The mills closed in the 1980s. The general depression of the mill-and-mosque towns that resulted was reflected in rundown, restless schools, without ambition or excellence. The ambulance-chasers of the left called for more multiculturalism in these schools, which gave cover to the ex-peasant community's demands for Islamization. They demanded that girls and boys be taught separately, that girls cover their heads and limbs, that schools serve halal meat, that Arabic and the Koran be taught, that history classes depict Britain primarily as an exploitative nation. Principals who resisted were branded racists.

On college campuses, some students began to dress in an Islamic way. They reformed their speech and friendships. They began to characterize the gains of feminism as immorality. Their puritan disgust for the West's popular culture and sexual license, their support for laws that decree the stoning to death of adulteresses, became the profession of an allegiance alienated from the Britain that allows them the freedom to express these views.

These new zealots had been brought up in a traditional way by parents whose religious views were generally orthodox but not extremist. But in the 1980s, a new Muslim leadership of mullahs, financed by various Islamic powers around the world, was setting up mosques and schools in Britain, thanks to an immigration-law loophole that allows clergymen open-ended permission to stay. Muslim adolescents attracted to this radical preaching came under the domination of the new mullahs, who offered a luminously simple explanation of the cosmos and promised membership in an organization that would dominate the world. "We carry Islam as a political belief, a complete system," says Muhammad Omar Bakri, a poisonous cleric who runs a London Muslim organization. "We don't carry Islam as a religion. It's an ideology."

All this came to light in the most significant divide in Britain's multicultural history: the Rushdie affair, which uncovered a fifth column whose literary criticism entailed book burning and death threats. The British Muslim community echoed the call of Ayatollah Khomeini to kill the writer. There were denunciations of Salman Rushdie in every mosque. Not one mullah--not one--raised a voice in support of freedom of creativity; no mullah ventured the opinion that the fatwa was wrong. Though the supposedly liberal Muslim commentators whom the British press retains were not in favor of the death sentence, none would extend himself to defend the book. One ugly book burning was led by a Muslim who was forced to admit that Iran had financed him.

Before the fatwa, the politically correct position was that, with a few concessions, and with some welcome additions to British cuisine, the new immigrant communities would be assimilated into British life with hiccups but not convulsions. The fatwa affair--when the entire Islamic community united behind the condemnation--should have put an end to the idea. After all, if you prostrate yourself to an all-powerful being five times a day, if you are constantly told that you live in the world of Satan, if those around you are impervious to literature, art, historical debate and the values of Western civilization, your mind becomes susceptible to fanaticism. Your mind rots. Worse, it can become the instrument of others who send you on suicidal missions.

The incident should have alerted Britain to the rise of a phenomenon that couldn't be explained by theories of race relations. It didn't. Liberal opinion, while not admitting that the Yemeni Six were out to kill Britons, called for an examination of the racism that had alienated them.

Then, this summer, riots broke out in several mill-and-mosque towns. A few hundred masked "Asian" (which in Britain refers to Indians, Pakistanis and Bangladeshis) youths torched shops and cars. They fought the police with staves and stones. The pundits and officials in charge of race relations were bewildered. They attributed these riots to the "failure of years of race relations," to resentment of poverty and unemployment, and to rumors that neo-fascist anti-immigrant organizations were invading these towns.

What they failed to mention was that the rioters weren't "Asian" but Muslim. The difficulties Muslim culture places in the way of assimilation have produced a generation of disaffected youth, highly susceptible to the incitements of militants.

After Sept. 11, Mr. Hamza was wheeled out, together with Mr. Bakri, who had been expelled from his native Syria and is funded by Saudi money. They both said that they supported the jihad, that the laws of men did not matter, and that only the Koran, as interpreted by them, of course, could govern the thinking of the Muslim. Upscale Muslim organizations expressed regret at the atrocity and denounced Messrs. Hamza and Bakri.

Yet outside Britain's mosques, young men of jihadi persuasion bellowed slogans supporting the terrorist attack, exhorting worshipers to "join the war" against America. A poll by the Sunday Times found that 40% of British Muslims think Osama bin Laden is "justified" in his war and that the British citizens who joined the Taliban were right to do so. One can't shelter in one's home those who would kill you. Yet Britain has given permission to stay to the likes of Messrs. Hamza and Bakri. The very liberalism against which they preach has nursed this Fifth Column.

What Islam needs is a reformation, and if this very concept is forbidden in the unchangeable word of the Koran, there is enough Islamic history to support a reforming interpretation of the law of living with others. The Muslims in Britain and the U.S. who are educated in Western disciplines and culture must spark this reformation. As for the officials of the U.S. and Britain, they need to redirect the energy that they have poured into race relations and multiculturalism into a defense of the values of freedom and democracy. Their future depends on it.