The raids on houses in Leeds yesterday and subsequent police indications that the London atrocities were probably carried out by four suicide bombers born and raised in Britain are disturbing. The police deserve credit for a swift reaction, but there is no doubt that the consequences of their discovery will be long-lasting.

Those who have had to wait an agonisingly long time for formal identification of loved ones believed to have been killed in the attacks can draw some slight comfort from the news. The detailed analysis and painstaking DNA matching of the victims have led police to locations in Leeds and Luton. It is to be hoped that these breakthroughs will enable police to provide details as quickly as possible to the families of the innocent victims.

The conclusion that the terrorists were home-grown is deeply unsettling. It does not, in any way, close this case. Urgent questions follow. Who proposed and co-ordinated this plot? What links did the bombers have to al-Qaeda and related terrorist organisations overseas? How did the bombers obtain their materials? And how were they able to keep their deadly plans secret, without arousing suspicion among their families, neighbours or fellow Muslims?

Answers to the first two must now await the huge international collaborative effort under way to pool and hone intelligence on fundamentalist terrorism. As part of that effort, today’s meeting of European interior and justice ministers should give approval to Britain’s request for a clampdown on terrorist financing and access to mobile telephone and e-mail records for up to a year. As for the access to deadly materials, there should be an urgent review of the security of explosives and bomb-making equipment, both military and improvised, and tighter regulation of all substances that can be used for bomb-making.

It is the fourth question that raises the toughest issues. Is it really possible that no one beyond the bombers had any inkling of their intentions? Were their extremist views and plans unknown even in the circle of friends and fellow Muslims who may have shared their fanaticism and hostility to the society in which they grew up? A tremendous burden of responsibility now rests on the Muslim community. Its leaders, educated and articulate, have repeatedly spoken out and condemned extremism. But it is at local level that action needs to be taken. Tolerance of extremism is utterly unacceptable.

It is not some harmless view of hotheaded youth; it is an insidious cult that feeds on fanaticism, intolerance and the mindlessly macho posing of would-be rebels hoping to win glory. It leads directly to tragedy, as the bombs in London, Madrid, Bali, Istanbul and elsewhere have shown.

Too often such views have not only been tolerated but actually disseminated in mosques by ill-educated imams, brought over from villages in Pakistan, unable to speak English and ill-equipped to guide young Muslims in a Western society. Adrift in their job, they have resorted to preaching the crudest form of jihad. This may influence only a tiny minority, but that minority is capable of wreaking havoc within the Muslim community and between communities. The law-abiding majority must recognise a responsibility to end the cult of nihilistic extremism and an imperative to be intolerant of intolerance.