A pessimist might have concluded that the lights were going out in Europe, with the far right ascendant in France, Germany and beyond. On Sunday, Marine Le Pen’s National Rally was supposed to cement this narrative by winning the most seats in the second round of the French legislative elections. But it was not to be. The leftwing New Popular Front – an alliance whose largest cohort, La France Insoumise, is led by the unapologetically radical Jean-Luc Mélenchon – came top instead, surprising observers and delighting the country’s antifascist left. No countries are identical, but France could offer a portal into Britain’s future, with both grim challenges and potential opportunities. See it like this: it was as if a left alliance including the French equivalent of Jeremy Corbyn, ranging from the Green party to Ed Miliband-type Labourites, saw off Nigel Farage. Its programme: an unashamedly social democratic formula of taxing the rich, public investment, reversing attacks on pensions and raising public sector wages. And in this scenario, of course, Keir Starmer is the “centrist” President Emmanuel Macron. When Macron first secured the presidency in 2017, he was widely hailed as the antidote to “populism”, a term that has often been stretched to conflate anti-democratic, far-right extremism with the left. Back then, Marine Le Pen’s party had only eight seats in parliament – similar to today’s Reform showing. After five years of Macron, that tally surged to 89, and on Sunday night – despite defying polls predicting victory – the RN and its allies bagged 143 of the National Assembly’s 577 seats. This was no victory for the French president. After his party was routed in European elections earlier this year, Macron dissolved the legislature. His gamble was this: a fragmented left would not get its act together, so he could frame the contest as a straight fight between his profoundly unpopular presidency and the far right. Defying expectations, the left – bringing together Mélenchon’s France Unbowed, the rump of the old Socialist party, the Communists and Greens – forged an alliance within hours. It was they who prevented Macron handing the French nation to the far right on a platter. This was despite attacks not only from France’s far right but the centre. Bruno Le Maire, Macron’s finance minister, savaged Mélenchon’s party as a danger to the Republic alongside the far right. The left front was portrayed as a cesspit of antisemitism, even as it fought against a political movement that has racist politics as its core. Sound familiar? Indeed, France is where the “horseshoe theory” – which in effect equates the far right and far left – goes to die. Macron’s strategy for defeating the far-right menace has been to adopt their rhetoric and policies, with some dilution. After first winning the presidency, he clamped down on asylum seekers; more recently, he drove through an immigration bill that restricted migrants’ access to social security, made it harder to bring loved ones into the country and stopped giving automatic citizenship to children born on French soil to foreign parents. (Marine Le Pen claimed the bill as an “ideological victory”.) His government railed against every rightwing bogeyman from the “Islamist hydra” to “woke culture”. What lessons, then, for Britain? Macronism itself was the logical extension of the failed Socialist presidency of François Hollande, who came to power promising a break with rightwing austerity, then did the exact opposite (indeed, Macron served in his government). The big difference here is that Britain is in a much worse state than when Macron came to power. After already devastating cuts to public services and living standards, a £20bn-a-year hole in the country’s finances must be filled just to stand still in our current parlous state, but Labour has adopted Tory fiscal rules and opposes hiking taxes on the rich, threatening yet more austerity. There is every risk Starmer will react to the Farageist surge by adopting rhetoric and policies that will legitimise them further, while failing to reduce the widespread economic insecurity that drives an appetite for scapegoats. Reform came second in 98 constituencies across Britain – 89 of them held by Labour. The far-right surge really could knock its majority over. So here’s a couple of suggestions. The Greens are now second place behind Labour in dozens of seats, from London to Sheffield: with a big push, they could win next time. The surviving parliamentary contingent of the Labour left should form a “progressive caucus”, including the four newly elected Green MPs and leftwing independent parliamentarians such as Corbyn. They could push for radical policies like tax hikes on the well off, public ownership, a drastic expansion of workers’ rights, and climate policies that raise living standards. Leftwing Labourites should be bold. After all, the Labour leadership will be more frightened of purging them after the demonstrated success of Greens and independents. This could be the nucleus of a British-style New Popular Front. France isn’t out of the danger zone yet: the far right may yet triumph. But the lesson is that without left unity in the face of a failed centrist project, there would be no hope at all. Owen Jones is a Guardian columnist