Regional and presidential polls over the next two years will show whether the “green wave” that surged through a swath of big French cities earlier this summer heralded a fundamental redrawing of the country’s politics – or a transitory ripple.

In June’s municipal elections, Europe Écologie-Les Verts (EELV) – alone or at the head of leftwing majorities – held Grenoble, seized Annecy, Besançon, Bordeaux, Lyon, Poitiers and Strasbourg, and were part of winning coalitions in Paris and Marseille.

Amid a broad but not yet decisive advance by green parties across much of Europe, Yannick Jadot, an MEP and one of the French party’s most senior figures, hailed a “historic turning point”.

The results revealed “a desire for concrete ecology in action: solutions for commuting, housing, food, rebuilding local economies”, he said; France’s political landscape was being “remodelled around the theme of ecology”.

EELV aims to field a full list of candidates in regional elections due next year. Ecology was “no longer a political add-on,” another MEP, David Cormand, said at the party’s summer conference last week. “We are moving from a force of opposition, to a force of government.”

The party’s unexpected June election triumph built on an encouraging 13.5% – and third-place finish – in last year’s European parliamentary elections, and represented a remarkable rebound from a disastrous few years for France’s Greens.

Jadot withdrew from the 2017 presidential poll to boost the chances of the Socialist party candidate, Benoît Hamon – who then crashed out in the first round with 6.4% of the vote. In the ensuing parliamentary poll, EELV failed to win a seat.

But the party now feels that its local victories in former bastions of both left and right show that the foundations of French politics are shifting. The winning formula, it believes, lies in a broad political offering in coalition with a range of other leftist parties around the themes of ecology, social solidarity and a more representative democracy.

Critically, the party notes, France’s once dominant Socialist party was willing to play second fiddle to EELV in several successful municipal coalitions. “The time when we were behind the rest is over,” said Sandra Regol, the party’s deputy leader. “It’s now up to the rest to decide whether to join us.”

Some analysts think EELV may be right. Since the pro-business centrist Emmanuel Macron blew up France’s political landscape in 2017, crushing the main centre-left and centre-right parties on his way to the Élysée, most have assumed that the 2022 presidential race would be a repeat of his face-off with the far-right Marine Le Pen.

“But that’s not necessarily a given,” said Brice Teinturier of the polling firm Ipsos. “An offer that successfully unites the left and the Greens could have a real chance of making it to the second round.”

The pollster said the party was attracting, in particular, disappointed left-leaning Macron voters, and that its success reflected French voters’ continuing search for new forms of political expression beyond the left-right divide. “In 2017, that benefited Macron,” he said. “This time it was the Greens who looked different.”

There are reasons, however, to be cautious about EELV’s prospects on the national stage. Voters behave differently in local and European elections – where different concerns are in play – than in parliamentary and presidential polls.

EELV fared well in France’s cities, but may struggle to impose itself nationally. Crucial to its chances will be a credible presidential candidate – but the party is already bitterly divided over who it should select, and an Ifop-Fiducial poll published after the local elections had Jadot scoring just 8% in the 2022 first round.

June’s elections were also held in unusual circumstances, analysts note, with the second round delayed for months due to the coronavirus crisis. “The virus raised public awareness of the issues that EELV campaigns on,” said Ifop’s Jérôme Fourquet.

“Many viewed the epidemic through the prism of the environment, of excessive consumption, the destruction of our ecosystems. Voters were much more awake to a more localised, ecological approach. That played a part.”

Macron, furthermore, is not giving EELV a free ride: the president recently accepted all but three of the 149 recommendations of a citizens’ commission for the climate and has made green investment central to France’s mammoth €100bn (£90bn) post-Covid recovery plan.

His entourage, however, is divided on the best strategy for defeating EELV. Many more left-leaning members of Macron’s La République en Marche (LaRem) believe the only way is to out-green the Greens.

“We have to go bigger and faster on the environment,” one LaRem MP said. “That’s what voters expect. We will be punished if we don’t.”

Others believe that the presidential party must invent a “pro-business environmentalism”, with green technologies driving an economic revolution. Still others, mainly on the right, believe LaRem must counter EELV directly by attacking its credibility.

The Greens’ willingness to ally themselves with the French Communist party and far-left La France Insoumise – as well as the views of some of their newly elected officials – make them a soft target, many in the government believe.

The freshly sworn-in EELV mayor of Colombes, Patrick Chaimovitch, was recently forced to apologise after comparing the modern-day French police to the Vichy regime of the second world war.

EELV councillors have claimed that 5G technology is harmful to health, which is not supported by science; the EELV mayor of Marseille was confronted with a 2018 tweet in which she called for an end to compulsory vaccinations; and two EELV Paris councillors were excluded from the majority coalition after a heated row with the Socialist mayor, Anne Hidalgo.

The party’s supporters say such incidents are inevitable when activists become politicians, and will not deter voters persuaded by EELV’s core message. EELV’s opponents will argue that they preclude the party from becoming a serious political force.