Inside drab terraced housing, with a plentiful supply of tea and biscuits, a parallel British legal system is in operation.

This is the view of Machteld Zee, a Dutch researcher who gained unprecedented access to sharia courts in London and Birmingham that she believes conduct their work “in the shadow of the law”.

Ms Zee, who describes herself as “an atheist – like 70 per cent of the Dutch” – decided that the topic of her law PhD at Leiden University would be on how legal systems in different states interact with religion.

The 31-year-old from Gorinchem in the Netherlands was looking for a case study for her thesis, and heard about the sharia system in Britain.

An estimated 30 sharia councils exist today in the UK, giving Islamic divorce certificates and advice on other aspects of religious law. They have garnered fierce criticism, particularly for their treatment of women seeking religious divorces, who make up the core clientele.

Sharia law is the Islamic legal system, derived from the Koran and the rulings of Islamic scholars, known as fatwas. As well as providing a code for living – including prayers, fasting and donations to the poor – sharia also lays down punishments as extreme as cutting off a hand or death by stoning for adultery.

Critics of sharia law – such as Ms Zee, after conducting her research – say it downgrades women and is incompatible with European human rights legislation. Men need only say the word to have a religious divorce (uttering “I divorce you” three times), but women need the sanction of clerics. Without it, they risk being called adulterers if they do remarry.

In 2013, the Dutch academic began writing to all of the sharia councils in Britain she could find contact details for.

“I sent emails but heard nothing back. Then a professor at King’s College London, who has a different view of the councils, gave me some contacts,” she tells The Independent. To her surprise, she was extended two invitations after offering assurances that she wasn’t a journalist.

For two days in early July that year, Ms Zee presented herself at the unremarkable terraced building in Leyton, east London, that houses the Islamic Sharia Council. Some women were veiled; others wore lipstick. But what almost all these visitors to the council had in common was that they were there to ask for a religious divorce from their husbands.

She sat in a room with desk, chairs and tea and a supply of biscuits – for the judges (known as qadis) at least.

Sharia in the UK One case Zee witnessed, at the Islamic Sharia Council in London, involved a married couple with children, who asked if the woman’s first civil divorce was recognised religiously. It included the following exchange: Qadi: “You as a Muslim female, you should have known that you need a Muslim judge or an Islamic court or council for a divorce. Who told you that it was enough?” Wife: “My friends and family. The UK divorce does not count as anything?” Qadi: “It is going to be a difficult case. We are going to ask our scholars to give you the answers... Marriage is an act of worship”. Husband: “But I thought Muslims in a non-Muslim country need to abide by the laws of the land of the country they live in?” Qadi: “A secular judge does not do religious divorces. We have Islam. Secular courts do not have Islamic laws. Can a kaffir [non-Muslim] come in and judge Islamic matters?”

“The judges were very friendly,” she says. “We chatted between cases. The problem is not that they were mean but the foundation of their judice acts in a system of sharia Islamic law, in which the principle focus is making women dependent on their husbands and clerics.

“One judge said: ‘Under Islam, we should reconcile marriages even if there is violence’. They don’t care. It was shocking: they would have you cling to a marriage.

“There are also unfair custody statements. The woman has no idea this is a religious institution and she should go to a secular court [for her children’s interests] – and once she finds out, a British judge won’t switch parents after a few months.

“But in 2001, the European Court of Human Rights ruled that sharia law is incompatible with liberal democracy.”

Her book Choosing Sharia? is based on the 15 hours of cases that she saw at the council in London and another at Birmingham Central Mosque Sharia Council, alongside her extensive research into sharia law and other reports on sharia councils. She also investigated the Jewish Beth Din religious court, where she interviewed two judges.

Ms Zee’s analysis is blistering: these courts all treat women as less than equal and are incompatible with human rights law.

“I don’t say that you should ban sharia courts,” she says. “The ‘market’ for these councils, of women asking for a religious divorce, can be diverted to civil and criminal courts, where you can press charges, as happens in Holland.”

In her book, she describes in detail seven cases that she witnessed at the London council, each in front of one Islamic judge. In between cases, she says a qadi tells her they have 600 to 800 cases a year involving “divorce-seeking women who are on the receiving end of violence or maltreatment”. She goes on: “He tells me: ‘As long as marriage is sacred, reconciliation is our job’. Although, he tells me, reconciliation is mostly not successful, but sometimes it is.” Ms Zee describes cases including a female qadi-in-training seeing a young woman who has been visiting the Islamic Sharia Council for two years desperately seeking a religious divorce.

The woman has brought a solicitor with her. She says she was dissuaded from a civil marriage by her mother-in-law, and her husband refuses to co-operate until she has paid back her dowry of £10,000 worth of gold. But the woman claims she cannot return the dowry as her mother-in-law took it away again immediately after the wedding. She also claims that her husband took out a loan on her name the day they got married, further complicating her financial position.

The judge asks if she is sexually active, saying the husband has alleged that she is committing adultery. The woman denies this, and asks why – prior to a previous hearing – she was told on the phone that she was not allowed to bring anyone with her: no solicitor, friend, or family.

“She says that consequently, there was a hearing consisting of two male qadis interrogating her alone for quite some time about her sexual activities, in detail,” writes Ms Zee. “She had found that very uncomfortable and unprofessional. [The qadi] says it should not have happened and that she will look into it.”

After some more questions, the woman is told she need not come again to court and will hear “soon” whether her request for a divorce will be granted. “She looks as if she is ready to burst out in tears,” Ms Zee writes.

A separate case, in front of a young qadi in a white robe, is deemed another matter for “further investigation” after a couple present themselves to say that the wife’s first marriage had a civil but not a religious divorce (see panel).

Later, a woman married to a 50-year-old man asked if the qadi could intervene to stop her husband’s verbal and physical abuse. Ms Zee recounts: “She says: ‘He oppressed me to the maximum, he is violent, [and] physically treats me like a dog’. She wears a headscarf on his request. With ‘every little thing’ he threatens to divorce her. He is abusive both verbally and physically. She says he might have 10 wives for all she knows. He is currently in Tunisia. [The qadi] laughs a bit: ‘Why did you marry such a person?’”

In another case, a husband and wife and the qadi switch into another language to discuss their relations at one point. Ms Zee recounts: “After a short while, they switch back to English. [The judge] tells the man that he needs to swear on the Koran not to mistreat her any more. This case has been going on for four years. The man agrees to meet the conditions. The marriage is saved.”

But Ms Zee did witness some cases in London where the wife was successful in her appeal for a divorce. One woman – who was on one of multiple visits – said she had not seen her husband in four years after he moved abroad and refused to proceed with divorce, saying he wanted back his gold dowry. “She tells [the judge] she left the gold in his house when she left him. He is not stable, he is big-headed, arrogant and drinks alcohol. The reason he does not want to pronounce the talaq [assert his right to divorce her] is for revenge, she says. Now she has to pay him again, she does not have the money and she has a job, so she does not have any time for these procedures.”

Dutch researcher Machteld Zee, who gained access to the courts

The qadi announced the divorce, saying she did not have to return the dowry.

But when another woman asked for a religious divorce (in addition to ongoing civil proceedings) of a husband she had not seen in four years, and to whom she had given back an £8,000 dowry, plus an extra £30,000, Ms Zee writes that the qadi responded: “Debt is not a cause for divorce. You should help him. Why don’t you pay him more?” The academic writes that the judge then tried to persuade her to accept a polygamous marriage rather than pursue a religious divorce.

Last night Khola Hasan, a scholar at the Islamic Sharia Council who has worked there for six years, rejected Ms Zee’s allegations: “We are there for a reason, and people come to us,” she said. “We show them sympathy, we certainly don’t condone domestic violence or force women to go back: we are there to get women out of religious marriages.”

She described the allegations of bias towards men as “absolute rubbish”, saying: “The disputes are between a man and a woman and they are given equal weight. For anyone to claim men have more weight is a lie.” She said the council may consider legal action.

The council does have a prominent banner on its website saying “Stop Domestic Violence” and leading to a webpage which says: “In an emergency always call 999.”

Ms Zee’s experience in the Birmingham council was far more positive. There were three judges per case, plus an administrator on hand to write out divorce certificates. The four cases she writes about in her book all ended in success for the women, who recounted tales of husbands who physically abused them or got them into debt, and issued religious divorces.

She spoke to the qadis in Birmingham about her experiences in London. “I told them about the Islamic Sharia Council case where the qadi told a couple that kaffirs cannot rule on Islamic matters and that the woman’s civil divorce means nothing under Islam. They seemed to be appalled. ‘We totally disagree. We cannot have two laws. This is totally wrong. We live as British citizens and accept the law of the land.’”

The Birmingham Central Mosque did not respond to emails and phone calls.

Ms Zee is still critical of the entire sharia system, which comes under fierce attack in her 193-page book. She believes that the cases – by allowing men to delay proceedings – can end up locking women in “marital captivity”. She also claims that the councils are doing nothing to report domestic violence.

Zee will launch her book at an event organised by libertarian think-tank, the Henry Jackson Society, in the Houses of Parliament on 12 January. She is calling on the British government to introduce new laws to help women access the criminal and civil courts for religious divorce, as in the Netherlands, where in 2010 Dutch-Pakistani woman Shirin Musa won a precedent-setting civil case.

There, a judge imposed damages upon Ms Musa’s husband for each day of non-compliance with the court’s ruling that he had to release her from the religious marriage. He instantly did, and in 2013 “marital captivity” became a criminal offence.

Some campaigners feel even more strongly than Ms Zee. On Thursday 10 December, the International Day of Human Rights, groups including One Law For All will deliver a petition of more than 200 signatories to 10 Downing Street calling for the government “to dismantle parallel legal systems.”

They say that with cuts to legal aid and funding for women’s groups, vulnerable women – who might be taking their first steps away from an abusive relationship – are even more likely to go to sharia councils where those like Iranian Kurdish Women’s Rights Organisation’s Diana Nammi believe: “The whole system is stacked against women”.

Supporters of multiculturalism are reluctant to criticise sharia law, says Ms Zee. But should this legal system operating “in the shadow of the law” be banned? “No,” she reflects.