It has been a good month for the Greens. In the local elections of 2 May, they enjoyed the biggest proportional gains of any party, more than doubling their council seats to 362. Still more encouraging for the Greens is that while the elections involved a certain amount of Brexit-fuelled protest voting against the main parties, huge surges in membership indicate that their gains were driven not by disaffection but by the growing importance of the environment as an electoral issue.

“We had 1,500 new members just over the weekend,” reveals Caroline Lucas, the Greens’ only MP. “There was a new member joining us every three minutes.” For Lucas, the most exciting wins in the local elections were in the 53 new wards – “places like Darlington, Derbyshire Dales, Carlisle, Colchester, places you wouldn’t necessarily associate with a strong Green presence” – in which Green councillors had never been elected before. Establishing a “foothold” on new councils is, for Lucas, crucial to the party’s success as it allows them to get past the “credibility barrier” that all smaller parties face. “Our experience is that once you get the first Green elected, the next time around you get more.”

That the Green wave is driven by voters’ desire for action on climate change rather than anger with the main parties is also confirmed by the fact that the Greens picked up seats in strongly pro-Leave areas, as well as the Remain heartlands. “I don’t think anybody voted for the Green Party without knowing what our position was on Brexit,” says Lucas, who was one of the founders of the People’s Vote campaign, but this did not prevent voters in Leave areas responding to “our position on a strong response to climate change and the crisis in nature that we face right now”.

The experience of Green candidates seems to have been unusually positive, too, on the campaign trail. While both Conservative and Labour candidates reported being verbally abused, threatened and in two cases physically attacked, Lucas says she has heard only “very positive reactions on the doorstep, and also an appreciation of the fact that we’ve kept our campaigning positive as well, rather than slagging off the other parties. We’ve been out there talking about our record, what we’re committed to, what Green councillors have already done.”

For Lucas, demonstrable results are vital to making people see the Green vote as more than an act of protest. It is the hard work of Green councillors, she says, that has allowed the party to make unexpected gains. In the predominantly white, working-class area of Chelmsley Wood in Solihull, for example, where average life expectancy is ten years shorter than wealthier wards a few miles away and where the BNP won a seat in 2006, persistent local effort by the Greens on issues such as public spaces and housing led this month to an 84 per cent share of the vote, as “people saw that we were a presence not just at election time, but year-round.” While the Chelmsley Wood result comes from a very low turnout (21.5 per cent), Lucas says it is an example of Green councillors “going into areas that have been, frankly, neglected by Labour for years”.

While Lucas is clearly very proud of the work Green councillors are doing, she is also realistic about the factors that create Green votes. “When environmental issues are in the news,” she acknowledges, “our vote goes up.” She credits “the David Attenborough film, Extinction Rebellion, the extraordinary youth climate strikes [and] the visit of Greta Thunberg” as elements that “touched a nerve in the population, who know that the way we’re living now just isn’t sustainable. And yet when you look at the other parties, they’re simply not stepping up to the plate.”

Lucas does not see much risk of Labour poaching the new Green vote by strengthening its own environmental policies because, she says, its environmental policies are not fit for purpose. Jeremy Corbyn’s call for MPs to recognise a climate emergency came, she says, “weeks, if not months, after I’d originally put down an early day motion in this place to call for exactly that.” Lucas points out that in March, Corybn’s colleagues in Holyrood joined the Scottish Conservatives and the SNP in voting down a motion by the Scottish Greens to recognise a climate emergency. She has asked Corbyn in the Commons if he would rule out subsidies for fossil fuels – “he avoided the question” – and notes that while “he personally doesn’t support the expansion of Heathrow airport, he refused to whip his MPs in that direction, and so under Labour you would still have the expansion of airports – aviation being the fastest-growing source of greenhouse emissions. They [the Labour and Lib Dem-led Cumbria County Council] have just given the green light to the first new coal mine in 30 years. This is not the action of a party that is taking the climate emergency seriously.”

She has put the question of airport expansion to Michael Gove, too – “he refused to answer” – and says that one of factors that is most likely to drive voters from the Conservatives to the Greens is a basic and obvious failure “to tell the truth, and to stop pretending that our record is much better than it is”. Voters are increasingly aware that government pronouncements, such as the oft-quoted idea that the UK’s emissions have reduced by 40 per cent since 1992, are hot air, because they do not count the emissions from aviation and shipping or the emissions embodied in products manufactured overseas. “The population,” Lucas says, “knows that the way we’re living now isn’t sustainable,” but most politicians have ignored the fact that this is changing the way they vote. “I don’t think they get it at all.”

Do the Greens, as a small party, enjoy the luxury of not having to come up with the pragmatic policy on jobs, trade and transport that answers the needs of the wider voting public? Lucas disagrees: without effective climate change policy it may be that within a generation or two, other policy will have ceased to matter. “If we’re serious that this is a climate emergency; if we believe David Attenborough when he says that if we carry on with business as usual, we could be facing the end of civilisation as we know it; if we look at the report from the intergovernmental panel on biodiversity that we are at risk of losing a million species... a million species. These are easy words to say but when you think about what they actually mean, it is horrific. A government that fails to do what is necessary is letting down not just this generation but future generations as well, in the most unforgivable fashion.”

But it is also the voters of the future that give Lucas hope. Young voters, she says, are behind “a green wave across much of the European Union, in places like Germany and the Netherlands – and it feels like that is happening now, here in the UK.”