Cantlie's punishment for trying to flee the extremists was so severe that the journalist almost drowned during one waterboarding session in northern Syria.

James Foley first Westerner to be murdered by Mohammed Emwazi

Both of Cantlie's attempts to escape ISIS were carried out alongside American journalist James Foley, who became the first Westerner to be murdered by the terror group's British executioner in chief Mohammed Emwazi, also known as 'Jihadi John', in a shocking filmed beheading last August, Mail Online reports.

James Foley

During one of the escape attempts, Foley, 40, actually had the chance to flee the prison but refused to take the opportunity after his friend Cantlie, 43, was caught by the guards.

The details of Cantlie's punishment were revealed by Javier Espinosa, a Spanish journalist who was held by the radical extremist between December 2013 and March last year.

Mr Espinosa, a correspondent for Spanish newspaper El Mundo, wrote in the Times: 'Foley and Cantlie tried twice. The first was a failure before it started. They were caught trying to get off their handcuffs with a skeleton key they made.

'On the second occasion, the American showed his true humanity. After getting out of the room where the prisoners were, he had to wait for Cantlie who was to escape second. The guard saw that Cantlie (had freed himself) and Foley could have tried to escape on his own, but gave himself up. 'I couldn't leave John on his own,' Foley said.

Javier Espinosa (R) his colleague Ricardo Garcia Vilanova (L) captured by ISIS between December 2013 and March last year

'The attempts by Foley and Cantlie caused them weeks and weeks of punishment. Blow after blow. Attempted drownings. More blows. 'They were literally trying to kill us for weeks until they realised that we had given up trying to escape,' Cantlie had said.'

Cantlie, who has been held captive for over two years, has appeared in multiple propaganda videos for the extremist group, often dressed in an orange jumpsuit and sat behind a desk. Meanwhile, Foley was the first of several hostages to be beheaded in a video posted online by ISIS last August.

The details of the escape attempts follow hints by Cantlie that he suffered waterboarding - a torture technique associated with America's CIA - in a propaganda video released by ISIS.

In the fifth episode of a series titled Lend Me Your Ears, released in November, he said: 'Now, unless we tried something stupid like escaping or doing something we shouldn't, we were treated well by the Islamic State.

'Some of us who tried to escape were waterboarded by our captors, as Muslim prisoners are waterboarded by their American captors.'

Cantlie last appeared in a documentary-style production titled From Inside Halab, the ancient name for the Syrian city of Aleppo, reporting on a range of topics including education, drone strikes and Sharia law.

Cantlie last appeared in a documentary-style production titled From Inside Halab

The hostage seems well in the film released last month, appearing dressed in black trousers and a brown coat, although he ominously described it as 'the last in this series'.

ISIS has posted a number of videos of hostages being murdered, including British aid workers David Haines and Alan Henning last year.