Shamima Begum’s potential return to the UK to challenge the deprivation of her British citizenship has been put on hold after the Government was given permission to take the case to the Supreme Court.

Ms Begum, now 20, was one of three east London schoolgirls who travelled to Syria to join the so-called Islamic State group (IS) in February 2015.

She lived under IS rule for more than three years before she was found, nine months pregnant, in a Syrian refugee camp in February last year.

Then-home secretary Sajid Javid revoked her British citizenship on national security grounds later that month.

Earlier this month, the Court of Appeal ruled that “the only way in which she can have a fair and effective appeal is to be permitted to come into the United Kingdom to pursue her appeal”.

Lord Justice Flaux – sitting with Lady Justice King and Lord Justice Singh – said: “Fairness and justice must, on the facts of this case, outweigh the national security concerns, so that the leave to enter appeals should be allowed.”

The judge also found that “the national security concerns about her could be addressed and managed if she returns to the United Kingdom”.

At a remote hearing on Friday, the Government argued that the Court of Appeal wrongly concluded Ms Begum should be granted leave to enter the UK despite the fact that “she is assessed to pose a threat to UK national security”.

Sir James Eadie QC, for the Home Office, told the court there were “significant national security concerns” about Ms Begum’s potential return to the UK.

He said: “The exposure of the public to an increased risk of terrorism is not justifiable or appropriate in an individual case on fairness grounds save perhaps in the very rarest of cases … this was not such a rare case.”

Sir James added: “The public will be less well protected if Ms Begum returns than it would be if she does not return.”

He argued that the case concerned “an issue of real pressing public importance” which was “perhaps the central democratic issue of our times”, namely what the courts should do when “someone at present cannot have a fair and effective hearing in a deprivation appeal, but they cannot do so because … of going abroad and aligning with terrorist groups”.

Sir James also said: “This cannot be assumed to be unique or even, given the number of people who have aligned in this way, to be a highly unusual case.”

Lady Justice King said the case raised “points of law of general public importance” which should be considered by the UK’s highest court.

She said that “clearly there must be a stay” on Ms Begum’s potential return to the UK “until further order by the Supreme Court”.

The judge also granted permission for Ms Begum’s lawyers to challenge the decision that the absence of a fair and effective appeal did not mean her British citizenship should be restored, subject to the Supreme Court accepting that part of the case.

A Home Office spokeswoman said: “We are pleased that we have been able to secure permission to have the Supreme Court consider our appeal.

“It would not be appropriate to comment further whilst legal proceedings are ongoing.”

On Friday, the court also heard that the Court of Appeal’s draft judgment “or the essential contents of that judgment” was apparently leaked to The Sun ahead of its formal publication earlier this month.

Lady Justice King said that the article reporting the court’s decision – which was taken down before the judgment was delivered on July 16 – “rightly or wrongly referred to ‘senior Government sources’ as having been the source of the information”.

The judge added: “We intend to report that matter to the Attorney General.”

Sir James told the court that Sir Jonathan Jones, the head of the Government Legal Department, was conducting an investigation into the leak and would provide a final report in two to four weeks.

Ms Begum’s barrister Adrian Waterman QC said in written submissions: “The content of The Sun article lends itself to the inference that the Government sources referred to were seeking to strike first in the media, thus setting the agenda in a way which was unsympathetic to (Ms Begum) at a time when there would be no opportunity for any balancing comment to be included.

“In addition to being a contempt of court, the draft judgment had contained information taken from a witness statement … which was covered by a confidentiality order.”

Mr Waterman said the information was “sensitive and could expose (Ms Begum) to real harm if made public”, which he said was “obviously a matter of very real concern”.

Ms Begum was one of three schoolgirls from Bethnal Green Academy who left their homes and families to join IS, shortly after Sharmeena Begum, who is no relation, travelled to Syria in December 2014.

Kadiza Sultana and Amira Abase, then 16 and 15 respectively, and Ms Begum boarded a flight from Gatwick Airport to Istanbul, Turkey, on February 17 2015, before making their way to Raqqa in Syria.

Ms Begum claims she married Dutch convert Yago Riedijk 10 days after arriving in IS territory, with all three of her school friends also reportedly marrying foreign IS fighters.

She told The Times last February that she left Raqqa in January 2017 with her husband but her children, a one-year-old girl and a three-month-old boy, had both since died.

Her third child died shortly after he was born.