Late last week, officers Lucenay and Roux of the municipal police were resuming their patrol of the beaches that extend from the vast marina complex at Villeneuve-Loubet along the Côte d’Azur towards Nice. This would normally be a routine duty during peak season, but now they have an extra task: to look out for “burkinis” – swimwear that covers the body and head, preferred by orthodox Muslim women but now banned by the town.

Mayor Lionnel Luca made his municipality the third to outlaw the garment as a “provocation” after riots in the Corsican resort of Sisco last weekend, when tourists taking photographs of women in burkinis were attacked by men of Maghreb origin. Cars were burned, seven people were badly injured and five men were arrested on charges of armed assault and face trial next month.

Cannes followed suit in banning burkinis, then Villeneuve-Loubet, then six more towns. Four women have been cautioned, liable to fines of €38 each. Cannes police said other women approached by officers had left the beach or changed into bikinis.

While Lucenay and Roux insist that they cannot speak officially, they do admit to an element of what they see as absurdity in adding the new category of “religious offences” to their usual roster of “promiscuity offences” and “public order offences”.

But the mood is hardening. In Nice – scene of the 14 July massacre when a 19-tonne truck was deliberately driven into crowds celebrating Bastille Day, killing 85 people – mayor Christian Estrosi has thrown down a gauntlet to the Socialist prime minister, Manuel Valls. “What measures,” asked Estrosi in relation to the burkini, “does the government intend to take to fight these phenomena which you yourself denounce?”

Estrosi – like his counterpart, David Lisnard, in Cannes – is a member of Nicholas Sarkozy’s Republican party, anxious to harden its position on the right for fear of losing ground to Marine Le Pen’s Front National in next year’s presidential elections. His demand raises the stakes in pursuit of a national ban – following those on veils in schools in 2004 and niqabs on the street in 2014. The difference is that while women wearing niqabs are in theory liable to a €150 fine, men obliging them to do so face fines of €30,000 and a year in jail; with burkinis, liability rests with the woman.

Valls came to Marseille last week to say that burkinis were “expressions of an archaic vision of women in public places … The burkini is not a new swimwear fashion; it’s the transmission of a political project, against society, founded notably upon the subjection of women. Some people try to portray those who wear them as victims, as though we were calling liberty into question. But there is no liberty to subjugate women.”

The premier added: “I understand mayors who, in this moment of tension, have reflexes in search of a solution, avoiding trouble with public order. I support those who have issued bans.”

The burkini row may seem banal, and to some a surreal inversion of laws in Islamic countries, but it has become yet another flame in the murderous tinderbox of Islamism in France, invoking issues of control over the body, religious freedom, racism, provocation, terrorism, Islam and Islamophobia, republicanism and what the French call laïcité. Laïcité is the hardest for people outside France to understand: our words “laity” and “secularism” fail to express the depth of allergy to all things theocratic, which is endemic to French societal fabric since the revolution.

Writing about the burkini ban, Le Figaro commented: “Foreign media, especially in Anglo-Saxon countries, just do not comprehend our French tradition of banning Islamic dress.”

The row over burkinis originated in 2014, when the municipality of Wissou, in Essone near Paris, banned them at an urban beach. The Collective Against Islamophobia in France (CCIF) challenged the ban in court, and won. When Wisson reinstated the ban, the CCIF successfully challenged it a second time.

Then came the Islamist onslaught against France, beginning with the Charlie Hebdo massacre in January 2015, up to the slitting of a priest’s throat in Normandy two days after the Nice atrocity. Most French people wonder how much more they can take – but brace themselves for more – while others argue that draconian measures in response encourage racism, isolate the Muslim community and radicalise it.

The ironies are replete: it was on the same now breast-baring beach at Cannes that Brigitte Bardot famously appeared in a bikini during the 1953 film festival – when the garment was banned (for showing too much skin) in Spain, Italy, Portugal, Belgium and towns along the French Atlantic coast.

Also on this beach, Amedy Coulibaly, the Isis-inspired killer of four people in a kosher supermarket last year, was pictured with his girlfriend, who wore an eye-catching two-piece swimsuit. Just along the coast, the Saudi King Salman has his palace and private beach access – there was little information to be had from there last week on the royal household’s balance of bikinis to burkinis, if any.

A “burkini-only” event was banned this year at a pool in the Bavarian town of Neutraubling. The issue was reignited in France after a swimming club called Sweet 13 advertised a women-and-children-only day at Speed Water aquapark near Marseille. Publicity for the event said that “burkini/jiheb de bain” should be worn. The Facebook page of Sweet 13 has now been taken down, but a screenshot shown to the Observer indicates interests beyond swimming – with inflammatory language about “infidels” and “unbelievers”.

The outcry was led by a Republican senator from Marseille, Valerie Boyet, who said it “raised issues of provocation and the rights of women”, and the event was banned. Boyet has since claimed burkinis are “part of an encroachment by Islamist extremism in this area, along with frequent wearing of niqabs on our streets, against the law”.

After the ban at Cannes, which also cited “hygiene”, the CCIF was joined by the League for Human Rights in a legal challenge through the administrative court in, of all places, Nice. This time – a measure of how things have shifted in France – the bans were upheld. Judge Dominique Lemaître ruled that burkini bans were “in accordance with the first articles of the constitution [that France is a République Laïque]” – which was mayor Lisnard’s defence.

Villeneuve-Loubet is a split-level community, between what is probably the ugliest marina sprawl along this coastline and its loveliest unspoiled hillside village – convivially mixed-race, with steep climbing streets. The first world war hero Maréchal Philippe Petain made his home here in 1920 before becoming head of state of the Vichy puppet state after the Nazi victory over France in 1940.

The local mayor since 2014, Luca is also a deputy for the Republicans, a member of the Popular Right tendency who criticised Sarkozy for being “soft” while president. His parliamentary record shows a tough line on dual nationality for immigrants and passionate support for Tibet, whose flag hangs alongside those of France and Europe outside his hôtel de ville, with its ochre walls and pastel shutters.

As in Cannes, the text of Luca’s ban makes a direct connection with “recent terrorist attacks” – specifying Nice and Normandy – and says the ban is imposed “in this context” and that of the extended state of emergency.

He adds: “I think we need to avoid proselytisation which poses a threat to public order. I don’t think this is religious dress; there is nothing in the Qur’an to say you have to wear a burkini. Those who use this as a pretext are canvassing an ideological provocation, which – given the attacks we have been through – is indefensible.”

For the League of Human Rights, the secretary of the Cannes-Grasse region, Hervé Lavasse, insists that: “Laïcité guarantees to every citizen a free conscience and freedom of religious expression. Do we want a fashion militia like countries of the mullahs?” He warns that the bans “are a perfect recruiter for radicalisation. How can we not fear that, with attitudes as exclusivist and repressive as these, many of our compatriots will feel excluded?” Already, internet messages threaten: “We men will defend our women in burkinis.”

On a bench near the beach at the working-class resort of St-Laurent-du-Var, midway between Villeneuve-Loubet and Nice, a woman called Ghada – in a robe, and veiled – shrugged when asked about the row, saying: “It’s crazy”. Her friend, wearing a burkini (still legal here), declined to discuss her preference and went for a swim.

Both camps are becoming entrenched. “I’d hardly seen a burqa and never seen a burkini until recently,” said Philippe Bessone, who owns a seaside apartment at Villeneuve-Loubet. “Now, both are proliferating, and I’d rather not see either.”

Resting on benches outside the CAP 3000 shopping centre, Walid Rezgul said: “What next? Cinemas and parks prohibited to Muslims? They want us to become invisible.”

But Saliha Thiriet, a Muslim Republican in Cannes, argues that “after the Nice atrocity, we need to comport ourselves carefully, not get carried away in anger. It could be that the burkini ban is a good thing for us.”

In the politically toxic warm sea breeze, it is a relief to find a mixed group slouching around tables outside McDonald’s in St Laurent-de-Var, drinking from a bottle of rosé obviously not purchased inside.

“Hygiene?!” balks Stéphane Blanchard, “what about all those people pissing in the sea, and motorboat fuel?”

“I can’t swim, and don’t much like the beach,” says Hiba Kahlaoui. “But if I did, I’d wear a bikini! I feel sorry for the women.”

“It’s all provocation,” adds her friend, Corinne, who is at teacher training college. “Provocation with all the Islamic dress we never saw here five years ago, and provocation by the racists. This country needs peace, not provocation.”

Ed Vulliamy