The number was revealed to The Independent by Sir Norman Bettison, the chief constable of West Yorkshire Police and Britain's most senior officer in charge of terror prevention.
He said the "Channel project" had intervened in the cases of at least 200 children who were thought to be at risk of extremism, since it began 18 months ago. The number has leapt from 10 children identified by June 2008.
The programme, run by the Association of Chief Police Officers, asks teachers, parents and other community figures to be vigilant for signs that may indicate an attraction to extreme views or susceptibility to being "groomed" by radicalisers. Sir Norman, whose force covers the area in which all four 7 July 2005 bombers grew up, said: "What will often manifest itself is what might be regarded as racism and the adoption of bad attitudes towards 'the West'.
"One of the four bombers of 7 July was, on the face of it, a model student. He had never been in trouble with the police, was the son of a well-established family and was employed and integrated into society.
"But when we went back to his teachers they remarked on the things he used to write. In his exercise books he had written comments praising al-Qa'ida. That was not seen at the time as being substantive. Now we would hope that teachers might intervene, speak to the child's family or perhaps the local imam who could then speak to the young man."
The Channel project was originally piloted in Lancashire and the Metropolitan Police borough of Lambeth in 2007, but in February last year it was extended to West Yorkshire, the Midlands, Bedfordshire and South Wales. Due to its success there are now plans to roll it out to the rest of London, Thames Valley, South Yorkshire, Greater Manchester, Leicestershire, Nottinghamshire, and West Sussex.
The scheme, funded by the Home Office, involves officers working alongside Muslim communities to identify impressionable children who are at risk of radicalisation or who have shown an interest in extremist material – on the internet or in books.
Once identified the children are subject to a "programme of intervention tailored to the needs of the individual". Sir Norman said this could involve discussions with family, outreach workers or the local imam, but he added that "a handful have had intervention directly by the police".
He stressed that the system was not being used to target the Muslim community. "The whole ethos is to build a relationship, on the basis of trust and confidence, with those communities," said Sir Norman.
"With the help of these communities we can identify the kids who are vulnerable to the message and influenced by the message. The challenge is to intervene and offer guidance, not necessarily to prosecute them, but to address their grievance, their growing sense of hate and potential to do something violent in the name of some misinterpretation of a faith.
"We are targeting criminals and would-be terrorists who happen to be cloaking themselves in Islamic rhetoric. That is not the same as targeting the Muslim community."
Nor was it criminalising children, he added. "The analogy I use is that it is similar to our well-established drugs intervention programmes. Teachers in schools are trained to identify pupils who might be experimenting with drugs, take them to one side and talk to them. That does not automatically mean that these kids are going to become crack cocaine or heroin addicts. The same is true around this issue."
But Inayat Bunglawala of the Muslim Council of Britain said the police ran the risk of infringing on children's privacy. He warned: "There is a difference between the police being concerned or believing a person may be at risk of recruitment and a person actually engaging in unlawful, terrorist activity.
"That said, clearly in recent years some people have been lured by terrorist propaganda emanating from al-Qa'ida-inspired groups. It would seem that a number of Muslim youngsters have been seduced by that narrative and all of us, including the Government, have a role to play in making sure that narrative is seen for what it is: a nihilistic one which offers no hope, only death and destruction."
A Home Office spokesman said: "We are committed to stopping people becoming or supporting terrorists or violent extremists. The aim of the Channel project is to directly support vulnerable people by providing supportive interventions when families, communities and networks raise concerns about their behaviour."
