Salahuddin Amin, 31, contacted an intermediary about the purchase of a radioisotope bomb and was told it could be supplied by Russian mafia criminals based in Belgium, prosecutor David Waters told London's Central Criminal Court on Wednesday.
Waters said Amin had been instructed to carry out negotiations by a man he had met at alleged terrorist training camps in Pakistan.
Amin and six other men are accused of conspiring to cause explosions and had drawn up a long list of potential bombing targets, including Britain's electricity network, one of London's biggest nightclubs and one of the country's largest shopping malls.
Omar Khyam, 24; Anthony Garcia, 24; Nabel Hussain, 20; Jawad Akbar, 22; Waheed Mahmood, 33; Shujah ud Din Mahmood, 19; and Amin, all deny the charge and face life imprisonment if convicted.
Waters said nothing came of the group's interest in a radioisotope bomb and that, in a police interview, Amin said he didn't think it was likely "you can go and pick an atomic bomb up and use it".
Britain's security services and anti-terrorism police put the men under surveillance in February 2004, recording a conversation during which Akbar proposed attacks on "gas, water or electrical supplies", or a large nightclub, Waters told the jury.
Listening devices recorded Waheed Mahmood suggesting a "little explosion at Bluewater - tomorrow if you want", referring to the Bluewater shopping mall in Kent, southern England, one of the biggest retail centres in the country.
In a raid on the home of Khyam and his brother, Shujah ud Din Mahmood, police recovered a list of synagogues in London and Manchester, Northern England, which were also potential targets, Waters said.
He said that during a raid on Hussain's flat at Brunel University, in London, police seized CD ROMs which contained detailed plans of Britain's electricity and gas supply network, oil pipelines and high voltage cables.
Waters told the jury that in October or November 2003, Garcia had ordered 600kg of ammonium nitrate fertiliser, saying it was for a small garden plot he kept.
To use all the material as a fertiliser, his allotment would need to be "the size of four or five football pitches", Waters said.
Waters told the court that Mohammed Momin Khawaja, a Canadian computer worker, aided the plot by developing a remote detonator and a mobile phone sized jamming device - which could be used to ensure a bomb doesn't explode accidentally.
Khawaja was arrested the following month and is awaiting trial in Ottawa, Waters said.
Six of the defendants were arrested in and around London in March 2004, when police also seized 600kg of ammonium nitrate fertiliser - about one-third of the amount used in the 1995 Oklahoma City bombing, which killed 168 people.
Amin, who was born in Pakistan but is a British citizen, was arrested a month later in Pakistan.