IN THE FIRST FEW DAYS after the horror in London on July 7, media in Britain and abroad focused considerable attention on "Londonistan"--the local zoo of Islamist agitators, almost entirely Arab, who have made headlines for years with their extremist preaching. Analytical lines, many of them useful, were drawn to al Qaeda and Iraq, but almost nobody looked at domestic Muslim extremism in the United Kingdom. Close observers of the British Islamic community, however, few of whom seem to have been consulted by reporters or the government, had been discussing for months a dramatic increase in radical agitation by Pakistani...