Zack Polanski has won the election to lead the Green party in England and Wales, with an overwhelming mandate for the party to adopt his vision to become a mass membership “eco-populism” movement directly taking on Reform UK.

Polanski, who was the party’s deputy leader and is a Green member of the London assembly, defeated Adrian Ramsay and Ellie Chowns by 20,411 to 3,705 votes in a ballot of party members. Ramsay and Chowns, who were standing as a co-leadership team, are two of the Greens’ four MPs.

Polanski took nearly 85% of the votes on a turnout of just over 37%, notably higher than the 22% seen when the post was last contested in 2021.

Speaking to a cheering crowd in London, the new leader promised to take on Reform and Labour, saying the Greens’ moment had come.

“This is the Green party’s time. People in this country are exhausted. They are tired, they are sick of working long hours, and never feeling secure,” he said.

“We know this political space has been ripe for charlatans like Nigel Farage and Reform millionaires who are pretending to serve working-class communities but are actually backed by the same billionaires who are destroying our democracies, our communities and our planet. So it is an absolute moral responsibility in this moment for the Green party to step up with the bold politics.”

On Starmer, he said: “My message to Labour is very clear: we are not here to be disappointed by you. We are not here to be concerned by you. We are here to replace you.”

Saying he wanted the Greens to aim for more than 30 seats at the next election, Polanski said he would not prop up a new Starmer government, adding: “I cannot imagine any scenario in which I would want to work with Keir Starmer.”

While a Polanski win had been increasingly expected by party insiders, the result – with Ramsay and Chowns winning only 5% of the possible votes from an electorate of just over 64,500 – was particularly emphatic.

It heralds what could be a markedly new chapter for the party, abandoning its longstanding focus on building up councillor and MP numbers in favour of a more radical, media-focused approach.

While Polanski has said he will still concentrate on electoral gains, his hope is to accelerate Green advances by adopting a more visible and sometimes combative tone in media appearances, with the hope of mimicking Reform’s rapid advances under Nigel Farage.

Answering media questions after his victory speech, Polanski said the success of Farage in getting his message across to voters was “throwing down the gauntlet” to other parties: “It’s time to be really ambitious, and to be visionary … Let’s raise our communications game. Let’s raise the boldness of our messaging.”

Ramsay and Chowns previously said while they acknowledged Polanski’s communication skills – he is a former actor – they were concerned his more overtly leftwing approach could put off moderate voters, especially in the sort of rural seats they represent in parliament.

Asked whether he would cooperate with the new leftwing party being launched by Jeremy Corbyn and Zarah Sultana, Polanski said it was too early to talk about alliances, and also a matter for the wider party. It was better, he said, to think of “intellectual coalitions”.

He said he had talked to Corbyn about an inquiry into the situation in Gaza proposed by the former Labour leader: “We don’t need to be in the same party for me to support that. We don’t even need to be ‘allies’ for me to support that. What I see is a politician who is doing strong, principled work that aligns with the things I care about and the party cares about, and I think that’s different.”

Corbyn congratulated Polanski in a post on X, saying: “I look forward to working with you to create a fairer, kinder world.”

Ellie Reeves, the Labour chair, also congratulated him but said the new Green leader “must level with the British people” about whether he backed continued Nato membership, after he said during the campaign that Donald Trump’s approach made this unfeasible.

After a sometimes bruising campaign, Polanski paid tribute to all the party’s MPs, particularly Ramsay, who was first elected as a councillor two decades ago.

He ended his speech with an appeal for voters enthused by his message to sign up: “If you’re feeling hopeless, if you’re feeling in despair, if you’re feeling politically homeless, there is a political home for you.

“I promise you nothing will make you feel more inspired, more ready to get out there, and more like we can turn our country around than joining the Green party. So join the Green party today.”