After the bombings, and their grim echo in yesterday’s terrorist attack in Turkey, the search for explanations. The news that the London bombers were home-grown will have come as no surprise to anybody who read this newspaper last week, although some sought comfort in the idea that a shadowy foreign terrorist cell was responsible. The banal ordinariness of the bombers’ lives fits the pattern of previous outrages. It could hardly be any other way; people who lead full and interesting lives do not commit such actions. Unfulfilled losers do.

The search for explanations takes us into familiar territory. Many of Britain’s 1.6m Muslims, it is argued, are alienated. Unemployment is 14% among Muslim men and 22% among 16 to 24- year-olds. One in three Muslims has no qualifications. Many Muslims, we are told, are offended by the godless state of Britain, the casual thuggery and antisocial behaviour on our streets, the lack of respect, the binge drinking and the air of moral decline. But hang on. Many people, young and old and whatever their ethnic or religious background, have been subject to economic disadvantage and the tedium and despair of unemployment. The overwhelming majority of the population is offended by the behaviour of the antisocial minority and frustrated by the government’s failure to follow through on its “respect” agenda.

What about Iraq? Clare Short, the former international development secretary, will say in a pre-recorded GMTV interview today that she has “no doubt” the Iraq invasion was a factor in the London bombings. In this, she is echoing George Galloway. British Muslims, having seen their brothers die in Iraq in what they see as an illegal war, have been inflamed into revenge. Yesterday’s killing of three British soldiers in Amarah shows how far from peace Iraq remains. But the idea that the bombings were a direct response to the war is untestable and merely gives terrorists an excuse on which to hang their atrocities.

Late in 2002 the Muslim Council of Britain warned the Muslim community against “agents provocateurs” who would seek to exploit anti-war feelings. On this the council, like the government, was ineffectual. The families of the four bombers cannot understand how they came to have murderers in their midst. According to the family of Mohammad Sidique Khan, the 30-year-old former teaching assistant responsible for one of the bombs, he must have “been brainwashed into carrying out such an atrocity”.

If so, we know who the brainwashers were. We should look to Hizb ut-Tahrir, a militant Islamic youth organisation which is banned in Germany and Holland but is free to spread its message outside British mosques. Or to Al-Muhajiroun, an Islamist group that condones violence. Or to Dr Azzam Tamimi, a spokesman for the Muslim Association of Britain and director of the Institute of Islamic Political Thought, who was given a platform on the BBC’s Newsnight last week and who declared last year that he would be prepared to carry out a suicide bombing in Israel.

Stable doors are being belatedly closed. On Friday a group of leading British Muslim scholars issued a statement saying that the London atrocities “have absolutely no sanction in Islam” and that the bombers were “criminals not martyrs”. Charles Clarke, the home secretary, plans a new offence of indirect incitement of terrorism to “capture the expression of sentiments which do not amount to direct incitement to perpetrate acts of violence, but which are uttered with the intent that they should encourage others to commit, or attempt to commit, terrorist acts”.

We cannot know whether the bombers were driven by the incitement of others. What we do know is that Britain has for too long been tolerant of the messengers of hate, many of whom have been foolishly admitted from abroad. Action will now be taken. It is a pity that it took the deaths of more than 50 innocents to bring it about.