The 40-year sentence imposed yesterday on Dhiren Barot, the Muslim convert who masterminded plans for mass murder on a horrendous scale, is one of the longest terms handed down for non-capital offences. It reflects not only the gravity of the appalling acts that this senior al-Qaeda operative was planning, his callous glee at the scale of death and injury and his cunning in elaborating plans to maim and terrify thousands of people in Britain and America; it is also a clear message to other fanatics abusing the name of Islam that a democracy will take whatever measures are needed to protect itself from such evil.

The threat posed by Barot is hard to envisage. The middle-class Hindu, who went to school in London and worked briefly as an airline ticket clerk, sought out the most radical and violent form of Islam after his conversion and spent the next nine years as a full-time terrorist planner. His expertise and professionalism in surveying the nine London hotels, three stations, synagogues, banks and Underground lines targeted for destruction is matched only by his sadism in contemplating how he could increase the panic and human suffering caused by exploding gas cylinders, napalm, nails and a radiation bomb.

It is vital, however, that the threat posed by such men is understood. Had it not been for a determined effort by this newspaper, together with the BBC and the Associated Press, no detail of what Barot was planning or of his sentence could have been made public. Confronted with overwhelming evidence, he pleaded guilty. But seven co-accused are currently on trial, and the courts had refused to lift any reporting restrictions for fear of prejudicing trials that may not end for two years.

Such gagging would have been utterly unacceptable. Ruthless, religiously inspired terrorism is the greatest danger this country faces. Britons were shaken from earlier complacency by the London suicide bombings in July last year. Many, though, still do not comprehend the aims or methods of those who would slaughter thousands to create “a black day for the enemies of Islam”. Simple vigilance is not enough. The security services mounted one of the largest operations undertaken to monitor and unravel his plot, but were up against a level of sophistication and terrorist training rarely seen until now. Their success in cracking encrypted messages, penetrating hidden computer data and identifying electronic keys and terrorist paraphernalia is remarkable.

None of this would have been known had the reporting restrictions not been lifted. This case has already led directly to the change in law allowing police to hold suspects for 28 days (but not the 90 days that the Prime Minister wanted) rather than 14 days, before charging them. It must surely now provoke a full debate on how terrorist cases are prepared, tried and reported. Dozens of suspects face trial on terrorism charges, and the virus has a long way to run before it is eradicated. British justice had yet to find ways of accommodating old and fair procedures to this challenge.

The Barot case underlines the character of terrorism, its international tentacles, chameleon adaptability and ability to exploit Western fads and weaknesses. It should, and will, make more urgent the need to penetrate and disarm the mindset that kills in the name of a deity. It is a threat that no democratic society can ignore.