Mohammed Reza Haque appears in the newly released video dressed in black and using a hunting knife to cut the head off a bound and kneeling captive, the Mail on Sunday reported.
Haque was a close associate of Choudary, Britain’s most notorious hate preacher, who was jailed in September for five years and six months for drumming up support for Islamic State of Iraq and the Levant (Isil).
Haque, from Bethnal Green, East London, was photographed and filmed in countless UK demonstrations with Choudary and acted as his bodyguard.
The latest Isil video shows the execution of five men accused of spying for the New Syria Army (NSA), a British and US-backed group of Syrian rebels.
The video released by the militants’ Amaq media wing, shows the men wearing Guantanamo-style orange jumpsuits and apparently confessing to spying for the NSA, followed by their executions.
The victims are denounced apostates who disbelieved and fell into apostasy, and championed the Crusaders and helped them against Muslims.
They thought they were safe, but God shamed them, and they will be slaughtered by this knife which will slaughter those like them.
Counter terror sources confirmed Haque is in Syria and said they were investigating the video.
Dr Shiraz Maher, an Isil expert at the department of war studies at King’s College, London, told the newspaper: Some people dismissed the radical network that surrounded Anjem Choudary as clownish.
Yet scores of individuals, like Haque, from that cluster have travelled to Syria from Britain and now pose a very significant security risk. They’re not there to take a back seat.