It's that time of the year again. And alongside the familiar traditions of carols, tinsel and unwanted gifts, comes a new tradition: Somewhere in the world a Muslim radicalized in Britain will try to blow up innocent men, women and children in a suicide mission.

That appears to have been the case of Taimur Abdulwahab al-Abdaly. Authorities believe the Iraqi-born Swede gained his extremist views while at university in Luton, England, before he headed to Stockholm and allegedly detonated the bombs that killed himself and injured two Christmas shoppers last Saturday. Sound familiar?

On Dec. 22, 2001, a British man named Richard Reid tried to bring down a commercial flight from Paris to Miami with bombs placed in his shoes. On Christmas Day the year before, a British man of Pakistani origin, Bilal Ahmed, is believed to have rung in the festive season by killing himself and several others in Kashmir with a bomb. And last year, while most British families were eating their turkey, Omar Farouk Abdulmutallab, formerly of University College London, allegedly tried to blow up a plane over Detroit with an explosive device concealed in his underpants.

For those who have warned for years about the radicalization of Britain's young Muslims, this is becoming repetitive and depressing. In 2007, my think tank, the Center for Social Cohesion, commissioned an investigation into Muslim students' activities and opinions. We monitored a range of British universities and found a scene notable for its Islamist hate-preachers, highly divisive literature, and discussion groups in which religious worship is hijacked by radical politicking.

Our poll found that almost one-third of British Muslim students believed that killing in the name of their religion could be justified. At the time the government's minister for higher education dismissed the findings, as did the National Union of Students. 

This year we published a comprehensive list of the extremist speakers who appear, unchallenged, every week at British universities. These speakers have advocated suicide bombings, the murder of soldiers and innocent civilians, and the persecution of religious and sexual minorities in Britain.

One such speaker was Anwar al-Awlaki, now the subject of a "kill or capture" order from President Barack Obama. Awlaki was until last year an invited favorite at British universities' Islamic Societies.

Last month Roshana Choudhry, previously a student at Kings College London, was convicted of attempted murder after stabbing Stephen Timms, a Labour parliamentarian who voted for the war in Iraq. She told police she had been inspired by Islamic scripture and Internet videos of Awlaki's sermons.

And still it goes on. Just last week, across the road from Kings College, the Palestine Society at the London School of Economics (LSE) hosted Abdel Bari Atwan, a man with a long record of extreme statements. Three years ago he said that "If the Iranian missiles strike Israel—by Allah, I will go to Trafalgar Square and dance with delight."

He reportedly used his platform at LSE last week to tell Jewish students that they had "bombed Gaza" and to warn of the "Jewish lobby." His audience could also look to the example of Omar Sheikh, the illustrious LSE graduate who in 2002 was involved in the murder of Daniel Pearl, a reporter for this newspaper.

You might have thought that these and other incidents, repeated time and again, would wake up the British authorities. But they do not. When the University College of London, where Abdulmutallab was president of the Islamic Society, faced criticism after last year's botched Christmas Day bombing, it commissioned an investigation. The inquiry found "no evidence to suggest either that Umar Farouk Abdulmutallab was radicalized while a student at UCL or that conditions at UCL during that time or subsequently are conducive to the radicalization of students."

The friends and family of the suspected Swedish bomber certainly seem to blame Britain and its institutions. A former friend of Abdaly tells London's Telegraph: "He didn't care about politics or religion. . . . But then he went to England to study in 2001 and everything changed. When he came back he had grown a beard and he was very serious. He talked about Afghanistan and religion and did not want to hang out with his friends."

It's a story that is becoming as familiar as the traditional nativity: Ordinary young man goes to Britain, most likely to study, and comes out an Islamic extremist. If you had told Britons 20 years ago that this sort of thing was going to become routine in the 21st century, they would have laughed at you. But Britain is no longer the country it was.

Mr. Murray is the director of London's Center for Social Cohesion.