A British al Qaida cell was facing massive jail sentences today for plotting a bombing campaign against the UK to rival the 9/11 terror attacks.

The radical Islamic group's leader, Omar Khyam, was found guilty of conspiracy to cause explosions likely to endanger life following a year-long £50 million Old Bailey trial.

The plan was to use 600kg of ammonium nitrate fertiliser as the basic ingredient for a bomb attack on a busy nightclub or shopping centre that would have killed hundreds of innocent British civilians.

Today's convictions were immediately overshadowed by the revelations about the terror cell's links to the July 7 bombers.

It can now be revealed that Mohammed Sidique Khan, the ringleader of 7/7 was a close associate of Omar Khyam when he was one of Britain's top terror targets and in the final stages of his plotting.

Khyam also met another of the July 7 bombers, Shehzad Tanweer.

Despite this, both Khan and Tanweer were dismissed as peripheral figures by the police and MI5 and not fully investigated. Within 16 months they led a wave of suicide bombings in London that killed 52 innocent people.

In the wake of the revelations, politicians, grieving relatives and survivors of the blasts all called for an independent inquiry into the failings that allowed the July 7 cell to slip through the net.

The fertiliser plot is one of the biggest terrorist conspiracies ever foiled by the police and security services in Britain, while the investigation into it was, at the time, the largest anti-terrorism operation ever mounted.

Before the court with Khyam were his brother Shujah Mahmood, 20; Waheed Mahmood, 35; and Jawad Akbar, 23, all from Crawley; Anthony Garcia, 25, of Barkingside, east London; Nabeel Hussain, 22, of Horley, Surrey; and Salahuddin Amin, 32, of Luton, Bedfordshire.

They denied conspiring to cause explosions likely to endanger life between January 1 2003 and March 31 2004.

Khyam, Garcia and Hussain also denied a charge under the Terrorism Act of possessing 600kgs (1,300lbs) of ammonium nitrate fertiliser for terrorism.

Khyam and Shujah Mahmood further denied possessing aluminium powder for terrorism.

The defendants denied there was a plot. Some said they did not know what the fertiliser was, that they were only interested in sending money and supplies to fighters in Kashmir and Afghanistan, or that they were duped.

The jury of seven men and five women were out for a record number of days and were in the seventh week of deliberations.

Garcia, Akbar, Waheed Mahmood and Amin were convicted with Khyam of conspiracy to cause explosions likely to endanger life.

Hussain and Shujah Mahmood were cleared of conspiracy to cause explosions.

Khyam and Garcia were also found guilty of possession of 600kg of ammonium nitrate fertiliser for terrorism, but Hussain was cleared.

Khyam was also found guilty of possession aluminium powder for terrorism, but Shujah Mahmood was found not guilty.

The defendants looked relaxed and were smiling as they were led into the court.

But they became stony-faced and looked tense as the foreman stood to deliver the verdicts after a record of nearly 135 hours of deliberation, over 27 days.

The jury foreman spoke in a soft voice to say they had found five of the seven defendants guilty of conspiracy.

Those found guilty showed no reaction but there was a sigh of relief as the youngest defendant, Shujah Mahmood, was cleared of all charges.

He was told he would be released and wiped an eye as he was led to the cells to complete the formalities.

The other defendants said goodbye to him as he left.

Nabeel Hussain immediately bent down to the floor after he was cleared.

He then got up and leaned on his chair as he waited for the second verdict on him. He then looked up to the skies when he was told he was found not guilty. The judge said he could leave the dock.

Nabeel had been on conditional bail and had always said he had been duped into using his credit card to buy the fertiliser.

Shujah had told the court that he was only 17 at the time of the conspiracy and had been in the shadow of his older brother Khyam.

Waheed Mahmood immediately sat down after he was found guilty. He had refused to stand up for the judge throughout the case and was the only defendant to give evidence.

The judge Sir Michael Astill rejected defence claims that the plot was incomplete.

The judge said: "I do not take the view that this was an abandoned conspiracy.

"This was a conspiracy that did not come to fruition, no doubt because of the intervention of the security services."

The judge said that he considered that the terrorists had chosen targets which included the Ministry of Sound nightclub.

He added: "They were in the debate. They were in the mix. They were the sort of targets they were looking for."

Sir Michael said that not everything about the conspiracy had been discovered by the police.

He said: "Of course it's common sense that police investigating matters of this sort, they never find out everything.

"Just because other ingredients were not found, it does not mean they did not exist.

"There was completed, to be put together in a short time, an explosive device which they knew would work."