Far in the distance, a protracted scream comes out of a dark tunnel. As it rises, the ground begins to shake. A dot of light speeds towards the viewer. In seconds, it fills the screen and a rattling blur of the cold steel shrieks past the camera.

The action cuts to the forecourt of King's Cross station. Hasib Hussein, a gawky 18-year-old with soft eyes, looks imploringly at the authoritative figure of Sidique Khan.

"Sidique ... wait ... ," he says, with a voice full of fear and uncertainty. The older man calms the boy with a bear hug.

"There is nothing to fear in death, Hasib," he says. "When the time comes, we'll face towards Makkah together, as one." He looks Hussein in the eyes. "Our lives begin today."

Hussein nods. Khan ruffles his hair, and disappears to slaughter commuters on the London Underground. Hussein screws up his courage and prepares to murder an equally random collection of passengers on a bus heading out from King's Cross.

So begins The London Bombers, one of the most thoroughly researched and politically important drama-documentaries commissioned by British television. A team of journalists, at least one of whom was a British Muslim, reported to Terry Cafolla, a fine writer who won many awards for his dramatisation of the religious hatred which engulfed the Holy Cross school in Belfast.

The reporters spent months in Beeston, the Leeds slum where three of the four 7/7 bombers - Sidique Khan, Hasib Hussein and Shehzad Tanweer - grew up. Unusually for journalists working within BBC groupthink, they didn't find that the "root cause" of murderous rage was justifiable anger at the "humiliation" America, Israel, Britain and Denmark and her tactless cartoonists had inflicted on Muslims.

Instead, they inadvertently confirmed the ideas of Ernest Gellner, the late and unjustly neglected professor of anthropology at Cambridge. In Postmodernism, Reason and Religion (1992), Gellner asked why a puritanical version of Islam was in the ascendant when godlessness was flourishing everywhere else. His answer was that Wahhabism and its ever more zealous theocratic variants could appear as modern as secular humanism. They represented the pure religion of scholars and the city, which would free Muslims from their peasant parents' embarrassingly superstitious faith. Accepting fanaticism was a mark of superiority: a visible sign of upward mobility from rural idiocy to urban sophistication.

And so it proved in Leeds. The picture of Beeston the BBC presents is a disorientating mixture of the parochial and the cosmopolitan. On one hand, Beeston is almost as much of a village as the ancestral homes of its Pakistani inhabitants. On the other, its parochialism is an illusion. Cheap flights take the bombers to the madrassas and terrorist training camps of Pakistan. The internet connects them to the global jihadi network.

In one telling scene, Hasib Hussein hears a message ping on his mobile. He flips it open and finds a beheading video. He watches the snuff movie impassively, showing no emotion when the killer cuts a hostage's throat. Later Khan and Hussein learn how to make a bomb, not by infiltrating an army regiment, but by the simple expedient of going to an internet café and logging on to an Arab jihadi site. "What did people do before Google?" the admiring Hussein asks.

Sidique Khan is the dominant figure. He turns against the traditional Sufism of his father, who remains stuck in the tribal and religious loyalties of the subcontinent. By breaking with both, Khan escapes an arranged marriage designed to keep wealth within the extended family, and enters into a love match with a fellow student at Leeds Metropolitan University.

His father's pir, or Sufi priest, demands a hearing. While Khan waits to talk to him, he sees the elder hang a miracle cure - a miniature Koran - round a child's neck. Khan looks on in disgust. "What you do here is not harmless, it's dangerous," he thunders. "How dare you contaminate Islam? There is only one Allah and he does not share his power, not with anyone... Your tradition of Islam, your parlour tricks, they belong in the hills of Pakistan."

The London Bombers works so well because it is a family drama about inter-generational conflict as well as an account of the largest British massacre since Lockerbie. The BBC captures the claustrophobic milieu of bodybuilding and vigilantism into which the men retreat. The bomb-making in a tiny terraced house becomes a male-bonding ritual in which the members of a cult of death squash each other's doubts.

"How can we keep Muslims off the Tube that day?" asks Abdullah Jamal,
the fourth bomber. "They'll go straight to paradise," answers Sidique. "It is quadaa [fate] that they're there. And if it is Allah's wish ..." (Pause ). "We need more acetone."

So psychologically convincing is the portrayal of macho loyalty and lure of barbarism that viewers can understand how these men turn into mass murderers.

Except that they can't and won't understand, because the BBC will not give them the opportunity to understand. This is a review of a drama that was never made.

The reporters convinced the families of three of the four bombers to cooperate. By the end, they agreed that the BBC's account of their sons and brothers' lives and deaths was accurate. Cafolla submitted five versions of the script. He was working up to a final draft when the BBC abandoned the project.

The official reason is that the drama didn't make the grade. The script is circulating in Samizdat form, which is how it reached Standpoint, and every writer and director who has read it disagrees. The journalists, however, say that BBC managers told them they were stopping because it was "Islamophobic".

Eh? The defining characteristic of Islamophobic prejudice is the belief that all Muslims are potential terrorists, and yet here, apparently, is the BBC seconding that motion by arguing that a dramatic examination of terrorism would be offensive to all Muslims.

It makes no sense until you understand the moral contortions of the postmodern liberal establishment. In the past few years, the Foreign Office, the Home Office, the West Midlands Police, the liberal press, the Liberal Democrats, the Metropolitan Police, the Crown Prosecution Service, the Lord Chief Justice and the Archbishop of Canterbury have all either supported ultra-reactionary doctrines or made libellous accusations against the critics of radical Islam. All have sought to prove their liberal tolerance by supporting the most illiberal and intolerant wing of British Islam, and by blocking out the voices of its Muslim and non-Muslim critics as they do it.

As the sorry history of The London Bombers shows, they have left us a country that cannot tell its own stories; a land so debilitated by anxiety and stupefied by relativism that it dare not meet the eyes of the face that stares back at it from the mirror.