Shamima Begum, the woman who left Britain as a schoolgirl to join Islamic State in Syria, has lost the initial stage of her appeal against the Home Office’s decision to revoke her UK citizenship.

A unanimous judgment by the Special Immigration Appeals Commission (Siac) found against Begum, now 20, on three preliminary grounds, including that she had not been improperly deprived of her citizenship. The judgment prevents her from returning to London.

The ruling accepted that conditions in al-Roj camp, where she is being held in Syria, amount to, at least, cruel, inhuman and degrading treatment, but deemed that her human rights were not protected under UK law. Her lawyers announced they would appeal immediately.

Mrs Justice Elisabeth Laing, Mr Doron Blum and Mr Roger Golland concluded that the decision to strip Begum of her citizenship did not make her stateless because she was entitled to, or in effect held, Bangladeshi citizenship. She could, nonetheless, continue with her substantive appeal.

The Siac judgment said: “We accept that, in her current circumstances, [Begum] cannot play any meaningful part in her appeal and to that extent, the appeal will not be fair and effective.”

However, it went on, parliament intended that the home secretary “should be free to make a deprivation order immediately after giving notice of intention to deprive the person concerned her citizenship, whether or not the person concerned wishes to … appeal against the notice”.

The ruling said that when she was stripped of her UK citizenship, Begum “was a citizen of Bangladesh by descent, by virtue of [Bangladeshi nationality legislation]. She held that citizenship as of right. That citizenship was not in the gift of the [Bangladesh] government and could not be denied by the [Bangladesh] government in any circumstances.”

Mrs Justice Laing said Begum had no protection under the European convention on human rights – including the right to life or prevention of torture – because she was in Syria and therefore beyond its reach. The home secretary, she explained, was “only obliged to consider risks which are foreseeable and which are a direct consequence of the decision to deprive a person of his nationality”.

The judgment accepts that conditions in al-Roj camp in Syria “would breach [Begum’s] rights under article 3 [of the convention, which bans torture, inhuman or degrading treatment] if article 3 applied to her case”.

Begum’s lawyers alleged she had been left stateless and unable to mount a “fair and effective” legal challenge and was at risk of “death, inhuman or degrading treatment”. If forced to go to Bangladesh, her parents’ country of origin, she could be hanged, they told the tribunal at a partially secret hearing last October.

Begum was born in the UK and grew up in east London. The court heard there was no evidence she had ever visited Bangladesh or applied for citizenship there.

In February 2015, aged 15, Begum left her home with two other teenagers, Kadiza Sultana, then 16, and Amira Abase, then 15, and travelled to Syria to join Isis. She was found, nine months pregnant, in a Syrian refugee camp in February 2019. The then home secretary, Sajid Javid, stripped her of her British citizenship later that month.

Begum claims she married the Dutch Isis fighter Yago Riedijk 10 days after arriving in Isis territory, with her schoolfriends also reportedly marrying foreign fighters in the terrorist group.

The couple had three children, two of whom died of disease or malnutrition during the terrorist group’s last stand at Baghuz. The third died in al-Hawl camp.

The Home Office welcomed the Siac judgment, saying: “It would be inappropriate to comment further whilst legal proceedings are ongoing.”

Begum’s solicitor, Daniel Furner of Birnberg Peirce, said she would “immediately initiate an appeal [against] Siac’s decision … as a matter of exceptional urgency”.

Furner added: “The stark reality of her situation was brought before the court last year as a matter of exceptional urgency – how could she in any meaningful and fair way challenge the decision to deprive her of her nationality, a young woman in grave danger who had by then lost her three children?

“The judgment will be hard to explain to her. The logic of the decision will appear baffling, accepting as it does the key underlying factual assessments of extreme danger and extreme unfairness and yet declining to provide any legal remedy.

“Now, in February 2020, the dangers Ms Begum faces have increased; her chance of survival even more precariously balanced than before.”

Maya Foa, the director of the human rights group Reprieve, said: “The court today found that the detention conditions of British nationals in north-east Syria constitute torture or cruel, inhuman and degrading treatment. It is rank hypocrisy for the government to abandon British families to torture, which it professes to categorically oppose. The only just solution is for the government to repatriate British families, and to try people in British courts if they have charges to answer”.

Clare Collier, Liberty’s advocacy director, said: “The fact the government has left a young woman effectively stateless shows how little regard it holds for fundamental rights.

“Shamima Begum should not be banished – banishing people belongs in the dark ages, not 21st-century Britain. This case is just one example of how quickly ministers use citizenship-stripping when they could use other powers.

“It’s clear why they use these archaic banishments and that is to score political points and look tough on terrorism. It has nothing to do with making the public safe.

“In fact, this leaves us less safe as services are unable to conduct proper investigations that could help prevent young people, like Shamima, from entering terrorist circles in the future.”