The 11-minute footage, which was released by the Isis media wing, includes a “message for David Cameron”, read by a masked man with a British-sounding accent who threatens attacks in the UK.
Standing behind five kneeling hostages in orange jumpsuits, the unknown extremist repeatedly points a gun at the camera while claiming to be preparing an invasion of Isis fighters in Europe.
The video then appears to show the murder of the hostages, who allegedly “confess” to having completed reconnaissance missions that were sanctioned by British authorities.
In a seemingly deliberate emulation of Isis videos featuring the British extremist Mohammed Emwazi, the footage focuses on one man wearing a balaclava and repeatedly addressing the prime minister directly.
Gesticulating in a manner similar to that used by Emwazi, aka Jihadi John, the unnamed terrorist repeatedly waves a gun at the camera as he references British airstrikes in Syria.
On Sunday, UK security agencies began the hunt for what appears to be a Briton in the Isis video.
British investigators do not yet know the identity of the man taunting Cameron and making threats directed against the UK. They saw the video for the first time along with the rest of the world.
A Foreign Office spokesman said the video was “Daesh propaganda”, using another name for the terror group, and added that the government was examining its content.
Investigators have no way of authenticating the video but are working on the assumption that it is real. The man, in addition to delivering an anti-British tirade, gives the impression that he was also involved in the execution, but the footage may have been edited. He does not appear to have a regional or working-class accent.
The young boy in the video is not necessarily British and could easily be a Syrian or Iraqi who picked up some English.