Jack Letts from Oxford, dubbed "Jihadi Jack", is suspected of going to Syria to fight for so-called Islamic State.
But he claims he is opposed to ISIS and has left their territory and is now being held by Kurdish forces fighting the group.
Jack Letts spoke to the BBC via text and voice messages.
Speaking about leaving ISIS territory, Jack Letts said: "I found a smuggler and walked behind him through minefields."
He said he and the smuggler "eventually made it near a Kurdish point where we were shot at twice and slept in a field".
He said he is now in solitary confinement in a jail in Kurdish-held north-east Syria.
Jack Letts converted to Islam while at Cherwell comprehensive school in Oxford.
He travelled to Jordan, aged 18, in 2014, having dropped out of his A-levels. By the autumn of that year he was in ISIS controlled territory in Syria.
His family deny he went there to fight and instead say he was motivated by humanitarian reasons.
He married in Iraq and now has a child.
He said that he had been injured in an explosion and had gone to Raqqa, the de facto capital of ISIS in Syria, to recuperate.
He claimed he became disillusioned with the group about a year ago after it killed its former supporters.
"I hate them more than the Americans hate them," he said.
He claimed he had escaped from low-security detention and had been in hiding when he managed to find a people smuggler to take him out.
His parents have pleaded not guilty to charges of funding terrorism after being accused of sending cash to their son.
John Letts and Sally Lane told the BBC that, having not heard from their son for several weeks, they suddenly received a message saying he was in a safe zone.
"It was the news we've been waiting for for three years ever since he went out there - and now we just want to get him home," said Ms Lane.
They believe their son is not being treated badly but are concerned about his mental health.
Letts' parents are calling on the British authorities to do "whatever they can" to help him.
The government had told them that they could only help if he left ISIS territory but now he is out "no-one wants to take responsibility", said Ms Lane.
John Letts, an organic farmer, acknowledges that his son "will have to account for his actions" once he returns to Britain, but the family is not convinced "he has done anything at all", from what he has told them.
The UK government advises against all travel to Syria and parts of Iraq and a number of people who returned from these areas have been prosecuted.
Asked by the BBC why the UK government should help him, Jack said: "I don't want anyone to help me."
"I'll just chill here in solitary confinement till someone decides it's easier to kill me," he added.
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