The Supreme Court yesterday refused to hear an appeal against a Court of Appeal ruling which held that the revocation of Begum’s citizenship on national security grounds in 2019 was lawful.

Begum, who was born and brought up in the UK, and a British citizen from birth, left the UK at the age of 15 to travel to Syria, where she married an Islamic State fighter.

She is currently detained in a camp run by Kurdish fighters in north-eastern Syria and has spent years trying to return to the UK.

In a statement, law firm Birnberg Peirce, representing Begum, said it “will take every possible legal step, including to petition the European Court of Human Rights”.

“This is an issue that can and should, as the US urges, be resolved for all nationals by their own countries,” the firm added.

Human rights organisations have also called for Begum’s return to the UK.

Steve Valdez-Symonds, refugee and migrant rights director at Amnesty International UK, said: “It’s deeply concerning that the Supreme Court has concluded there’s no point of law to be considered on such a serious matter as stripping a British person of her citizenship — particularly when that was done on the back of her being exploited as a 15-year-old child.

“Stripping Shamima Begum’s nationality was profoundly wrong — she is and has always been British.

“Begum is now exiled in dangerous and inhuman conditions, along with thousands of other people, including women and children, in north-east Syria.

“The UK should follow others by taking responsibility for nationals stranded in Syria — including by assisting in their safe return to the UK, whether or not that means facing possible criminal investigation or prosecution on their return.”