Dhiren Barot, 34, a Hindu convert to Islam, admitted planning terrorist bomb outrages that could have caused “carnage, bloodshed and butchery” on both sides of the Atlantic.

Passing sentence at Woolwich Crown Court, Mr Justice Butterfield told Barot that he was a “determined and dedicated terrorist, a highly intelligent and very dangerous man”.

The judge said that Barot had begun his “intensive training in the black arts of terrorism” in 1995. He said: “You have devoted most of your adult life to seeking means to bring death and destruction to the Western world. For reasons which I do not begin to understand you decided that you should use the life that you have been given in order to end the lives of others.”

Barot, the judge continued, would pose a threat to the public for many years: “I cannot know if it would ever be safe to release you.”

Barot stared impassively at the judge as he spoke. Then, on hearing the 40-year tariff, he gathered up his papers and walked from the dock, casting an angry backward glance at the Bench.

His conviction and long sentence are regarded as a legal landmark by agencies engaged in the fight against Islamist terrorism.

Barot, a Briton from a middle-class background, became one of Osama bin Laden’s most experienced and elusive operatives. He embraced holy war against the West long before 9/11 or the invasions of Afghanistan or Iraq, writing a book in 1999 in which he advocated “worldwide jihad” to bring nations “to their knees”.

“Terror works,” he told his readers. “That is why the believers are commanded to enforce it by Allah.” The book, The Army of Madinah in Kashmir by Esa al-Hindi, is still on sale today. Under another alias, Esa al-Britani, Barot featured in the official report of the 9/11 Commission. It said that he had been sent by bin Laden and Khalid Sheikh Mohammed, the architect of the atrocities, “to the United States to case potential economic and ‘Jewish’ targets in New York City”.

Barot travelled extensively carrying out reconnaissance missions and setting up “sleeper cells” for al-Qaeda which, despite claims to the contrary, were clearly intact and operational in Pakistan.

His existence was known to security agencies around the world but they did not know his true identity until the summer of 2004.

An intelligence warning in June put Scotland Yard and MI5 on his tail. The discovery of his bombing plans in a police raid in Pakistan convinced the British authorities that they had to arrest him before he could strike.

Barot, always conscious of his neat appearance, was apprehended at gunpoint as he waited in line for a haircut at the Golden Touch barber’s shop in Willesden, northwest London, on August 3, 2004.

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