The loud knock on the family’s farmhouse door was at midnight as they got ready for bed. Outside, five Islamic State fighters, Kalashnikovs hung on their shoulders and faces hidden by black scarves, were searching for girls to kidnap.

‘We opened the door and they saw my wife’s teenage sisters Sabiha and Sajida. The fighters told us they were going to steal them because they were beautiful,’ says Kafi Osman, anger still burning in his eyes at the memory.

‘We cried and the girls wept as they were led outside and driven away in an open truck. We have heard nothing of them since.’

The girls’ kidnap in the northern Iraqi town of Makhmur came as jihadis from Islamic State (also known as IS and Isis) took control of it street by street. They beheaded men, raped women and then captured their trophies of war — virgins to be sex slaves or jihadi brides.

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One teacher told of her horrifying capture by the city’s ruthless all-women police unit, the Al-Khansa brigade (above), created to enforce IS rules. ‘They said my eyes were visible through my veil. I was tortured. They lashed me'

The Osman family now believe that Sabiha, 18, and Sajida, 16, are prostitutes in Raqqa, a seven-hour drive across the Iraqi border in Syria and the Islamic State’s self-proclaimed capital, awash with jihadi fighters.

It is a place of medieval barbarism, terror, torture, abuse and odious controls over the 100,000 women who live there. Some women are trapped in the city against their will.

They did not escape before IS marched in two years ago, building a Sharia court on the football pitch and imposing a regime where grisly public executions take place by stoning and crucifixion in the main square after mosque prayers on a Friday.

Others are radicalised jihadi brides from the West, including three pupils from Bethnal Green, East London, who were pictured last week walking in the town with a woman minder in a burka holding a Kalashnikov.

The third group of women are the unfortunates kidnapped in enemy territory by IS fighters, taken to Raqqa, and imprisoned in a life of sex slavery.

I remember one woman walking with her husband wearing a robe with images on it. We arrested her and took her to the Al-Khansa base. I lashed her with my own hands

Whatever the reason for living in this hellish place, all women are prohibited from going outside or travelling without a male relative. Islamic State imposes a strict dress code demanding all females from puberty upwards wear two gowns to hide their body shape, black gloves to cover their hands, and three veils so their faces cannot be seen, even in direct sunlight.

Women have been publicly buried alive in sand for breaking the code. One former Syrian schoolteacher trapped in the city told Channel 4 in a documentary, Escape From Isis, to be aired next week: ‘We have no freedom. We cannot go out on the balcony or look through the window. They will arrest a woman if she wears perfume or raises her voice. A woman’s voice cannot be heard.’

The teacher told of her horrifying capture by the city’s ruthless all-women police unit, the Al-Khansa brigade, created to enforce IS rules. ‘They said my eyes were visible through my veil. I was tortured. They lashed me. Now some of them punish women by biting. They give you the option between getting bitten or lashed.’

As many as 60 British women, including Aqsa Mahmood, the 20-year-old Glaswegian woman who left her family to become an Islamic State apparatchik last year, are thought to be members of the brigade. They are paid up to £100 a month, a fortune in the Islamic State bad-lands.

One former Al-Khansa enforcer, a young Syrian woman called Umm Abaid, told the filmmakers how she had led a normal life until the arrival of IS and the imposition of Sharia law in Raqqa, once a cosmopolitan city where the sexes mixed freely.

Another grim glimpse of life in Raqqa emerged last weekend from Amira Abase (left), who was 15 when she and fellow Bethnal Green GCSE pupils Shamima Begum (right), 16, and Kadiza Sultana (centre), 15, ran away from home in February. Two of the girls have since married jihadi fighters, although they refuse to say which of them is still single

As many as 60 British women, including Aqsa Mahmood (above), the 20-year-old Glaswegian woman who left her family to become an Islamic State apparatchik last year, are thought to be members of the brigade

‘I went to school, to coffee shops,’ she said, ‘but slowly, slowly my husband [a Saudi Arabian IS fighter killed in a suicide bomb attack] convinced me about Islamic State and its ideas. I joined the brigade and was responsible for enforcing the clothing regulations.

‘Anyone who broke the rules, we would lash. Then we would take her male guardian, her brother, father or husband, and lash him, too.

‘Even when I was off duty, if I was with my husband in the car and we saw a woman dressed wrong, he would stop and tell me to deal with her.

'I remember one woman walking with her husband wearing a robe with images on it. We arrested her and took her to the Al-Khansa base. I lashed her with my own hands.’

Umm fled to Turkey after IS tried to force her to remarry within weeks of her husband blowing himself up.

The terrifying brigade even stops buses to check women passengers. If one is found breaking the code, all the passengers are forced to get off and the bus is refused permission to proceed. The driver can be lashed because he let the woman on board.

Some of the Al-Khansa members operate undercover, posing as housewives, mingling in the crowds to listen for any dissent.

They also run brothels where kidnapped girls, like Sabiha and Sajida, are expected to satisfy fighters returning from battle. Those who have escaped, by a miracle, say they have slept with 100 different fighters in a few weeks.

Even girls who have gone willingly to Raqqa, thinking they were going to marry one fighter, have found they are expected to spend a week with their new ‘spouse’ before they are ‘divorced’ by an Islamic cleric and married to another fighter for a week.

And so the marriage merry-go-round goes on.

Yet, incredibly, still more Muslim girls and women from Europe, and notably the UK, are arriving in Raqqa to join IS. What can possibly induce them to run away to join its ranks?

A group of captured Yazidi and Christian women are chained together and marched to a sickening sex slave market where they are sold to become wives for Islamic State fighters

Emily Dyer, a research fellow with the Henry Jackson Society, a respected Westminster think-tank, spends hours each day tracking social media messages sent to the West by jihadi brides.

‘The fighters are seen as lions and wives as lionesses raising future jihadists,’ she says. ‘Joining up is seen as an adventure for girls who are bored with life here. You cannot overestimate the seductive attraction of IS to some of them. They see Muslims being attacked abroad and want to do something about it.

‘Even the violence and sexual abuse against women don’t seem to stop them leaving. In Britain, they are exposed to a barrage of brainwashing on social media coming from the Islamic State. It tells them that not supporting the “cause” is wrong. There is strong moral pressure on Muslim women to go and play their part in building an IS caliphate.’

How could we stay in a town run by the Islamic State when we have our little daughters to protect? We were frightened the fighters would want them too

Explaining the recruitment process, she says: ‘Their friends come online with a cool new identity and tell them it is paradise, with groceries supplied, medical help for free, a place to stay. They meet a fighter online, he proposes, and says come to Syria.

‘It sounds an attractive option when being a Muslim woman in the West may be a hard prospect.’ Emily suggests the possible difficulties: perhaps a forced marriage, a limited life outside the home, and a lack of freedom compared with their non-Muslim peers.

Once they arrive, their dreams can be shattered. Emily’s analysis of internet messages shows that many jihadi brides find Raqqa a shock. Under IS prohibitions, single women live in all-female safe houses called maqqars. If they are married, they must be only mothers or housewives unless selected to be IS ‘enforcers’ or fighters.

A girl tracked by Emily on Twitter said: ‘I’m fed up. They make me do the washing up.’ Another said: ‘I’ve done nothing except hand out clothes and food. I help clean weapons and transport dead bodies from the front. It’s beginning to get really hard.’ One complained: ‘My iPod doesn’t work any more. I have to come back [to the West].’

A fourth wrote: ‘They want to send me to the front but I don’t know how to fight.’

Another grim glimpse of life in Raqqa emerged last weekend from Amira Abase, who was 15 when she and fellow Bethnal Green GCSE pupils Shamima Begum, 16, and Kadiza Sultana, 15, ran away from home in February. Two of the girls have since married jihadi fighters, although they refuse to say which of them is still single.

Under IS prohibitions, single women live in all-female safe houses called maqqars. If they are married, they must be only mothers or housewives unless selected to be IS ‘enforcers’ or fighters. Above, IS fighters march through Raqqa, Syria

Amira, in messages on Twitter and Kik Messenger (an encrypted service) said that women in maqqars are forbidden access to mobile phones or the internet. They are then prepared for marriage to a jihadi, even if they are young teenagers. ‘The Prophet Mohammed’s favourite wife, Aisha, got married to him when she was nine,’ she said.

She advised British girls wanting to join IS not to tell their families, to bring as much money as possible, ‘lots of bras’, black khimars (long Islamic dresses) and black niqabs (full face veils) — ‘you can’t leave the house without a niqab.’

It was fear of IS’s treatment of women that led Kafi Osman, a 27-year-old Iraqi Kurd and Muslim, to flee with his 44-year-old wife Balqesa and children, Sara, four, and Elaf, three, the day after Sabiha and Sajida were taken.

After a month hidden in the back of a truck, which crossed into Turkey then drove through Eastern Europe and Germany, they arrived on the northern coast of France. They had paid £16,000 in cash, which Kafi had hidden at the family’s farmhouse, to an Iraqi agent.

‘How could we stay in a town run by the Islamic State when we have our little daughters to protect? We were frightened the fighters would want them too.

The Islamic State fighters say they are Muslims, but they have no religion but killing

The jihadis took over Makhmur in 20 minutes, killed the men, and then began knocking on doors looking for girls to steal.’

The Osmans are now among 3,000 refugees, asylum seekers and economic migrants massing on the French coast trying to hide on lorries and trains coming to Britain. The tragedy is that Kafi and his family genuinely deserve help.

When I met them, I gave them food and medicine for the girls, who had chills, while their father explained: ‘When we ran away from Makhmur, the four of us lay down flat on land outside the town hoping we would not be found by the Islam fighters. We were there for days without food and only a little water. At last I found someone who knew a man who would drive us to Europe.

‘The price was high, all my savings which I ran away with in my pocket. I reasoned that I could always get money again but nothing would bring back my little daughters if the Islamic State got them.

‘When we were on the journey, the driver hid his face so I could not report him to the police. We had to put our hands over the girls’ mouths to stop them talking at borders.’

At last, the driver told them they were in Britain. They got out and stood by the road as he drove off. Kafi says: ‘It was late evening and I looked at the street signs. He had cheated us, he had dropped us in France. I was so disappointed.’

In the darkness, the family walked for three hours and finally saw a sign for Dunkirk. In the town the next morning, they were told by another Iraqi migrant about a makeshift camp, hidden in trees in Grande Synthe, a small town three miles away. There the other migrants, who rarely see young children, offered them a hut to live in.

Today Kafi, who speaks good English and worked as an interpreter for an Italian oil company in Makhmur, while helping out on the family farm, says he will never return to Iraq.

As he pulls his coat around his shoulders on a chilly French day, he says: ‘The Islamic State fighters say they are Muslims, but they have no religion but killing. I did not want to bring my daughters up in a caliphate run by them.’ He comforts himself that he has saved his daughters from Sabiha and Sajida’s fate.

As we say goodbye, Balqesa begins to cry uncontrollably at the mention of her sisters’ names, while her two beautiful children reach up their hands to their mother’s face to try to stop her tears falling.