Five people have been convicted of conspiracy to cause explosions following the discovery of 600kg of ammonium nitrate fertiliser at a lock-up in west London in 2004. Fertiliser has been used by terrorists for several decades.
Ammonium nitrate, seen here in Pakistan, can be lethal
Britain probably has more experience of dealing with bombs made from fertiliser than any other country in the world.
For three decades it was the explosive of choice for Irish republicans bombing British targets, leading to restrictions on the sale of fertilisers based on ammonium nitrate and an outright ban on the sale of the chemical itself within Northern Ireland.
But throughout the Troubles, ammonium nitrate-based fertilisers continued to be widely available and an easily accessible raw material throughout the rest of the UK.
That has changed in recent years - largely as a result of the find in 2004 in a lock-up at Hanwell, west London.
The so-called Operation Crevice trial at the Old Bailey heard of a plot to use it for a bombing campaign in England.
Industry sources say fertiliser manufacturers, importers and merchants were left with a stark choice - to ensure they guarded their supplies better or face draconian restrictions, maybe even a total ban on certain types of farm chemicals, to stop them falling into the wrong hands.
Proof of identity
"A ban would leave the UK farming industry at a severe disadvantage and we didn't want to have to deal with onerous rules and regulations imposed on us," says John Kelley, of the Agricultural Industries Confederation.
What it came up with was the Fertiliser Industry Assurance Scheme, which has so far signed up more than a hundred firms since its launch in January 2006.
Those involved in the sale of fertilisers, for example, are supposed to sell the most dangerous chemicals only to those who have accounts with them, or customers who provide them with proof of identity.
Firms who register with the scheme have to submit to an "external audit" of the way they run their business.
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With Britain either importing or manufacturing 4m out of the 23m tons of the fertiliser produced in the world each year, the industry was keen to avoid having to work to rules imposed on it from outside.
"This was seen as the best option really," says Mr Kelley.
"In some firms it will be seen as more cost and more bureaucracy, but it's better the codes of practice are written by the industry for the industry."
Those working on the land are also being told they have to take more care of the fertiliser they use.
The National Counter-Terrorism Security Office has targeted farmers in a campaign to get them to keep fertilisers under lock and key.
A 10-point plan warns against storing supplies close to public roads and leaving bags of fertilisers out in fields ready for use.
Farmers are warned to tighten security around fertiliser stocks
"Awareness certainly has increased over the last 18 months," says Alex Dinsdale, of the National Farmers' Union.
"There's been a steady stream of information coming out to farmers, with leaflets and bags of fertilisers now carrying the address for the government's 'secure your fertiliser' website.'"
It is also being stressed to those who work in agriculture that they need to report any losses or thefts of fertiliser to the police.
Other countries, including Spain and Australia, have already changed the law on handling ammonium nitrate and the United States is looking set to follow a similar route.
It certainly continues to be a major concern with the security forces here.
"This kind of explosive is powerful, don't be fooled," one bomb expert working with the security services told the BBC News website.
"It's got about 80-90% of the explosive force of TNT and about half of that of Semtex, so the terrorists just use more of it."
Unlike other chemicals that can be used to manufacture explosives, the fertiliser is a lot more stable and the actual processes involved are a lot simpler, he explained.
Despite the implied threat to the agricultural industry of an outright ban, ministers also know that would be unlikely to stop future bombings using similar explosives.
Experts point to the switch to fertilisers based on the "safer" compound of calcium ammonium nitrate in Northern Ireland in response to the republican bombers.
"Four weeks later the IRA figured out how to make a bomb using that," says one veteran of the anti-terrorist campaign.
But further regulation has not been ruled out by the government in an attempt to close down the ability of terrorists to get their hands on these potentially lethal supplies for good.
The Department for Environment, Food and Rural Affairs says it has been monitoring the current self-regulated regime.
A full-scale review into its effectiveness is already planned for the summer.
A spokesman for Defra said: "If it is found not to be effective then we may need to consider a range of alternatives, one of which may be regulation."