I had a small warning that UCL was not the centre of enlightenment thinking it seemed when I went there to interview the urbane geneticist Steve Jones a couple of years ago. At the end of a discussion of the dangers of holding an unquestioning faith in the power of genetics to deliver miracle cures, he started to worry about creationism. I thought he would criticise the American religious Right, as all liberals were doing at the time. Instead, his urbanity cracked slightly and he began to talk about Islamist anti-Darwinism. When the publishers of a Turkish edition of Almost like a Whale — his updating of The Origin of the Species — flew him out to Istanbul, he was astonished when they told him that the Islamists saw evolutionary theory as a threat and then introduced him to his bodyguards. Back at the university in London, he heard more and more Muslim science students insisting that evolution could not be true.

"What do you say to them?"

"At the end of the course, I ask, ‘Was I lying to you about chromosome structure?' and they say no. Then I say, ‘Was I lying to you about cell structure?' and they say no. So I ask why on earth they think I'm lying to them about evolution, and of course they can't answer, because they're not allowed to'."

John Sutherland, a UCL English professor, remembers that at about the same time I was interviewing Jones, the Islamic Society was putting on a show of Islamic art. "A friend of mine strolled in to take a look. Was he a believer, asked an obviously Muslim student. No, replied my friend, he didn't believe in any God, as it happened. ‘Then,' the young man confidently informed him, ‘we shall have to execute you.' He wasn't joking; he was predicting. He wasn't going to draw a scimitar that minute and lop off the Godless one's head, but he implied that at some future point such things would happen. My friend laughed it off after lodging a mild complaint."

I do not believe I am reading too much into Sutherland's description when I guess that his friend's laughter was of the high and nervous variety. Nor is it unfair to say that a few academics knew that radical Islam was on campus long before Abdulmutallab attempted to kill himself and everyone flying with him. Once he had, any academic reading the story of how he went from Nigeria to Britain to Yemen to America should have noted and worried about the following details:

Abdulmutallab was not a tribune of the oppressed but yet another of radical Islam's poor little rich boys. The son of a Nigerian banker, he did not live in squalid student digs when he was at UCL, but in a West End apartment between the Wigmore Hall and Regent's Park. He was religious when he was in Nigeria, but his radicalisation began in supposedly secular London. His cousin recalled that after reaching Britain, "He changed. He was saying: ‘Islam, Islam, Islam'; he was saying we should all try to change and be more Islamic." He attended mosques that our tolerant intelligence services watch but do not close down. One intelligence source told the New York Times that he was "reaching out" to known extremists, but no one thought to bring him in for questioning.

As president of UCL Islamic Society, he organised an "anti-terror week", which featured a promotional video of clips of violence, accompanied by a soundtrack of hypnotic music. He inserted footage of George Galloway saying that the West believed that Palestinian blood was cheaper than Israeli blood and Amnesty International's poster boy Moazzam Begg alleging that the Americans tortured him at Guantanamo Bay. "When we sat down, they played a video that opened with shots of the twin towers after they'd been hit, then moved on to images of mujahedeen fighting, firing rockets in Afghanistan," one member of the audience said. "It was quite tense in the theatre, because I think lots of people were shocked by how extreme it was. It seemed to me like it was brainwashing, like they were trying to indoctrinate people."

Other guests at the society denounced gays, Jews, women, Christians, Hindus and Muslims who freely decided to change their mind about their religion. One regular invitee, Abu Usama adh Dhahabee, was caught on camera by Channel 4 crying: "We ask Allah to bring about the means and the ways in which the Muslims will get the power and the honour of repelling the oppression of the kuffar, where we can go out and perform the jihad. We ask Allah to bring that time so we can be participants in that. No one loves the kuffar. No one loves the kuffar. Whether these kuffar are from the UK, or from the US...We love the people of Islam and we hate the people of the kufr. We hate the kuffars. Whoever changes his religion from al-Islam to anything else, kill him in the Islamic state. Do you practise homosexuality with men? Take that homosexual man and throw him off the mountain."

Naturally, I wanted to hear the liberal administrators of a college inspired by the anti-clerical ideals of Jeremy Bentham explain why they allowed the death cults of the most anti-liberal ideology on the planet to flourish in their university. Unfortunately, the debate organised by UCL's admirably lively students began with a disappointment. Malcolm Grant, the university's provost, had stuck his head above the parapet a few days earlier to condemn the "quite disturbing Islamophobia" the case had raised, but then he ducked for cover and refused to attend.

In his place, he sent Philippe Sands, a law lecturer who is always accusing Tony Blair of being a war criminal for overthrowing the Ba'athist regime George Galloway saluted, but appears undisturbed by the production of actual criminals by his university. He didn't want to spy or snoop on his students, Sands said, and didn't see why any reasonable person should expect him to. His contemptuous tone and languid manner suggested that only modern McCarthyites could disagree. Following him was Wes Streeting, the Labour president of the National Union of Students, a young politician so stunningly slippery a seat in the Cabinet surely awaits him sometime in the late 2020s.

Streeting is gay as well as being left-wing. But he showed no concern about the presence of lethal homophobia and anti-Semitism among NUS members or about the pressures on Muslim students to conform to the dictates of Islamists. Instead of confronting an enemy in plain view, he thundered that the real foe of liberalism was Douglas Murray, the director of the Centre of Social Cohesion, who was speaking on the other side of the debate. Murray was a racist and an Islamophobe, he declared, without a care for the laws of libel or rules of honest debate. It was Murray who needed deradicalising, not student Islamic societies. He carried on in this vein even though virtually every Muslim who took to the podium agreed with Murray rather than him.

In theory, Streeting and Sands had a respectable argument at their disposal. Far from being racist monsters, Murray and his Muslim allies were, if anything, politically correct. They insisted in a rather wet manner that the university had a "duty of care" towards its students. Its own rules obliged administrators to protect the young from extremist preachers, and dangerous ideas. I listened uncomfortably. I have never believed in "no platform" for racist policies as long as liberals are at hand to confront racists and demonstrate to onlookers the malice of their arguments. John Stuart Mill, Jeremy Bentham's intellectual successor, opposed censorship but supported censuring. He wrote in his classic assertion of the need for free speech On Liberty:

"The peculiar evil of silencing the expression of an opinion is that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error."

A collision with the errors of messianic religion is, however, the last thing liberal Europeans want. At the underwear bomber's university, academics and student leaders alike were not prepared to argue with radical Islamists to give onlookers a livelier impression of the truth. They wanted to pretend that radical Islam did not exist and slink away from an urgent confrontation. As I watched Sands affect indifference and Streeting sneer and jeer, the thought that sprang to my mind was they were cowards, with a fear so deep they dare not admit it.

I can see no more important task at present than working out how European liberalism has gone so badly wrong. Why does a culture that prides itself on its opposition to bigotry become so feeble when it confronts bigots dressed in the black robes of clerical reaction? Until we understand, we cannot cure, and there is an emerging understanding among those who worry about the dark turn liberals have taken that Western guilt lies at the root of their moral failure.

After the Abdulmutallab case led the US to impose travel restriction on Nigeria, the Nigerian Nobel laureate Wole Soyinka said Britain should be the Americans' target. It was "a cesspit", he cried, the "breeding ground of fundamentalist Muslims". Nigerian national pride distorted his thinking. He could not seem to acknowledge that the religious war between Christians and Muslims in his own country was proceeding without British help. But one point he raised is being echoed by many others. Soyinka identified an inverse snobbery behind Britain's failure to argue against its enemies. Colonialism bred an innate arrogance, he said. But after the imperial adventure ended, arrogance produced a pride in openness so intense that it confirmed Britain's belief that it was still a morally great country.

Last month, Pascal Bruckner's magnificent The Tyranny of Guilt: An Essay on Western Masochism (Princeton) was published. Like the Nigerian novelist, the French philosopher sees an unacknowledged arrogance — "a blatant case of imperialism in reverse" — hiding behind the cries of Western liberals that we are the root cause of every psychopathic movement and regime on the planet.

"The whole paradox of sobered-up Europe is that it is no less arrogant than imperial Europe because it continues to project its categories on the rest of the world and childishly boasts that it is the origin of all the ills that beset mankind. Our superiority complex has taken refuge in the perpetual avowal of our sins, a strange way of inflating our puny selves to global dimensions."

Bruckner might have added that the consequences for Muslims are dire. Instead of meeting a confident liberalism in London, Abdulmutallab found a culture that insisted that the West offered a just cause for a war against itself; that declared he had every right to be furious, to despise liberal values as fraudulent and to believe in the moral superiority of radical reaction. Ayaan Hirsi Ali, whose contemptuous treatment by liberal European thinkers was one of the defining cultural events of the last decade, is equally clear that middle-class guilt explains why the dons of Oxford University wanted to shun her and employ Tariq Ramadan. When she arrived in Holland, fleeing the failed Muslim culture of Somalia, the extent of Europeans' scorn for the admirable civilisation they had built astonished her.

Her new Dutch friends said their country had exploited its colonies and failed to defend Holland's Jews from the Nazis. All true, but instead of producing a determination to do better, guilt led to indifference. When mass immigration began, liberals decided to celebrate difference rather than demand integration and allowed ghettoisation, sexual segregation and misogyny to flourish.

Ali, Bruckner and all those who agree with them are surely right, but they are missing a point which seemed obvious to me as I sat in UCL's debating chamber. White guilt doubtless explains the double standard that stops liberal England from seeing that the similarities between the BNP and the Muslim Brotherhood are more important that the differences.

But then take another look at the atheist teacher at UCL's Islamic Society art show. I suspect he was not overcome with remorse when the student announced that one day Islamists would kill him for his impiety, but shock and fear.

Or look at Philippe Sands. He seems a magnificent dissident when he accuses Tony Blair of being a war criminal, the more so when his friends and colleagues applaud his "bravery". Real bravery, however, involves the conscious acceptance of risk. Sands runs no risk in his public life. He can denounce Blair safe in the knowledge that the British state will not arrest him for defaming a former prime minister and that the provost of UCL will not sack him for sedition. If he had stood up at the debate on Abdulmutallab and announced that, of course, as a responsible academic he would seek to protect his students by spying on them, he would have run a risk, perhaps only a small risk, but a real one nevertheless. Suppose further that the papers picked up the story and reported that he had agreed to "snoop" on student Islamic societies, do you think his neighbours would have applauded his stand, or would they, like Ayaan Hirsi Ali's neighbours in Holland, mutter that it would be better if he moved house so as not to bring trouble into the area?

Or take the fulminating leader of the NUS. What would have happened to him if he had acknowledged that the police have now arrested four presidents of London student Islamic societies on terrorism charges, and it was time to tackle extremism on the campuses? Streeting knows full well that a brave stand would necessitate taking on the Muslim Brotherhood and Jammat-i-Islami and their far-Left allies — or should that be far-Right allies? — in the Socialist Workers Party. The result, as he must know, would be a huge campaign of denigration. His new opponents would accuse him of racism and Islamophobia in language which would be so extreme it could sound to some ears like an incitement to violence. Did he conclude that it was better to play it safe, and attack the enemies of extremism rather than the extremists themselves?

Ever since the Rushdie affair, the fear of religious violence has buzzed in the heads of liberal Europeans. The Islamists bombed London and Madrid, murdered Theo van Gogh, drove Ayaan Hirsi Ali into exile and forced politicians, most notably Muslim women politicians, to accept armed guards. On the scale of suffering in the world, Islamist violence in Europe is nothing remarkable. But a little fear goes a long way in rich and comfortable societies and sometimes the trouble with the liberals is not their guilt but that they do not begin to feel guilty enough about their cowardice and complicity.