A network of “extremist recruiters” is circulating on campuses targeting people with “technical and professional qualifications”, particularly engineering and IT degrees.

Yesterday it emerged that last week’s London bombings were a sophisticated attack with all the devices detonating on the Underground within 50 seconds of each other. The police believe those behind the outrage may be home-grown British terrorists with no criminal backgrounds and possessing technical expertise.

A joint Home Office and Foreign Office dossier — Young Muslims and Extremism — prepared for the prime minister last year, said Britain might now be harbouring thousands of Al-Qaeda sympathisers.

Lord Stevens, the former Metropolitan police chief, revealed separately last night that up to 3,000 British-born or British-based people had passed through Osama Bin Laden’s training camps.

The Whitehall dossier, ordered by Tony Blair following last year’s train bombings in Madrid, says: “Extremists are known to target schools and colleges where young people may be very inquisitive but less challenging and more susceptible to extremist reasoning/ arguments.”

The confidential assessment, covering more than 100 pages of letters, papers and other documents, forms the basis of the government’s counter-terrorism strategy, codenamed Operation Contest.

It paints a chilling picture of the scale of the task in tackling terrorism. Drawing on information from MI5, it concludes: “Intelligence indicates that the number of British Muslims actively engaged in terrorist activity, whether at home or abroad or supporting such activity, is extremely small and estimated at less than 1%.”

This equates to fewer than 16,000 potential terrorists and supporters out of a Muslim population of almost 1.6m.

The dossier also estimates that 10,000 have attended extremist conferences. The security services believe that the number who are prepared to commit terrorist attacks may run into hundreds.

Most of the Al-Qaeda recruits tend to be loners “attracted to university clubs based on ethnicity or religion” because of “disillusionment with their current existence”. British-based terrorists are made up of different ethnic groups, according to the documents.

“They range from foreign nationals now naturalised and resident in the UK, arriving mainly from north Africa and the Middle East, to second and third generation British citizens whose forebears mainly originate from Pakistan or Kashmir.

“In addition . . . a significant number come from liberal, non-religious Muslim backgrounds or (are) only converted to Islam in adulthood. These converts include white British nationals and those of West Indian extraction.”

The Iraq war is identified by the dossier as a key cause of young Britons turning to terrorism. The analysis says: “It seems that a particularly strong cause of disillusionment among Muslims, including young Muslims, is a perceived ‘double standard’ in the foreign policy of western governments, in particular Britain and the US.

“The perception is that passive ‘oppression’, as demonstrated in British foreign policy, eg non-action on Kashmir and Chechnya, has given way to ‘active oppression’. The war on terror, and in Iraq and Afghanistan, are all seen by a section of British Muslims as having been acts against Islam.”

In an interview yesterday, Blair denied that the London terrorist attacks were a direct result of British involvement in the Iraq war. He said Russia had suffered terrorism with the Beslan school massacre despite its opposition to the war, and terrorists were planning further attacks on Spain even after the pro-war government was voted out.

“September 11 happened before Iraq, before Afghanistan, before any of these issues and that was the worst terrorist atrocity of all,” he said.

However, the analysis prepared for Blair identified Iraq as a “recruiting sergeant” for extremism.

The Sunday Times has learnt that Britain is negotiating with Australia to hand over military command of southern Iraq to release British troops for redeployment in Afghanistan.

The plan behind Operation Contest has been to win over Muslim “hearts and minds” with policy initiatives including anti-religious discrimination laws. A meeting of Contest officials this week is expected to consider a radical overhaul of the strategy following the London attacks.

Stevens said last night at least eight attacks aimed at civilian targets on the British mainland had been foiled in the past five years and that none had been planned by the same gang.

The former Scotland Yard chief, who retired earlier this year, said that on one weekend more than 1,000 undercover officers had been deployed, monitoring a group of suspected terrorists.

He said that he believed last week’s attackers were almost certainly British-born, “brought up here and totally aware of British life and values”.

“There’s a sufficient number of people in this country willing to be Islamic terrorists that they don’t have to be drafted in from abroad,” he said.

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