Jamie Read, 24, and James Hughes, 26, gave an exclusive interview to The Sun in which they recounted their experiences fighting against the terror group and their motivations for travelling to the region.

"Killing the aid worker was the final straw," said Read. "There is no justification for their executions – for putting innocent guys on their knees and doing that.

Henning, a taxi-driver from Salford, Manchester, was kidnapped while delivering aid for a charity in Syria and was executed on camera by the terror group in October.

"My family were nervous and obviously worried about my well-being – we have gone into an unknown world. But I'm a firm believer that if you want to do something you have to do it and not just talk about it."

Hughes, an ex-soldier from Reading, said: "I wanted to help. The situation in England is getting bad in terms of the support IS get. The world needs to open its eyes to the threat they pose."

The pair flew from Manchester to Istanbul before moving on to Erbil, the capital of the semi-autonomous Kurdistan region in northern Iraq, and then driving in a convoy to a location 360 miles east of the besieged city of Kobani, IBTimes reported.

Despite being termed mercenaries, the pair say that they are not receiving any money for their efforts, only food and equipment.

"We funded this out of our own hard-earned money. We had a spare bit of money but that has all gone now," said Read.

The pair also described what they have seen while fighting alongside the Kurdish forces, claiming that both ISIS and the Kurds have basic fighting strategies in comparison to their time in the British army.

"Forget about any Western tactics," said Read. "There's no reconnaissance, no intelligence work done and no logistics. The first thing we did was to push forward into no man's land and put an observation post there."

They also spoke of villages destroyed by the terror group following an offensive which has seen them capture large swathes of land across Iraq and Syria.

"We have seen villages that have been ransacked by ISIS forces. They are ghost towns. People have fled or been killed. All you see is wrecked buildings."

While the pair are the first two known British nationals to join the fight against ISIS on the ground, official figures estimate that more than 500 British nationals have travelled to Syria and Iraq to fight for the terror group.

Today, two young British nationals, including one of Pakistani descent, who spent eight months fighting alongside an al Qaeda-linked terror group in Syria, were jailed for 12 years and eight months each.

The pair were arrested at Heathrow airport in January after returning from Syria. Both men pleaded guilty in July, The Economic Times reports.

Yusuf Zubair Sarwar and Mohammed Nahin Ahmed, both 22, from Handsworth in Birmingham, travelled to Syria in May 2013 after contacting extremists.

Moreover, a father of two from Portsmouth has been jailed for four years for travelling to Syria to attend a terrorist training camp.

Mashudur Choudhury, 31, the first person in the UK to be convicted of terror offences in connection with the Middle East conflict, was sentenced at Kingston Crown Court in south west London, staff confirmed.

He was found guilty by a jury in May of engaging in conduct in preparation of terrorist acts, having been arrested when he arrived back at Gatwick Airport from the trip in October 2013.