Waheed Mahmood, 34, and Jawad Akbar, 23, also of Crawley; Salahuddin Amin, 31, of Luton, Bedfordshire; and Anthony Garcia, 24, of Barkingside, east London, were also found guilty. They were sentenced to life with a minimum of 40, 35 and 40 years respectively.
Two other men, Shujah Mahmood, who is Khyam's brother, and Nabeel Hussain, have been found not guilty.
During the trial, which lasted a year, it emerged that the five men had been involved in planning to use large quantities of ammonium nitrate fertiliser to make explosives.
They attended a terrorist training camp in Pakistan in 2003, where they were taught to make explosives, Deputy Assistant Commissioner Peter Clarke, head of the Metropolitan Police Service counter terrorism command and national coordinator of terrorism investigation, said.
"This case marked a new stage in our understanding of the threat posed by al-Qaida to this country," he said.
"This was not a group of youthful idealists. They were trained, dedicated, ruthless terrorists who were obviously planning to carry out an attack against the British public."
Targets nominated by the plotters included the Bluewater shopping centre in Kent, the Ministry of Sound nightclub in central London and the country's gas network.
The court heard how the planned explosions could have killed hundreds.
It also emerged today that the plotters had links with some of those involved in the July 7th London bombings, which killed 52 people in the capital.
Police arrested the men in 2004 – about 16 months before the London bombings.
The Old Bailey jury were not informed that Mohammed Sidique Khan, who is widely considered the driving force behind the July 7th attacks, was seen with Khyam during the time he was being monitored by security services.
Khan was not considered a security threat at that time.
Commenting on today's verdicts, home secretary John Reid said: "Five dangerous terrorists are now behind bars thanks to the hard work of our police and security services.
"I want to thank the men and women in the police and security service who have worked extremely hard to ensure the perpetrators of this plot have been brought to justice and a major terrorist attack that could have killed and injured many people has been averted."
He added: "Today's case reminds us all that the terrorist threat we face is real and severe. I want to take time now to reflect on the verdicts."
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