The Washington Post claims today to have identified the Islamic State executioner known as ‘Jihadi John’ as Mohammed Emwazi, a British national from west London.

Emwazi was born in Kuwait and grew up in a middle class London-based family. He graduated with a degree in computer programming from the University of Westminster and is believed to have travelled to Syria around 2012.

Friends said that he started to become radicalised after a planned safari trip in Tanzania. Emwazi and two friends were detained as soon as they landed in Dar es Salaam, and eventually deported. He claimed an MI5 officer had told authorities he intended to travel to Somalia to join Al Shabaab. He also claimed that representatives from the security agency had tried to recruit him.

Asim Qureshi, research director of group CAGE and a friend of Emwazi, said there was “an extremely strong resemblance” between Emwazi and the masked ‘Jihadi John’ is the various ISIS beheading videos. “This makes me feel fairly certain it is the same person.”

Another friend, who did not want to be identified, said: “I have no doubt that Mohammed is Jihadi John. He was like a brother to me… I am sure it is him.”

Qureshi provided a series of emails between himself and Emwazi which show that after his detention in Dar es Salaam, he decided to move back to Kuwait, his country of birth, where he landed a job with a computer firm. On a return trip to Britain in 2010, however, counter-terrorism officials detained him and prevented him from returning to Kuwait.

He wrote in an email: “I had a job waiting for me and marriage to get started,” adding: “I feel like a prisoner, only not in a cage, in London. A person imprisoned & controlled by security service men, stopping me from living my new life in my birthplace & country, Kuwait.”

Another friend said that Emwazi was by that stage desperate to leave Britain and settle permanently in the Middle East: “He at some stage reached the point where he was really just trying to find another way to get out.”

A former hostage said that Jihadi John was part of a team of three men with British accents who were guarding a group of Western hostages. The hostage said that another of the men, nicknamed “George” was the ringleader while Jihadi John was more quiet and intelligent.

Early last year the hostages were moved to Raqqa, the de facto capital of the Islamic State, where they were often visited by the three men, who by then appeared to have been given more senior roles in the regime.

Jihadi John has killed numerous hostages in Islamic State videos, including American journalists James Foley and Steven Sotloff, British aid workers David Haines and Alan Henning and American Muslim convert Peter Kassig.