Shamima Begum, the Bethnal Green schoolgirl, served in the Islamic State’s “morality police” and also tried to recruit other young women to join the jihadist group, well-placed sources have told The Telegraph.

She was allowed to carry a Kalashnikov rifle and earned a reputation as a strict “enforcer” of Isil’s laws, such as dress codes for women, sources claimed.

The claims are at odds with Miss Begum’s own account of her four years with the group, which she joined at the age of just 15.

Miss Begum, now aged 19, has insisted she was never involved in Isil’s brutality but spent her time in Syria as a devoted housewife to a jihadist fighter.

Miss Begum, whose discovery in a refugee camp in northern Syria in February sparked a public outcry, said she concentrated on bringing up the couple's children. They subsequently died of malnutrition.

Her husband, Dutch fighter Yago Riedijk, offered a similar story, saying Miss Begum “sat in the house” and that she would pose no danger to the British public if allowed back to the UK.

Miss Begum travelled to Syria in 2015 after making plans with three other girls from London credit: Laura Lean/PA

But The Telegraph has been able to piece together a different account of Miss Begum’s life inside the world’s most brutal terrorist organisation, and one which could complicate any possible return to the UK.

She has been stripped of her British citizenship, but lawyers are planning a legal challenge to overturn the decision.

Details of Miss Begum’s alleged role in Isil have come from two separate sources, including anti-Isil activist group Sound and Picture, whose members lived under the jihadists’ rule and closely followed its members. Some of the information has been confirmed by Western intelligence, which is understood to be looking into the allegations as part of a criminal investigation.

According to Sound and Picture, Miss Begum arrived in Syria after crossing the Turkish border in February 2015. She was then taken, along with two other Bethnal Green schoolgirls, to the central city of Raqqa, which had become the capital of Isil’s self-declared caliphate.

They were then sent to a “madhafa” or guesthouse for single women, where Miss Begum was married off to Riedijk.

According to the activists she then enrolled in al-Tala’ia camp just south of the Euphrates River in Raqqa province, where she stayed for three months receiving “military and religious training.”

After that, she, Amira Abase and Kadiza Sultana, are said to have graduated to the Khansaa Battalion, a notorious all-female “police squad” which had other British members in its ranks, including Muslim convert Sally Jones.

Miss Begum is then alleged to have worked for several months in al-Hisba, Isil’s religious enforcement unit. Most of the women in the Hisba took up roles on a voluntary basis and the position gave them an elevated status within the “caliphate”.

“There were lots of young European women in the Hisba,” Aghiad al-Kheder, an activist from Deir Ezzor who founded Sound and Picture, told The Telegraph. “Some of them were very harsh and the local population became very scared.”

He said Miss Begum carried a Kalashnikov rifle and had a reputation for being strict on women she thought were behaving in a “non-Islamic” way, according to Isil’s punitive rules.

“Members of our group from Raqqa knew her well,” said Mr Kheder. “If you get the chance to interview her again you can ask her about an incident that happened in al-Amassi Street in Raqqa in 2016, when she was with the Hisba.

“She shouted at a civilian woman wearing brightly coloured shoes and told her that was ‘haram’, or not permissible, as this would attract the attention of men. The woman said to her, ‘so why is it ok for you to wear coloured shoes?’ Shamima was herself wearing white and pink trainers.

“She will remember this,” he said.

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He believes that in her role, which paid somewhere between £500-£1,500 a month, she likely ordered the imprisonment and lashing of local women in Raqqa who were deemed not to be observing its dress code or were caught travelling without a male guardian.

During her time in Isil, she is also thought to have been actively trying to recruit other young women across Europe.

The Telegraph has been shared messages reportedly sent by Miss Begum to a number of girls, including a teenager from Austria in mid-2015.

She used the pseudonym “Umm Asma” online before later changing it to “Umm Ahmed” (meaning Mother of Ahmed).

“Don’t believe any of the bad things you hear about Dawla (the State), it’s fake. You have everything you want here,” she told one of the girls. “And we can help find you a good-looking husband.”

In February 2016, she was left alone briefly after her husband Riedijk was arrested and jailed by Isil for attempting, with a group of other Dutch fighters, to set up a breakaway battalion following disagreements with some of its Emirati leaders in the Diriyah area of Raqqa.

However, he was released a few weeks later and accepted back by the group.

Miss Begum and Riedijk moved from Raqqa to Deir Ezzor in early 2017 just as the city was coming under assault from Western-backed Syrian Democratic Forces (SDF), and while she was pregnant with their first child.

It was after the birth that she was said to have transferred from the Hisba to the women’s “military police”, remaining with them, Mr Kheder said, “until the end”.

Experts say it was not uncommon for foreign women to have played active roles in Isil beyond that of housewife, such as joining the Hisba and receiving defensive military training.

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“Due to the secondary role they played in the group’s propaganda, it is always harder to find documentation to prove they picked up arms or committed crimes compared to their male counterparts,” Devorah Margolin, a senior research analyst at the War Studies Department of Kings’ College London who specialises in women’s role within Isil, told The Telegraph.

She said it was often these women who were the most ideologically driven.

The couple was among the last to leave Isil territory, counting themselves among the most hardcore supporters of the group. Miss Begum admitted she had opportunities to leave but did not take them.

She said she “respected” the decision made by Miss Abase and a fourth London schoolgirl, Sharmeena Begum, to stay, saying she only surrendered out of concern for her unborn baby.

Miss Begum said the two were still alive when she left the final pocket of Baghuz, which fell in March. However, their names are not on recent camp registration documents seen by The Telegraph, raising the prospect they may have been killed in fighting.

Miss Begum said in her first interview that she did not regret joining Isil, in part because it meant she got to meet Riedijk, but in later interviews became more remorseful.

She begged the British authorities to rescue her from the refugee camp in northern Syria where she gave birth to her third child, Jarrah, who later died from a lung infection.

But instead, her citizenship was revoked by Sajid Javid, the Home Secretary. It is thought Mr Javid did not consult either the attorney general or the solicitor general before making his decision, something that could leave him vulnerable in the event of a legal challenge.

Counterterrorism police are now trying to build cases against many of the Britons in the eventuality they are allowed home.

The UK and many other countries have been reluctant to take back foreigners who joined Isil, in part due to fears that it would be difficult to obtain the evidence to successfully prosecute those individuals for crimes committed abroad, said Ms Margolin.

“That being said, proving that Shamima Begum joined the Hisba would not only poke holes in her story of being just a housewife,” she added, “but would be the first step needed to create a solid case against her that would hold up in court.”