LONDON — Shamima Begum, a woman who traveled to Syria from London as a schoolgirl to join ISIS, should be allowed to return to appeal the government’s decision to strip her of her British citizenship, a court ruled on Thursday.
The Court of Appeal ruled that the only way Ms. Begum would be able to pursue a “fair and effective appeal” was “to be permitted to come into the United Kingdom.”
Ms. Begum, now 20, spent years in Islamic State territory, but fled to a refugee camp in northeastern Syria after the group lost control in the region, and had expressed a desire to return to Britain.
Her case is a prominent example of the challenges many Western governments face with citizens who joined the group, and who some argue would pose a national security threat if repatriated.
Through a spokesman, the British Home Office, the government department responsible for migration and security, said it would appeal what it called “a very disappointing decision.” Ms. Begum’s lawyer, Tasnime Akunjee, praised the court’s ruling, writing on Twitter, “Good sense prevails.”
Ms. Begum first made headlines five years ago, when she and two classmates, who came to be known as the Bethnal Green girls after the neighborhood in London where they had lived, boarded a flight to Turkey and then traveled to Syria to reach territories of the Islamic State at a time when the terrorist organization was at the height of its power.
Ms. Begum married a young Dutch fighter weeks after her arrival and later gave birth to three children. All have since died.
In February last year, a British journalist located Ms. Begum in Al Hol refugee camp in northeastern Syria, where the families of thousands of Islamic State fighters had fled. She told the reporter that she was “willing to change,” and asked the authorities “to re-evaluate my case, with a bit of mercy in their heart.”
But that same month, her family was informed that she would be stripped of her British citizenship, the only citizenship she has, in a letter from Sajid Javid, then the country’s home secretary.
Despite concerns that this would render Ms. Begum stateless, British law allows the home secretary to revoke the citizenship of a single nationality holder if there is “reasonable ground” to believe that the person can acquire another citizenship elsewhere.
Ms. Begum appealed, but a special tribunal ruled the decision was lawful because she was “a citizen of Bangladesh by descent” from her mother, who is a citizen of the South Asian nation. Since then, she has pleaded with the British authorities to repatriate her to stand trial in her home country, something the government has vowed never to do.
The authorities in Bangladesh have said that Ms. Begum never claimed citizenship of that nation and that she would not be allowed in Bangladesh.
The ruling that Ms. Begum is entitled to return to Britain to appeal the decision on her citizenship does not mean that she will be successful in having it restored, however.
The case will be reviewed by the special tribunal that initially ruled that removing Ms. Begum’s citizenship was lawful.
But those opposed to Ms. Begum’s return to Britain say her repatriation for the citizenship appeal could pave the way for her to remain in the country indefinitely, as it is unlikely she would be sent back to a detention camp in northeastern Syria.
“If Ms. Begum does come back to this country, it will prove impossible to remove her,” Mr. Javid, the former official who stripped Ms. Begum of her citizenship, said in a statement.
Mr. Javid said her presence in Britain would create a “national security risk that cannot be fully mitigated.”
Governments in Britain, France and other countries have so far refused repatriation in most Islamic State-linked cases, taking back only some children and families on a case-by-case basis. A growing chorus of academics, psychologists and rights organizations have urged the authorities to repatriate their citizens, citing appalling conditions in refugee camps and detention centers, and a right to be given a fair trial at home.
About 900 children from Western nations — including Australia, Belgium, Britain and France — have spent years in limbo in camps in Syria.
But the authorities have struggled to outline a comprehensive policy for ISIS detainees and their families.
Shiraz Maher, the director at the International Center for the Study of Radicalization and Political Violence at King’s College London, said in a Twitter post that many governments worried that trying ISIS sympathizers at home could result in acquittals or minimal sentences, because of the challenge of gathering evidence.
In several countries, including Britain and France, defendants can be convicted of joining a terrorist organization if they traveled to a territory controlled by an extremist group. Yet dozens of people convicted of such crimes are expected to be released in the coming years, raising fears that they could plan or carry out attacks.
“The danger is that you can’t secure a proper conviction against them,” Mr. Maher said on Twitter. “Then you have these people walking our streets, which is unfathomable. Or you secure a conviction on a lesser charge and they’re out in a few years.”