A British national, who goes by the name of John and is believed to have decapitated American journalist James Foley, is the leader of a group of three U.K.-born militants in charge of holding foreign hostages for the Islamic State in Syria, according to a report. The three Britons are reportedly referred to as “the Beatles” by their hostages because of their nationality.

A former hostage, who was held for a year at Raqqa, described the British executioner as intelligent, educated and a devout believer in radical Islamic teachings, the Guardian reported. Following Foley's gruesome killing depicted in a video released Tuesday, an international manhunt by the FBI, MI5 and Scotland Yard was taken up Wednesday to hunt down the identity of the English-speaking Islamist militant. The man is reportedly likely to be on police radars for past criminal behavior for his involvement in jihadi activities overseas.

John is believed to be from London and was reportedly the main ISIS negotiator during talks held earlier this year, which saw 11 hostages released to Turkish officials after the extremist Sunni militant outfit's ransom demands were met. He was also recognized by several sources in Syria as the main negotiator in Raqqa from where he is said to have held discussions with the families of several hostages over the Internet, according to the Guardian.

A linguistics expert at the University of York, Paul Kerswill, said he believed John spoke in "multicultural London English" commonly found in London's East End.

"He probably has a foreign language background but it sounds like multicultural London English, which is people from all kinds of backgrounds who mix in the East End, a new kind of cockney," he said.

Claire Hardaker, a linguistics expert at Lancaster University, told the Guardian: "We're definitely looking at a British accent, from the south, and probably from London, Kent or Essex."

An English-speaking militant was deliberately chosen to front the video to cause maximum impact in the West, Peter Neumann of King's College London, reportedly said.

“This is significant because it signifies a turn towards threatening the west. They are saying we're going to come after you if you bomb us," he said, adding: "It's not significant that British fighters have been beheading and torturing because that's been happening for a year and a half. The significant thing is that this was an American and was connected to a direct message that 'we are targeting you'."

Afzal Ashraf of the Royal United Services Institute told the Guardian that the video could prove useful for recruiting Western extremists.

"The message that really motivates people is it's a way of hitting back at what they perceive to be the US bullying and domination of the Muslim world. They feel impotent when they see the awesome US air and land power and they see this as a way of hitting back and that's the principle motivation," he reportedly said.

For months, U.K.’s security services have warned of the sheer number of its citizens leaving the nation's cities to join the call to jihad in Syria and Iraq. About 500 Britons, 700 Frenchmen and 500 Belgians are believed to be fighting on the frontlines of the war-torn region.