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 IS and has left their territory and is now being held by Kurdish forces fighting the group.
Letts spoke to the BBC via text and voice messages.
Speaking about leaving IS territory, Letts said: "I found a smuggler and walked behind him through minefields."
He said he is now in solitary confinement in a jail in Kurdish-held north-east Syria.
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 IS- 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 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. "I realised they were not upon the truth so they put me in prison three times and threatened to kill me."
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.
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 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.
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.
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