The third Briton who speaks in a recruitment video circulated by militant group Isis is an Aberdeen man called Abdul Raqib Amin, once better known locally for fighting, drinking alcohol and frequenting nightclubs, it has been revealed.

In the video, "There Is No Life Without Jihad", Raqib says: "Are you willing to sacrifice the fat job you've got, the big car you've got, the family you have? Are you willing to sacrifice this for the sake of Allah? Definitely! If you sacrifice something for Allah, Allah will give you 700 times more than this."

It is believed that Raqib - who in the video is introduced as "Brother Abu Bara' al Hindi" - was born in Bangladesh before moving to the Scottish town, where he soon acquired a reputation for being a trouble-maker, an acquaintance told the BBC.

"He was a bit arrogant," says the man, speaking anonymously. "A bit (of) aggro, maybe something to prove. He ended up in a lot of fights. To learn he's accepted religion in such an extreme way is a bit shocking. Shocking because he's a youth from Aberdeen who's ended up somewhere like that."

However another friend told Sky that Raqib had calmed down recently. "He was more of a lad than a regular attendee at the mosque. He was a happy guy, played football - he was a good player and he supported Aberdeen. I remember him as a hyper person, energetic and loud... not the type of person you'd expect to go and do this."

The two other men in the video have been identified as Nasser Muthana and Reyaad Khan from Cardiff. It is unclear how many British-born Jihadists are now in Syria and Iraq. MI5 estimate around 500 but Birmingham Khalid Mahmood MP believes the true figure is much higher. "I imagine 1,500 certainly would be the lower end," he told Sky News. "If you look across the whole of the country, there's been a number of people going across."

Commentators have put forward a number of reasons for why so many young men from apparently safe, secure backgrounds are willing to risk their lives fighting for the Islamist cause. Towards the end of the video Raqib seems to give one possible explanation: "All my brothers living in the west, I know how you feel. When I used to live there, in the heart you feel depressed. The cure for the depression is Jihad."