By Chris Summers
Five men have been convicted at the Old Bailey of conspiring to cause explosions in Britain. The trial heard they had enough explosives for a giant bomb.
The target was never settled on, but there was no doubt there was a viable plot and the end result could have resulted in large-scale loss of life.
Expert analysis of the kind of weapon that the convicted conspirators at the heart of the fertiliser bomb plot were making suggests it could have led to a repeat of previous massive terrorist attacks.
"If they had got it right it would have been catastrophic," says Professor Alan Hatcher, who spent 20 years as a bomb disposal expert with the military.
He said the conspirators in what the police called Operation Crevice had all the ingredients for a crude but effective bomb.
They had purchased 600kg of ammonium nitrate fertiliser from a Sussex agricultural merchants in November 2003 and placed it in a self-storage facility in Hanwell, west London.
When mixed with other ingredients including aluminium powder and sugar it would have made a deadly device with devastating consequences in a crowded area.
Prof Hatcher told BBC News: "Ammonium nitrate used to be the weapon of choice of the IRA.
"A 600kg bomb would take a building down and if they had got the mix, the detonators and the timing right, it would have been catastrophic."
The Oklahoma City bombing in 1995 killed 168 people, including 19 children. Timothy McVeigh's bomb contained 2,200kg of ammonium nitrate and fuel oil.
More recently, the US military and FBI explosives experts have been studying the power of such bombs because of their use by insurgent groups in Iraq. The FBI released pictures to the BBC of a training exercise on a weapons range in the United States.
In the exercise, technicians built a bomb with half the fertiliser stored by the British conspirators. Its effects can be seen in the pictures on this page.
Prof Hatcher said he believed the British plotters could have more realistically tried to copy the Bali bombing in 2002, which involved two bombs with a short delay.
"It's a standard tactic to plant a small device which will kill a few people and create panic. They drive people out into the street and then blow them up with the second one," he said.
AMMONIUM NITRATE - THE FACTS
Millions of tons produced each year for use as fertiliser
Sales of the fertiliser are tightly restricted in the EU
Mining companies mix small amounts of explosive grade ammonium nitrate with fuel oil to create explosives
Used in several IRA bombings
Also used in the Bali and Oklahoma City bombings
Source: New Scientist
Such a tactic could have had horrendous consequences at Bluewater shopping centre in Kent or the Ministry of Sound nightclub in London, both of which were mentioned by the plotters as potential targets.
As well as the ammonium nitrate, police also found a small quantity of aluminium powder at Khyam's home address in Crawley although the prosecution later conceded it was not enough to set off a 600kg device.
Prof Hatcher said only fairly small amounts of aluminium powder were needed to make an improvised explosive device (IED).
Lawyers for the prosecution was never able to show the jury one of these IEDs but the trial heard evidence about how the gang had handled detonators while in Pakistan.
The plotters also needed a remote-control device to set off the bomb - and the man allegedly charged with designing this device was Canadian IT expert Mohammed Momin Khawaja.
Investigators allege they found circuit boards, a home-made radio transmitter and matching receiver board at his home following his arrest. He is currently awaiting trial in Canada.
'Impossible to legislate'
So if ammonium nitrate is so dangerous why is its sale not restricted, like some other substances?
A Home Office spokesman said: "A wide range of chemicals (and other substances) with perfectly legitimate purposes are present in many forms in our everyday lives.
"While it is possible for these to be used to manufacture explosives or other dangerous chemicals, to legislate in ways which would put them completely beyond the reach of individuals determined to employ such means would be impracticable."
In recent years the police and MI5 have been working hard to build up relationships with manufacturers, wholesalers and importers to educate them about the dangers and to urge them to be aware of suspicious sales.
The plotters bought the fertiliser from agricultural merchants Bodle Brothers in Burgess Hill, Sussex.
A spokesman for Bodle Brothers said: "Why did we sell the bag to them? Because they wanted to buy it. That's what we do."