The Isis fighter known as Jihadi Jack has been stripped of his British citizenship, prompting a diplomatic row between the UK and Canada, it has been reported.
Muslim convert Jack Letts, 24, who had held dual UK and Canadian citizenship, declared he was an "enemy of Britain" after travelling from Oxfordshire to Syria at the age of 18 to join the terror group.
He has begged to be allowed to return to the UK, insisting he had "no intention" of killing Britons, after he was captured by Kurdish forces in 2017.
The Home Office has now stripped Letts of British citizenship, meaning he is the responsibility of the Canadian government, The Mail on Sunday said.
It was reportedly one of the last actions of Theresa May’s administration.
The decision is understood to have angered officials in Ottawa, prompting fears of a row between Canadian PM Justin Trudeau and Boris Johnson when they meet at the G7 summit in France next weekend.
Letts, who travelled to the Middle East in 2014, is now among more than 120 dual nationals who have been stripped of their British citizenship since 2016, including Isis bride Shamima Begum.
Ms Begum was one of three girls from Bethnal Green, east London, who left the UK aged just 15 in February 2015 and travelled to Syria to join Islamic State. It was thought Ms Begum may have a claim in Bangladesh because of her family background, something Bangladeshi officials denied.
The move can only be made against people with two passports, because international law prevents the Government from making anyone "stateless".
It will come as a blow to Lett's parents, Sally Lane and John Letts, who were found guilty at the Old Bailey in June of funding terrorism and given 12-month sentences suspended for 15 months.
In an interview after their conviction, they said: "Jack is still a British citizen and we have pleaded with the Government to help us to bring him to safety, even if that meant that he might be prosecuted in the UK."
A Home Office spokesman said: "This power is one way we can counter the terrorist threat posed by some of the most dangerous individuals and keep our country safe."
In an interview with ITV earlier this year, Letts said he felt British and that he wanted to return to the UK, but admitted he did not think that would be likely.
"I'm not going to say I'm innocent. I'm not innocent. I deserve what comes to me. But I just want it to be... appropriate... not just haphazard, freestyle punishment in Syria," he told the broadcaster.
Struggling with obsessive compulsive disorder and Tourette's when he was at school, Jack converted to Islam at the age of 16.
He used to attend the Bengali mosque in Cowley Road, Oxford, before he came into contact with men with a more radical ideology.
Jack has previously admitted he was at one time prepared to carry out a suicide attack, telling the BBC: "I used to want to at one point, believe it or not. Not a vest. I wanted to do it in a car. I said if there's a chance, I will do it."
He also said in the interview, which took place in October last year but was not broadcast until after his parents' trial had ended, that he realised he had been "an enemy of Britain" but added that he had made "a big mistake".