Hind Ahmas walks into a brasserie in the north Paris suburb of Aulnay-sous-Bois. Jaws drop, shoulders tighten and a look of disgust ripples across the faces of haggard men sipping coffee at the bar.

"Hang on, what's all this? Isn't that banned?" splutters the outraged waiter behind the bar, waving a wine bottle at her niqab. Ahmas stands firm, clutches her handbag with black-gloved hands and says: "Call the police then." But she decides there's no point fighting. We cross the road to a cafe where she's a regular. No one bats an eyelid; the boss certainly doesn't want to lose her custom. Ahmas is breaking the law by ordering an espresso and sitting in a booth in the window. But these days she is breaking the law by stepping outside her own front door.

In April, France introduced a law against covering your face in public. Muslim women in full-face veils, or niqab, are now banned from any public activity including walking down the street, taking a bus, going to the shops or collecting their children from school. French politicians in favour of the ban said they were acting to protect the "gender equality" and "dignity" of women. But five months after the law was introduced, the result is a mixture of confusion and apathy. Muslim groups report a worrying increase in discrimination and verbal and physical violence against women in veils. There have been instances of people in the street taking the law into their hands and trying to rip off full-face veils, of bus drivers refusing to carry women in niqab or of shop-owners trying to bar entry. A few women have taken to wearing bird-flu-style medical masks to keep their face covered; some describe a climate of divisiveness, mistrust and fear. One politician who backed the law said that women still going out in niqab were simply being "provocative".

Ahmas, 32, French, a divorced single mother of a three-year-old daughter, puts her handbag on the table and takes out a pepper spray and attack alarm. She doesn't live on the high-rise estates but on a quiet street of semi-detached houses. The last time she was attacked in the street a man and woman punched her in front of her daughter, called her a whore and told her to go back to Afghanistan. "My quality of life has seriously deteriorated since the ban. In my head, I have to prepare for war every time I step outside, prepare to come up against people who want to put a bullet in my head. The politicians claimed they were liberating us; what they've done is to exclude us from the social sphere. Before this law, I never asked myself whether I'd be able to make it to a cafe or collect documents from a town hall. One politician in favour of the ban said niqabs were 'walking prisons'. Well, that's exactly where we've been stuck by this law."

But despite all the fanfare surrounding the niqab ban, no woman has yet been punished under the law for wearing one. The first real test will come on Thursday, when a local judge in Meaux, east of Paris, will decide whether to hand out to Ahmas and a friend the first ever fine. They were stopped outside Meaux town hall on 5 May wearing niqabs and carrying an almond cake to celebrate the birthday of the local mayor Jean-François Copé, who is also head of Nicolas Sarkozy's rightwing UMP party and an architect of the ban. The cake was a joke, a play on the French word for fine, amende. They wanted to highlight the absurdity of a law that they say has increased a mood of anti-Muslim discrimination and driven a wedge through French society, yet seems not to have been taken seriously by the justice system. Sarkozy was accused of stigmatising women in niqab to win votes from the extreme right, yet the law didn't actually boost his poll ratings. Now, human rights lawyers are suggesting it could soon be overturned.

Only the French police can confront a woman in niqab. They can't remove her veil but must refer the case to a local judge, who can hand out a ¤150 (£130) fine, a citizenship course, or both. Some police have wrongly given on-the-spot fines, which were later annulled. Others appear to ignore women in niqab walking down the street, perhaps because they feel they have more important crimes to be stopping. The interior ministry says that since the law came into force in April there have been 91 incidents of women in niqab being stopped by police outside Paris and nine incidents in the Paris region. Each time, police file a report, but so far no judge has handed out a fine or citizenship course. The French justice ministry says "fewer than 10" cases are currently going through the courts and the lack of fines shows the state favours "dialogue" not punishment. But Gilles Devers, a lawyer acting for Ahmas and several other women in niqab, argued punishments were not being handed out because the niqab law contravenes European human rights legislation on personal liberties and freedom of religion. As soon as a fine is imposed, there will be an appeal right up to the European court of human rights in Strasbourg, which could rule against the law and expose the French state as a laughing stock.

If the French law is challenged in this way, the result would be crucial for Muslims across the continent. Belgium introduced its own niqab ban this summer, punishable not just by a fine but seven days in prison. In Italy, the far-right Northern League has resuscitated a 1975 law against face coverings to fine women in certain areas of the north. Silvio Berlusconi's party is now preparing an anti-niqab law. Denmark is preparing legislation to limit the wearing of niqabs; politicians in Austria, the Netherlands and Switzerland are pushing for outright bans. Thomas Hammarberg, the Council of Europe's commissioner for human rights, blogged this summer: "The way the dress of a small number of women has been portrayed as a key problem requiring urgent discussion and legislation is a sad capitulation to the prejudices of the xenophobes."

Ahmas grew up in and around Paris, where her father, born in Morocco, worked as a town-hall gardener. Her parents were not strict Muslims. She put on the niqab six years ago as an educated single woman who once wore mini-skirts and liked partying, but then rediscovered her faith. She says her now ex-husband had nothing to do with her choice. (The new law punishes men who force women to wear the niqab with a ¤30,000 fine, but none has yet been imposed.) Like many women in niqab who refuse to stay indoors, she is desperate for work. For years, she worked in call centres as a specialist in telephone polling. Even before the ban, she knew it would be easier to get work without the niqab, so at the office she would always pull back her veil, leaving her face exposed for the day. "Life is hard and I have to work. If my daughter wants something – even a Barbie doll – and I can't pay for it, it breaks my heart."

In January, at the height of the public debate on the niqab, Ahmas lost her job after her contract wasn't renewed. "I've contacted scores of employers looking for work. I always ask them if they accept the veil. They say, 'It depends what type. If it's tunic and trousers and a headscarf, that's OK, but a long robe is not.'" This is clear discrimination: "Totally illegal," she sighs.

Secular France has a complicated relationship with the veil. In 2004, all religious symbols including the headscarf were banned in schools. Even among Sarkozy's opponents there are very few feminists or socialist politicians who would defend the right to wear niqab in a country where secularism is one of the few issues that still unites a fragmented left. Barely a handful of people came to Notre Dame cathedral to protest against the law in April.

On the Cote d'Azur, Stéphanie, 31, still likes to go swimming in the sea off Nice wearing her niqab. But the former law student and convert to Islam tries to go when the beaches are quiet. The last time she went for a dip with her mother and 10-year-old daughter on a Sunday afternoon, a sunbather called the police. A group of officers arrived and hurried across the sand saying: "But Madame, what are you doing?" "I said: 'I'm drying myself.' They wrote in their notebooks, 'Swimming in niqab.'" Stephanie, who prefers not to give her surname, was summoned by the local state prosecutor. She arrived at court and agreed to lift her veil so security guards could check her identity, but they refused to allow her access until an exasperated prosecutor buzzed her in himself. The prosecutor, whom she described as "very human", wanted to better understand why she wore the niqab. She converted at 17 and put on the niqab several years later, long before meeting her husband. Her North African parents-in-law didn't like her wearing full-veil, and the marriage ended. Her own parents converted to Islam a few years later but don't believe a niqab is necessary. She told the prosecutor it was her choice and refused to stop wearing niqab. The prosecutor reminded her of the law and let her go with no sanction or punishment. He told the local paper, Nice Matin, that a woman in a veil was less dangerous than someone who had "double or triple parked".

Before the law, Stephanie would often be called names like "Batman, Zorro, or Ninja" in the street – often by pensioners. Now people favour swear words or sexual insults. She wants to work with children, but despite having a degree in theology, she can't find a job.

The first time Stephanie was stopped by police was for standing on a central Nice shopping street in May. A police officer illegally gave her an on-the-spot fine, which was later overturned. This summer, a bus driver refused to let her onto a bus with her daughter. "If I have a meeting, I'll always leave the house at 6.30am instead of 8.30am in case a bus won't take me and I have to wait 45 minutes for another one." Recently, after she had bought a cinema ticket for the latest Harry Potter film with her daughter, staff tried to stop her entering the screening. Eventually the cinema decided not to call the police because they didn't want to feature in the local paper.

The headquarters of the French Collective against Islamophobia is in a small ground-floor office on a cobbled street near Paris's Gare de L'Est. It doesn't promote the wearing of niqab but gives legal advice. "It's not the police I'm afraid of, it's the personal attacks on women by people acting on their own initiative in the street," says Samy Debah, the association's head.

The group's legal adviser says there has been "an explosion" in the number of physical attacks on women wearing the niqab. Many women say that their attackers were middle-aged or old people. In one recent case a young French convert was assaulted at a zoo outside Paris while carrying her 13-month-old baby. "Her child was traumatised by the zoo attack and is now being seen by a psychologist. These women blame themselves; they see a baby in that situation and think, 'It's my fault.'"

French businessman Rachid Nekkaz, who paid the fines of two women prosecu­ted for wearing the niqab in Brussels last year Photograph: Julien Warnand/AFP



At a cafe on the left bank, Rachid Nekkaz, a French property developer, explains why his association, Don't Touch my Constitution, was the only group to stage high-profile protests when the law came into force – he backed Ahmas's birthday-cake stunt and has set up a ¤1m fund to pay any fines over the niqab. His next, and most radical, protest action will be this Thursday, when his association announces its plans to field a woman in niqab for president in 2012. Nekkaz is personally opposed to the niqab and thinks it is fair to ban it in French state buildings. But he thinks outlawing it in all public places is "a gross attack on personal freedoms and the French constitution". "The perverse effect of this law is that women in niqab are effectively under house arrest," he says. He plays a voicemail message left on his mobile by the mother of French convert, thanking him for taking a stand and saying there are several converts in niqab in Grenoble now too afraid to leave the house.

There are no reliable statistics on who wears the niqab in France and whether they have kept wearing it since the law. It is estimated that only a few hundred women wear it, mostly French citizens. Muslim associations say a minority of women have taken off the niqab or moved abroad. Nekkaz says that more than 290 women still wearing niqab have contacted him: he says a large number were divorced with children, most were aged between 25 and 35, many were French of north African parentage, and many were living on income support. An Open Society Foundation report on women in niqabs in France in April found that of a sample of 32 women in niqab, none had been forced to wear the full veil. Many said they would refuse to take if off after the law came in, adding that they would avoid leaving home, or move abroad.

‘I’m insulted three to four times a day’ … Kenza Dride Photograph: Anne-Christine Poujoulat/AFP

Kenza Drider, a 32-year-old mother of three, was famously bold enough to appear on French television to oppose the law before it came into force. She refuses to take off her niqab – "My husband doesn't dictate what I do, much less the government" – but she says she now lives in fear of attack. "I still go out in my car, on foot, to the shops, to collect my kids. I'm insulted about three to four times a day," she says. Most say, "Go home"; some say, "We'll kill you." One said: "We'll do to you what we did to the Jews." In the worst attack, before the law came in, a man tried to run her down in his car.

"I feel that I now know what Jewish women went through before the Nazi roundups in France. When they went out in the street they were identified, singled out, they were vilified. Now that's happening to us."