the question of durability. Membership explosions and poll surges have flattered British insurgent parties before, only to recede when governing reality intrudes. What is different this time is the depth of the Labour collapse and the coherence of Polanski's positioning. He has found a register — angry, specific, economically credible — that reaches beyond the usual Green demographic. Whether he can hold it together after May, when the hard work of council chambers and budget constraints begins, is another matter entirely.

For now, the Green machine is running. Britain's political map is about to look very different.