Three men who tried to procure a dangerous chemical which could have been used by terrorists did not realise they were being set up, a court heard.
The men believed red mercury was dangerous, the court heard
Mark Ellison, prosecuting, said they did not know the man they were negotiating with over the "red mercury" was a News of the World journalist.
Jurors heard Mazher Mahmood, alias the "fake sheikh", was working with police.
Dominic Martins, Roque Fernandes and Abdurahman Kanyare denied three charges at the Old Bailey.
Mr Fernandes, 44, and Mr Kanyare, 53, both of Edgware, north-west London, and Dominic Martins, 45, of Stanmore, north-west London, pleaded not guilty to two charges of trying to set up funding or property for terrorism.
They also denied one charge of having "a highly dangerous mercury based substance" for terrorism.
Mr Ellison told the jury red mercury was believed to be a material which could cause a large explosion, possibly even a nuclear reaction.
He told the court there were different descriptions of the substance described as red mercury. But he added: "The Crown's position is that whether red mercury does or does not exist is irrelevant."
He warned the jury not to get "hung up" on whether red mercury actually existed at all.
Mr Ellison said the fact was that the three defendants had hit upon a meaning for it as a substance which was highly dangerous and expensive, and they pursued it.
He told the court they met Mr Mahmood, who was posing as "Mohammed", a man who claimed to be able to supply the red mercury.
Mr Ellison accepted there was controversy about Mr Mahmood's methods and said the defence could well try to claim the defendants were the victims of entrapment.
The court was told that scientists were divided as to whether red mercury actually existed.
Mr Martins allegedly searched on the internet and discovered information on the About.com website about red mercury
There are various theories about what red mercury is, one of which is that simply means any red-coloured mercury originating in Russia
As for its powers, it is variously described as being radioactive or toxic, and to be explosive when under high pressure, the court heard.
Mr Ellison said the going rate for red mercury was said to be around $300,000 per kilo.
The defendants told him Mr Kanyare had a buyer in the Middle East who was willing to pay up to £500,000 for the red mercury, the court heard.
Mr Ellison said Mr Fernandes and Mr Martins were "middle-men" who hoped to be paid a healthy commission for finding the red mercury for Mr Kanyare, who was described as a Somali-born "buyer and seller of commodities".
Mr Ellison said: "Each of them knew that the intended customer wanted the substance for use in terrorism."
He added: "Each was aware that not only would the substance be changing hands for hundreds of thousands of pounds, but also that it was a highly dangerous, radioactive, explosive or toxic substance - the sort of thing being sought for use in acts of terrorism."
Mr Mahmood was later joined by undercover police who met Mr Kanyare, an international dealer who was said to have a contact in the Gulf who wanted to buy the substance.
Mr Kanyare allegedly told Mr Mahmood he would "travel anywhere in Western Europe" to test the substance and his buyer would then pay cash for it.
He also said he wanted to use something like a Geiger counter to test that it was genuine.
But he was apparently unimpressed by the sellers and allegedly told Mr Martins he thought he was dealing "with a bunch of con men", the court heard.
The final meeting, set up by Mr Mahmood, was at the Holiday Inn in Brent Cross, north London, where the defendants were arrested.
The sting began after Mr Mahmood was contacted by Mr Martins' former brother-in-law, known as Mr B, who had turned to his newspaper after being disappointed with the response he received after reporting Mr Martins to police, said Mr Ellison.
He said the defendants may have become involved in the scheme because of the prospect of making money but that they all knew that terrorists would be interested.
Mr Martins told police after his arrest: "I am just a go-between. The guy phoned me and asked if I knew anyone who could get red mercury. I tried to arrange it because I am in so much debt."
Mr Ellison said Mr Martins and Mr Fernandes had £10,000 worth of debts and had tried various schemes to try to make money.
The trial continues.