I've met many jihadists in my time as a reporter.

Among the better known were Sheikh Subhi al-Tufayli, former secretary-general of Hezbollah, Gulbuddin Hekmatyar, leader of Afghanistan's Hezb-e Islami and the now dead al-Qaeda chief, Osama bin Laden.

All were terrorists, of that there is no doubt. But whatever one thinks of their methods and grotesque manipulation of Islam's tenets, each of them, like the vast majority of their mujahideen - holy warrior - footsoldiers, were devout Muslims with a considerable knowledge of the faith under whose banner they fought.

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What then to make of reports like those recounting the arrest and charging of two British Muslims with terrorist offences after they returned to the UK from a spot of jihad in Syria. During the subsequent proceedings it was found that both had bought copies online of Islam for Dummies and The Qur'an for Dummies, to bolster their own personal understanding of the faith they say took them to the frontlines of Syria in the first place.

What can one draw too from the story of 13-year-old Younes Abaaound, a Belgian boy known to have travelled to Syria with his older brother to join the ranks of the Islamic State (IS) group. Just what can a child of this age really understand about the meaning of jihad and the horrors that await in Syria's killing fields?

As last week's barbaric killing of US journalist James Foley - beheaded at the hands of what is believed to be a British jihadist fighter from IS - garishly revealed, increasing numbers of European and other foreigners have joined the jihadist ranks and are prepared to carry out the most appalling acts in their name. The sad fact too is that most are getting younger and younger.

But just what exactly is the prime motivating factor for these young men, and women, to leave behind their families, friends and jobs to become part of a violent extremist network?

To begin with, it's important to realise that the phenomenon of European jihadist foreign fighters is not a new one. I well remember meeting some who took part in the civil war in Bosnia and later many too fought in places like Afghanistan, Iraq and Somalia.

It's important also to realise that not all those venturing to these frontlines are fully committed jihadists. Many who have travelled to places such as Libya and Syria are nationalists or non-jihadist Islamists. One young British fighter I met in Tripoli at the height of the revolution to overthrow Colonel Gaddafi's regime, far from being a jihadist, was a Muslim and Libyan nationalist.

Nevertheless, there are many full-blown jihadists among such volunteers, along with other Muslims who become heavily influenced by the jihadists they fight alongside.

In the case of Syria, the phenomenon of foreign jihadist fighters emerged after the nonviolent protests in March 2011 turned from riots into a full-blown civil war in the summer of 2011. Acres of research documents have been produced looking at the process of radicalisation that helped push European jihadis towards the battlefields of Syria and elsewhere.

Most focus on broad structural factors such as foreign policy, societal discrimination, and a lack of local leadership. But many of the same analysts that produced such studies are the first to admit the lack of work looking at the contribution to this process by what has been crassly dubbed "jihadi chic".

At its most crass and ostensibly benign this can take the form of the ISIS - Islamic State of Iraq and Syria - T-shirts or hoodies emblazoned with the group's black and white jihadist logo that are on sale in some shops and online.

Then there are those young supporters worldwide following the group's brutal exploits through its Twitter updates or even downloading a special app.

According to Thomas Hegghammer, the director of terrorism research at the Norwegian Defence Research Establishment: "Syria is probably the most socially mediated conflict in modern history, and the internet is chock full of propaganda from Syrian jihadi groups, as well as practical travel advice for aspiring foreign fighters."

While all this may sound banal, many analysts now point to the way in which these "terror brands" reinforce what some warped young men see as the "glamorous and exciting" nature of al-Qaeda or similarly inspired groups like Islamic State.

"The appeal of such movements needs to be placed within a far deeper sociological and psychological understanding of why violent action of any type can be an attractive means of action," argues Jamie Bartlett, head of the Violence and Extremism Programme and the Centre for the Analysis of Social Media, University of Sussex.

Bartlett identifies three other explanations in trying to help understand the appeal of violent extremism. The first is the way it offers a "sense of adventure" the second a "sense of personal agency" and finally the third is its ability to "win street credibility".

To some degree all these three qualities were evident in the development of British jihadist Mohammad Sidique Khan, the leader behind the 7/7 London bombings.

As writer Kenan Malik in his powerful book From Fatwa to Jihad, revealed, it was "the street" that played a crucial role in Sidique Khan's evolution into a fully fledged jihadist.

"It was not the Qur'an but crack cocaine that first led Mohammad Sidique Khan down the path to jihad. Not crack cocaine that he injected into his veins, but crack cocaine that he tried to stop others from injecting," explained Malik.

What this means is that the mainly young Asian drug dealers who had moved into the Beeston area of Leeds were dealt with by a gang called the Mullah Crew to which Sidique Khan belonged.

This group of second-generation young men, British-born of Pakistani origin, cleared many of the dealers out of the neighbourhood motivated and bonded by their mutual Islamic beliefs.

"For the Mullah Crew, Islam provided the ideas and rituals that bound its members together. What the boys found in Islam was less a theology of faith than the sacraments of street life," explains Malik.

"Friday prayers and halal meat were to the Mullah Crew what blue bandanas and British Knight trainers are to the LA Crips," says Malik explaining the significance of what was in effect a gang culture.

In other words, Mohammad Sidique Khan, the Mullah Crew and others like them had to find a new kind of Islam to which to relate, and Islamism filled the gap.

Rejecting the traditions and constraints of an older generation many of today's young Muslims shape their Islamist ideas not by attending sermons but by talking through ideas and attitudes with small groups or "gangs" of friends on the street and online.

A few years ago Newsweek magazine journalist, Sami Yousafzai, who himself survived an assassination attempt by extremists on the Pakistan - Afghanistan border wrote a piece entitled London's Armchair Taliban, while recuperating in the city. Among his many observations was that many young Muslims in Britain have a need to preserve a sense of identity though are themselves semi-immersed in Western culture and what was scary was the "amount of time they spend on jihadist websites".

Yousafzai pointed to the fact that "something of that far-off fight (Afghanistan), some tinge of blood and chaos and hatred, has certainly seeped into London's streets".

Afghanistan, Iraq, Somalia and Syria are all conflicts whose impact has percolated into sections of the Muslim communities in Europe.

In The Islamist, author Ed Husain tells of his journey as a 16-year-old towards becoming an Islamic extremist until five years later recanting and rejecting its tenets. During that process Husain tells of how it led to a battle with his pious but traditional father who eventually gave him an ultimatum: leave Islamism or leave my house. Husain decided to leave his house, going to an East London mosque, which was controlled by the Jamaat-influenced Islamic Forum. There he was taken in by "the brothers" and treated like a "family member".

For people like him, Husain says, "cut off from Britain, isolated from the Eastern culture of our parents, Islamism provided us with a purpose and place in life".

According to a "restricted" British intelligence MI5 report on radicalisation revealed a few years ago it is virtually impossible to draw up a typical profile of those who become involved in terrorism in Britain. Most, it concludes are "demographically unremarkable" and simply reflect the communities in which they live.

The extensive analysis carried out by MI5's behavioural science unit, based on hundreds of case studies, says there is no "single route to violent extremism".

For example, most are British nationals, not illegal immigrants and, far from being Islamist fundamentalists, most are religious novices.

Nor, the report concludes, are they "mad and bad". Many contributing factors are clearly at play here and youth subculture and street life are as significant as influences as are the hotbeds of extremism in some mosques or the sermons of fanatics.

As my journalist colleague Alex Massie, writing in Foreign Policy magazine, put it eloquently in a recent article: "For many, Islam is a vehicle for the cause more than it is necessarily - or, at least, initially - the cause itself."

Yesterday, Home Secretary Theresa May said she was preparing new laws and that Britain, "will be engaged in the struggle with British Islamist militants and jihadists for decades".

Foreign policy decisions, societal discrimination, and cultural alienation have all played their part in creating the current generation of homegrown jihadists. But so, too, have other less considered factors.

When in the early 90s American band Ice T released Cop Killer, there was talk of gangster rap being a threat to national security, a fear born out to some extent by the Los Angeles riots of 1992.

The real fear now in some quarters is that "jihadi-chic" has a similarly erosive subcultural pull on some young men in Western Europe.