44 year old aid worker David Haines was abducted in Syria in 2013 and was held captive by ISIS militants who already killed two US journalists.
The Foreign Office in a statement said,"All the signs are that the video is genuine".
The video had indications that the militants will also kill a second hostage Alan Henning. Cameron, however, vowed to find the killers in whichever way possible.
Chairing a meeting with th Emergency Committee Cobra early on Sunday, Ccameron issued a statement saying that the killings would not change Bri
tain's stance against the ISIS.
He further said,"It is an act of pure evil. My heart goes out to the family of David Haines who have shown extraordinary courage and fortitude throughout this ordeal," he said. "We will do everything in our power to hunt down these murderers and ensure they face justice, however long it takes."
He also called Haines a "National Hero".
[Read more in ibnlive.in]