Jihadi Jack's parents have accused former home secretary Sajid Javid of being a "coward" after he stripped their son of his British citizenship.
Muslim convert Jack Letts was 18 when he left his Oxfordshire home to join ISIS in Syria in 2014.
Letts, who held dual UK-Canadian citizenship, was jailed after Kurdish forces captured him as he tried to flee to Turkey in May 2017.
The 24-year-old's parents, John Letts and Sally Lane, said their son has been left in a "legal black hole" and the government was “shirking responsibility and passing the buck off to the Canadians”.
Mr Letts, 58, told Channel 4: “Justice doesn’t seem to be able to happen here.
“I thought British citizens had certain rights. I thought we had the right to innocent until proven guilty, the right of a trial, the right of free speech.
“It’s not us who are in denial and naive. I think it’s maybe Sajid that’s a bit of a coward and in denial and naive, and obviously it’s his last act (as home secretary) and he can move on and not have to even justify it.
“I would love to have a debate with Sajid Javid about this and see what are the reasons they’ve done this, we can’t even find out, it’s all secret.”
The Canadian government said it was “disappointed that the United Kingdom has taken this unilateral action to offload their responsibilities”.
Ms Lane, 57, said: “It was a real shock that your Government can do this to you without any form of redress or discussion or way of actually contacting Jack, given that he’s being held incommunicado and has no access to a lawyer.
“Jack and other people are now in a legal black hole.
“I think Jack wants to come back to whatever country will take him. We’ve been told by the Canadian government that they’ve been making every effort to bring him back.”
The parents were convicted at the Old Bailey in June of funding terrorism, after they sent their son £223 in September 2015.
They avoided jail after being sentenced to 15 months, suspended for a year.
Asked about the effects of their ordeal, Mr Letts added: "You don’t sleep for years. You don’t enjoy anything in your life. They’ve crushed us financially. We did what we had to do to keep our son alive and to get him free.
“We think he’s still alive, we actually have no proof of life. We know he’s been tortured.
“I want him out of his situation and I want him to face justice, if indeed he’s done something wrong. I fervently believe that he hasn’t.”
In an interview with ITV News earlier this year, Letts said he felt British and wanted to return to the UK.
Letts said: "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.”
Letts has even admitted that he was at one point 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.”
Canada's public safety minister Ralph Goodale said: "The government of Canada is aware that the United Kingdom revoked the citizenship of Jack Letts.
“Terrorism knows no borders, so countries need to work together to keep each other safe. Canada is disappointed that the United Kingdom has taken this unilateral action to offload their responsibilities.
“Investigating, arresting, charging and prosecuting any Canadian involved in terrorism or violent extremism is our primary objective. They must be held accountable for their actions.”
The UK government has revoked citizenship of a number of Britons who had left the UK to join ISIS.
Among those include Shamima Begum, after the 19-year-old from Bethnal Green turned up in a refugee camp in Syria.
Under international law, a person can only be stripped of their citizenship as long as it does not leave the individual stateless.
A Home Office spokesman said: “Decisions on depriving a dual national of citizenship are based on substantial advice from officials, lawyers and the intelligence agencies and all available information.
“This power is one way we can counter the terrorist threat posed by some of the most dangerous individuals and keep our country safe.”