France’s Europe minister, Nathalie Loiseau, last week told a group of French citizens at the French ambassador’s residence in Kensington that Brexit had become the British equivalent of the Dreyfus affair – the 19th-century scandal that divided families, parties and regions.

On Thursday afternoon in Salzburg, Emmanuel Macron adopted the role of Emile Zola, accusing a conspiracy of liars of misleading the British people in the referendum, then running away and refusing to take responsibility.

His remarks infuriated leavers, including some in the Labour party such as Caroline Flint, who said imperious insults from the French president were not going to warm the British public to the cause of remain. What plays well to the Berlaymont gallery does less well in Burnley.

But that is to misunderstand the complexity of Macron’s motives. He is not just locked in a negotiation with the British to protect the single market, he is in a battle to defeat populism, of which Boris Johnson’s referendum campaign was a harbinger.

His horizon does not just stretch to 29 March 2019, the current date of Brexit, but to 23 May, the date of the next European parliament elections. His target is not just the stubborn illusions of the British negotiators – he took care to praise May’s courage in his remarks – but the simplicities of Steve Bannon, Viktor Orbán, Marine Le Pen and Matteo Salvini.

It is May’s misfortune that the two targets interconnect, making the task of a Brexit agreement favourable to Britain that much harder. Brexit cannot be ringfenced from what else is happening in Europe.

The Greek prime minister, Alexis Tsipras, said: “In this fight, all progressive, democratic and pro-European forces have a duty to stand side-by-side on the same side of history,. We should not let Europe slide back into the past.”

Guy Verhofstadt, the head of the Liberal group in the European parliament, who is courting an alliance with Macron’s En Marche, this month told the Ouest France newspaper: “Fortunately, we have Brexit. It illustrates the populist wave but it has also provoked a resurrection of attachment to the EU.”

The Hungarians are equally clear about the battle ahead and have put Macron in their crosshairs. Péter Szijjártó, the combative Hungarian minister of foreign affairs, said: “Hungary is attacked by pro-immigration forces led by Macron ... Their goal is to change the composition of people living in Europe. We resist that ... Whatever the pressure, the Hungarian government will fight for the cause of Europe and the homeland.”

It is hardly a surprise that the most vocal supporter of Brexit at Salzburg was Orbán, the Hungarian prime minister.

The populists may be riding primarily on an anti-migrant wave, but in this all-stakes battle, Britain cannot be seen to be rewarded.

If Macron could help engineer a further EU referendum in the UK he would welcome it, but above all, there can be no Brexit solution that provides comfort to governments that intend only to abide by the rules that suit their interests. A Europe that protects will be the dominant theme of the liberal progressive campaign for the May elections. Follow the populists and you end up in the chaos of Brexit.

For the British remainers, now in more coordinated diplomatic contact with European capitals, the risk is their campaign will become collateral damage in a wider war.

In their parallel diplomacy, remain has been urging European leaders to show their support for a vote on the final terms, primarily by saying they are open to extending the negotiating period if deadlock in the UK parliament provokes the genuine prospect of a British rethink. The call by Joseph Muscat, the Maltese prime minister and a confidante of Tony Blair, for a further referendum was on the right side of the line of interference.

Equally, remain supporters are pressing the commission not to offer the EU a blindfold Brexit in its political declaration – a short statement on future trading relations that leaves much to be negotiated after Brexit. Loiseau, in her remarks to Chatham House last week, stressed French objections to this solution.

The French are not playing the role of spoilers. They want a deal, but one that protects the integrity of the four freedoms of the single market. Anglo-French interests in the field of defence and security coincide too much for a breakdown. For instance, on the day Salzburg ended in acrimony, the French armed forces minister, Florence Parly, met her British counterpart, Gavin Williamson, to discuss the European Intervention Initiative, a plan for a flexible practical voluntary intervention force composed of nine European nations both inside and outside the EU.

The French initiative has been created in part with Brexit in mind, ensuring cooperation between the two nations with the greatest military culture in Europe.

In the weeks ahead, with so many forces already in play, there is a new element: the interplay between the interests of the pro-European leaders and supporters of remain.