Many metaphors have been used to describe the impressive rise of the Green Party of England and Wales under the leadership of Zack Polanski, from an optimistic ‘green tidal wave’ to a pessimistic ‘green bubble’. However high you think the party can go, one thing is clear after their historic Gorton and Denton victory: the Green Party is now a serious player in British politics.

During the by-election, the Green candidate (and now MP) Hannah Spencer worked brilliantly with the party’s activists to gain 41% of the vote, securing a commanding 4,402 majority. The Green campaign persuaded voters that they were the most viable option to beat Reform, pushing Labour into third place in a seat where they won a 13,413 majority less than two years ago. As Compass said when the result was announced, it was a welcome and uplifting shot of hope.

Ever since Your Party failed to get off the ground as a viable left of Labour political vehicle, and Zack Polanski won a confident victory under the banner of eco-populism in October 2025, the energy of the left has been with the Green Party.

Polanski’s ability to articulate progressive talking points in a hostile media environment quickly drew admiration. He has articulated nuanced positions confidently, condemning antisemitism whilst calling out Israel’s genocide and defending the right to protest. He has been a much needed voice for peace as the drums of war have beaten ever louder.

Under his leadership the Greens have maintained a focus on alleviating the cost of living and tackling inequality. He has called out the racist and dehumanising rhetoric of the far right and positioned the Greens as best placed to take on Reform. All of this has helped to broaden out the party’s appeal which is now being reflected in polling numbers and at the ballot box.

A recent YouGov poll put the party on a record high of 21% nationally, leapfrogging Labour and the Conservatives. Membership of the party has now reached around 215,000, up from 65,000 when Polanski took over. There are big opportunities for the Greens to make breakthroughs in English local elections and parliamentary elections in Wales and Scotland on May 7. In London, and no doubt elsewhere, there is considerable energy and optimism in local parties. Members are confident in gaining footholds in councils as a springboard to winning parliamentary seats in 2029.

These green shoots may well augur a green spring (sorry for another metaphor), but strategic challenges remain for the Green Party. Activists will rightly be focused on carrying the message of hope and winning seats right now, but it is in the interests of everyone that wants a more equal, democratic and sustainable society to think hard about what the rise of Green Party implies in an era of multi-party politics where Reform is leading the polls.

That’s why I’m writing a report for Compass exploring the rise of the Green Party. It will be an optimistic but sober deep dive into the strategic challenges that will determine whether this really is a green tidal wave or a green bubble. I’ll be asking how the Green Party can move from a fringe party to one that wields real political power, including:

• How the party broadens its appeal without watering down the eco-populist vision that has enthused its large and growing membership.
• How the party empowers its membership whilst professionalising its campaigning, communications and policy making structures as it comes under greater scrutiny.
• How it will focus resources across target areas and whether it will be part of a new Popular Front against the far right.

The next general election will likely take place under First Past the Post across 650 seats. That is a very different challenge to a by-election and the stakes are incredibly high. In England alone, there will be Lib Dems, Greens and Labour candidates all positioning themselves as the ‘progressive’ option best placed to beat the Tories or Reform. Constituency-level polling in such a dynamic nationwide campaign will be a highly imperfect guide to progressive voters trying to tactically vote for the best placed candidate.

The French Nouveau Front Populaire managed to come together to defeat the far right in 2024 and this could be a model to emulate. However, it would require a level of cooperation we haven’t seen so far. Polanski has vowed to replace Labour, who are currently in government, whilst Labour’s French equivalent, Parti Socialiste, are not. Likewise, Labour’s attack lines on the Green Party, unflatteringly comparing the populism of Polanski with Nigel Farage, doesn’t exactly pave the way for joint working.

Local Green parties are already doing informal deals with other parties around the May elections, agreeing to concentrate their resources strategically. Extending these agreements nationally beyond local left activists, who most likely already know each other but are currently in different parties, is another challenge altogether. Similarly, the national Labour Party machine will be unlikely to cede seats without a fight; it isn’t in its DNA.

Over the next couple of months I’ll be interviewing key figures in and around the Green Party including pollsters, campaigners, policymakers and strategic communicators to explore these issues. I’ll be speaking to ex-Labour members that have made the switch over, seasoned Green Party activists and political professionals with an outside perspective.

The failure of Corbynism shows that a large party membership and populist left-wing policy platform isn’t enough to win real political power. The Green Party will need critical friends if they are to make the most of this opportunity. Already, scores of people have been in touch and offered to be interviewed for the project. Compass members that want to feed in their thoughts or would like to be interviewed for the project are warmly invited to email me.

Joseph Cox is a freelance researcher and writer. He spent his formative years at Compass and has since had a career working at the intersection of policy analysis, community building, campaigning and communications.