The assassination of Jihadi John was “personal” and not a strategic goal, spy chiefs have admitted as they detailed the painstaking methods used to catch him.

Robert Hannigan, a former director of GCHQ, revealed that vein-recognition technology and voice analysis led the security services to identify Mohammed Emwazi “within hours” of a video depicting his masked face and crucially, his hands, emerging on social media.

"We had a race to find out who he was — his size, his hands, but, above all, his voice, made identifying him quite easy," he said.

The hunt for the Isil killer, who was raised in London, began immediately, yet the drive to catch their target was borne more from a personal desire to win the propaganda war than the inherent fight against extremism.

Emwazi was not deemed a "significant military target" and as such, his death was deemed more of a symbolic victory. Mr Hannigan acknowledged that someone else would quickly step into Emwazi's shoes.

“It would have been strange to see this as a massive breakthrough,” he said. “The (Isis) threat went on.”

Douglas Wise, who helped oversee the CIA's Middle East operations, added: "If you look at Emwazi as an adversary, he certainly wasn't a glorious battlefield commander.