The leader of a British al-Qaeda cell has been jailed for at least 20 years for plotting a bombing campaign to rival the September 11 terror attacks.

Omar Khyam, from Crawley, was an associate of July 7 plot ringleader Mohammed Sidique Khan and boasted of taking orders from al-Qaeda chief Abdul Hadi, number three in the terror organisation.

Khyam, 25, and four others were yesterday found guilty of conspiracy to cause explosions after a record-breaking year-long trial at the Old Bailey.

His four henchmen were also given life sentences for their part in the terror plot and warned they may spend the rest of their lives in jail.

The judge, Sir Michael Astill, told the terror plotters: "You have betrayed the country that has given you every opportunity."

He added: "All of you may never be released. It is not a foregone conclusion."

The plan was to use 600kg (1,300lb) of ammonium nitrate fertiliser as the basic ingredient for a bomb attack on a busy nightclub or shopping centre that would have killed hundreds.

The arrests of the Crawley-based gang in 2004 were the first since al-Qaeda decided to bring terror to Britain.

But after yesterday's verdicts there were demands for an official inquiry as it emerged that the security services came across Khan and fellow July 7 suicide bomber Shehzad Tanweer while investigating the Crawley men.

Khyam was a close associate of Khan and also met Tanweer but they were dismissed at the time as peripheral figures.

Within 16 months the pair and two other men took part in a series of attacks on London's transport system, killing themselves and 52 others.

Waheed Mahmood, 35, and Jawad Akbar, 23, from Crawley, were found guilty with Khyam of conspiracy to cause explosions likely to endanger life between January 1, 2003, and March 31, 2004.

Anthony Garcia, 25, of Barkingside, east London, and Salahuddin Amin, 32, from Luton, were also convicted of the conspiracy.

Khyam and Garcia were also found guilty of having 600kg of ammonium nitrate fertiliser for terrorism.

The jury convicted Khyam of a further count of having aluminium for terrorism.

Shujah Mahmood, 20, from Crawley, and Nabeel Hussain, 22, of Horley, Surrey, were both cleared of the conspiracy.

Mahmood was also cleared of possessing aluminium powder and Hussain of having ammonium nitrate.

Khyam, Garcia and Waheed Mahmood were told they would serve at least 20 years of a life sentence.

Amin and Akbar were told they would have to serve a minimum of 17- and-a-half years of their life sentences.

The judge also imposed concurrent eight-year sentences on those convicted of having the ammonium nitrate and aluminium powder.

Sir Michael warned the defendants it was by no means guaranteed that they would ever leave prison.

He said: "It may be that some or all of you will never be released and there must be no misunderstanding about it."

Only Akbar returned to court for sentencing. The others, their lawyers told the judge, all refused to go back into the dock.

The judge said he would address them as if they were all there. He told them: "You have betrayed the country that has given you every advantage in life."

The "spiral of contamination" began with the "preachers of hate who contaminate impressionable young minds," he said.

The judge told Khayam: "You are ruthless, devious, artful and dangerous."

He told Garcia: "You turned your murderous ambition on the UK."

Akbar had been willing to bomb the Ministry of Sound nightclub and had demonstrated "intelligence and disturbing deviousness".

The judge told him: "You are dangerous and the public requires protection from you."

Waheed had been willing to bomb the Bluewater shopping centre the next day. "You exerted authority over others," the judge told him.

He told Amin: "The focus of your life was your support for terrorism."

Sir Michael, referring to "the teachers and preachers of hatred and revenge who so often lurk in the shadows," added: "Those who begin the process do not put themselves forward.

"They are masters of cowardice. They, like you, insult the numerous followers of the Islamic faith who enrich this society but who attract unmerited suspicions because of you, simply because of their faith."

Sir Michael thanked the seven men and five women of the jury and excused them from further jury service for life.

He said of their record 27 days of deliberations: "I have never seen such devotion to duty."

The judge also commended the officers who conducted the inquiry "with commendable thoroughness and expertise".

Sir Michael said the plotters had targeted sites such as Bluewater shopping centre and the Ministry of Sound nightclub "where numerous members of the public congregate and become vulnerable."

The fact they had contemplated these targets "demonstrates the scale of suffering and horror that you were prepared to inflict and would have inflicted but for the intervention of the security services and the police."

The judge continued: "It may be that you consider yourselves heroes of the cause that you espouse.

"But you are considered by the vast majority of the population of whatever religious faith, or none, as nothing but cruel and ruthless misfits who should be removed from society for its own protection."

He told Khyam: "You were the energy behind the conspiracy. You involved others by bringing them into the plan."

Garcia, he said, was the "personal assistant and close confidant of Khyam".

Amin's solicitor Tayad Ali read a statement in which he continued to protest his innocence. He said: "An outrageous confidence trick has been played on the jury and against me."

Amin claimed he had been tortured and mistreated by the intelligence services in Pakistan while he was held in the country during 2004.

"Even though I am a British citizen, the British Government did not lift a finger to protect me from abuse and torture."

Amin described the war on terror as "misguided" and demanded that the "truth" about what happened to people in secret detention be made public.

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To see a video of Omar Khyam inspecting the chemical fertiliser he intended to use to in a major campaign of terror, click here.