Can you guess which books the wannabe jihadists Yusuf Sarwar and Mohammed Ahmed ordered online from Amazon before they set out from Birmingham to fight in Syria last May? A copy of Milestones by the Egyptian Islamist Sayyid Qutb? No. How about Messages to the World: the Statements of Osama Bin Laden? Guess again. Wait, The Anarchist Cookbook, right? Wrong.

Sarwar and Ahmed, both of whom pleaded guilty to terrorism offences last month, purchased Islam for Dummies and The Koran for Dummies. You could not ask for better evidence to bolster the argument that the 1,400-year-old Islamic faith has little to do with the modern jihadist movement. The swivel-eyed young men who take sadistic pleasure in bombings and beheadings may try to justify their violence with recourse to religious rhetoric – think the killers of Lee Rigby screaming “Allahu Akbar” at their trial; think of Islamic State beheading the photojournalist James Foley as part of its “holy war” – but religious fervour isn’t what motivates most of them.

In 2008, a classified briefing note on radicalisation, prepared by MI5’s behavioural science unit, was leaked to the Guardian. It revealed that, “far from being religious zealots, a large number of those involved in terrorism do not practise their faith regularly. Many lack religious literacy and could . . . be regarded as religious novices.” The analysts concluded that “a well-established religious identity actually protects against violent radicalisation”, the newspaper said.

For more evidence, read the books of the forensic psychiatrist and former CIA officer Marc Sageman; the political scientist Robert Pape; the international relations scholar Rik Coolsaet; the Islamism expert Olivier Roy; the anthropologist Scott Atran. They have all studied the lives and backgrounds of hundreds of gun-toting, bomb-throwing jihadists and they all agree that Islam isn’t to blame for the behaviour of such men (and, yes, they usually are men).

Instead they point to other drivers of radicalisation: moral outrage, disaffection, peer pressure, the search for a new identity, for a sense of belonging and purpose. As Atran pointed out in testimony to the US Senate in March 2010: “. . . what inspires the most lethal terrorists in the world today is not so much the Quran or religious teachings as a thrilling cause and call to action that promises glory and esteem in the eyes of friends, and through friends, eternal respect and remembrance in the wider world”. He described wannabe jihadists as “bored, under­employed, overqualified and underwhelmed” young men for whom “jihad is an egalitarian, equal-opportunity employer . . . thrilling, glorious and cool”.