It is thought the spies are not British citizens, but have been executed for working for the coalition and providing photos and videos from inside Raqqa, The Independent reported.
Speaking to the camera, the masked gunman can be heard saying: "This is a message to David Cameron," who he describes as an "imbecile" and "slave of the White House."
Read alsoDaily Mail reports on double life of Russian 'spy' beheaded by ISISThe militant compares the Prime Minister to "arrogant and foolish" predecessors Gordon Brown and Tony Blair, and concludes : "You will lose this war, as you lost in Iraq and Afghanistan.
The video, which cannot be independently verified, ends with a trailer for a further execution and a brief clip of a young child, wearing militant garb and speaking with a British accent, appearing to say: "We will kill the kuffar [non-believers] over there."
Read alsoIraqi army declares first major victory over Islamic State in RamadiMiddle East analysts have reported a sharp increase in the number of propaganda videos released by ISIS after its loss of the Iraqi city of Ramadi.
A mixture of old and new footage, the flurry of activity has been seen as an attempt to distract from that significant defeat.
