The security services may not have been covered in glory by the official reports on the London bombings, but we must not ignore their insistence that intelligence alone will not protect us from terrorism. Contrary to speculation, the intelligence agencies are acutely aware of the need to attack the root causes of the new threat, for they of all people know that a strategy that depends primarily on observing and catching would-be bombers as they prepare their attacks is doomed to fail. So if we want to avoid a repetition of last summer's tragic events, the security services must make that case to ministers and persuade them to take the right actions.

To make a real difference we need a coherent strategy to prevent young British people being drawn into extremist violence in the first place. Yet despite pressure from across government - including from the intelligence agencies and the police - no such strategy yet exists.

The warning signs were there for long enough. The first British suicide bomber, Richard Reid, was thwarted (though only by his own incompetence) in 2001. Operation Kratos, the so-called shoot-to-kill policy, was introduced to counter suicide bombers in 2003, the year that two Britons set off to bomb Tel Aviv and a young Gloucester man planned to blow up a plane. Now most of the terrorist cases slowly finding their way to the courts involve British citizens.

The lesson of terrorism in Europe is that, once established, it takes a long time to eradicate. Isolated criminal groups such as Baader-Meinhof can be mopped up over a few years, but terrorism that renews itself from a deeper pool - from people who share something of the alienation and grievances that drive the extremists - lasts longer. Eta has just called a halt after 40 years. Who would believe the current convulsions with roots in the Muslim world will end any more quickly?

Despite the warnings before 2005, little serious action was taken in Britain. Yet a comprehensive strategy for tackling British extremism was presented to ministers in the spring of 2004. An analysis by Home Office and Foreign Office officials highlighted the causes drawing a minority of young Muslims towards extremists: anger at double standards in foreign policy; alienation of those trying to find a positive identity in a society that can be hostile to both race and faith; and the activism of young people who want to improve the position of Muslims at home and abroad. But this report was suppressed and even hidden from MPs on the home affairs select committee.

Judging by the past week, there is still no strategy. After the bombs, there was a flurry of engagement with the Muslim community, with Hazel Blears meeting selected leaders and working groups making recommendations. That momentum has been lost, the reports apparently forgotten. Cynicism at community level has deepened.

This is par for the course. Five years ago, the Cantle report on the riots in Bradford, Oldham and Burnley described communities living separate lives. Without the opportunities to develop shared values, suspicion, rejection and racism flourish. Yet few of the proposals to break down barriers were implemented. The problems are now more complex, with a greater number of young people aware of the alternative world-view offered by radical Islam. The Iraq war and other foreign policy issues have given a twist to the anger felt by those who identify with Muslim suffering.

Last week the government blamed bad theology. Extremist preaching certainly plays a role, but to hold sway it needs young people searching for its radical certainties. We can only reduce their numbers by addressing the complex mix of faith, cultural, generational, political and other factors shaping their concerns. Tackling the problem by suppressing the message will not work.

These are difficult issues, uncomfortable for the majority community as well as for parts of the Muslim one. Because it has failed to appreciate the roots of extremism, the government has lacked the will to drive through change. Responsibility has been scattered across departments with the focus further weakened by the reshuffle, which takes community issues out of the Home Office. Promising initiatives, such as the proposal to promote British values in schools, are made by junior ministers with little sign of backing from the top. No single minister is in charge of drawing together the strands of an effective community counter-terrorist strategy.

Most of the Muslims consulted last summer wanted a public inquiry, not to find someone to blame but to bring the difficult roots of extremism into the open and to prompt a response from both the government and their own community. That demand should not go away.

John Denham chairs the Commons home affairs select committee and was minister of state at the Home Office, 2001-2003

Martin Bright is away