Speculation is rising that a masked man narrating a new ISIS execution video could be a Walthamstow jihadi who fled to Syria, a report has claimed.

Father-of-four Siddhartha Dhar, 32, also known as Abu Rumaysah al Britani, travelled to the Middle East in September 2014 after he was accused of inciting terrorism.

Now, it is thought that Dhar may be the narrator and potential executioner in a propaganda video showing the killing of five men alleged to have been spying on the extreme Islamist group for the United Kingdom.

In the video, the masked man threatens David Cameron and warns of possible attacks in the West.

Speaking to the Daily Mail, terror expert Raffaello Pantucci, director of international security studies at Royal United Services, said the narrator sounds “very similar” to Dhar.

He said: “He sounds a bit like Abu Rumaysah from Al-Muhajiroun videos.

“From watching him in Al-Muhajiroun videos and this new video he sounds very similar.

“The masked man sounds like he is from London.

“ISIS is full of people who are from all over the place, but he seems educated, given he uses the word ‘imbecile’ a number of times.”

Dhar was a supporter of the banned group Al-Muhajiroun, which praised the September 11 attacks, and radical preacher Anjem Choudary.

A former bouncy castle salesman, Dhar has posted photographs online showing him posing with a new born son and an automatic rifle.

His sister, Konika Dhar, has said she does not believe her brother is the man in the video, but she said the voice “does sound a bit like him”.

In May last year, he also shared propaganda entitled ‘A Brief Guide to Islamic State’, encouraging people to join the terrorist group.

Security services are currently trying to identify the masked man in the new 10-minute video, which also shows a young child wearing military-style clothes and talking about killing ‘unbelievers’.