None of the four young men from West Yorkshire who killed 52 bus and Tube passengers during the summer fitted the existing “threat profile”.

Senior police officers involved in planning future anti-terrorist strategy are struggling to draw up a new topology of what makes a young British Muslim want to become a martyr for the jihad.

The Times has obtained some of the material being prepared at Scotland Yard to gauge the terrorist threat. At first glance the bewildering colour-coded diagrams, lists and flow charts appear to be part of some academic endeavour. There are arrows, dotted lines and boxes labelled with impenetrable phrases and jargon.

However, these are the physical representations of what is going on inside the minds of the police officers charged with trying to prevent a repeat of 7/7. They are very much a work in progress. In the absence of any reliable stereotype of a terrorist, this is an attempt to identify the influences that brainwash young men and lead them to the point where they blow themselves and dozens of innocent people to bits.

The radicalisation of a potential recruit begins, typically, with an extremist preacher who dispatches “talent scouts” to find young Muslims who might be willing to answer the call. Some of these hardline clerics are well known. But their scouts, disciples and other less prominent preachers are often unknowns. Unobtrusively, they set to work on their target recruits. The first meeting place might be a mosque, but the radicals have also set their sights on universities and prisons.

A former militant leader in Iraq who has fought alongside young Britons in attacks against British troops said that UK mosques were now controlled by “moderates” and were no longer recruiting grounds.

The ex-commander, who calls himself Abu Ahmad, claimed that most of the Britons sent to Iraq were “talent spotted” in gymnasiums and Islamic bookshops, as well as at pubs and discos.

The young target may well be a vulnerable personality, exhibiting a sense of injustice and alienation or a need to belong.

The recruiter will use apparently chance meetings to chat, gradually drawing him into Islamist circles. There will be study groups, private prayer meetings and viewings of propaganda from Iraq, Chechnya and other jihadi battlefields.

It is, one senior Scotland Yard source says, a process of “ideological grooming”, not unlike the techniques used by paedophiles to coach and coax their victims.

Mohammad Sidique Khan, the oldest of the 7/7 bombers and apparent leader of the cell, used these methods. Using youth centres, gyms, whitewater rafting trips and jihadi videos, he convinced Jermaine Lindsay, Shehzad Tanweer and Hasib Hussain of the need to murder innocent people to defend their religion.

Analysts of Islamist terrorism have identified the 7/7 bombers as forerunners of the next al-Qaeda generation. Michael Scheuer, of the Jamestown Foundation, said: “The UK-born and raised suicide bombers of 7/7 foreshadow the next mujahidin generation who will operate below the radar of local security services.”

Khan had come to the attention of the intelligence services as an associate of other men who were suspected of involvement in a terrorist bomb plot. But he was not pursued because he did not tick enough of the boxes in the pre-July profile of the terror suspect.

A crucial part of the July jigsaw, and one that is still missing, is discovering how Khan, a teaching assistant and father of young children, was radicalised. He visited Pakistan, with Tanweer, and is thought to have spent time at training camps run by groups linked to al-Qaeda.

But Khan’s mentor, the possible mastermind of the 7/7 attack, has not been identified and the possibility remains that Khan was a self-taught bomber, learning his craft from sophisticated internet sites that carry bombmaking manuals alongside religious instructions.

A senior police source said: “It would be quite a revelation if this group had no one running it at all. If that is so we really are in a mess.”

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