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.