A member of a British terror cell with alleged links to al-Qaida was involved in a plot to buy a radioactive bomb, the Old Bailey heard.

Salahuddin Amin, 31, had information passed to him about a "radio-isotope bomb" while he was in Pakistan, the court was told.

David Waters, QC, prosecuting, said the plan was to buy the device from the Russian mafia in Belgium.

Amin later told police he did not believe the offer could be genuine.

Amin, from Luton, Bedfordshire, and co-defendant Omar Khyam, from Crawley, are also alleged to have received "detailed" training in Pakistan in how to make the poison ricin.

Along with five other men, all British citizens, they deny plotting to carry out explosions in London using bombs made from ammonium nitrate and aluminium powder.

The conspiracy allegedly involved remote control detonators and 600kg of ammonium nitrate fertiliser and was moving towards its "final phase" when arrests were made in March 2004.

Potential targets discussed by the gang, who already had the components for the bombs, are said to have included "the biggest nightclub in central London", the Bluewater shopping centre in Kent and Britain's power infrastructure.

One defendant had a dozen CD-Roms relating to Transco, which runs the electricity and gas system. Another worked for Morrisons Utility Services, one of Transco's contractors.

Amin's involvement in the alleged nuclear plot was said to have stemmed from an association with Abu Munthir who had visited the same mosque as him in Luton.

Both men later went to Pakistan where Munthir asked Amin to contact another man, Abu Annis, on his behalf.

Mr Waters said: "Amin did so via the internet and Abu Annis said they had made contact with the Russian mafia in Belgium and were trying to buy this bomb.

"Amin told the police he didn't believe this could be genuine. In his own words, he didn't think it was likely 'that you can go and pick an atomic bomb up and use it'.

"Indeed, nothing appears to have come of this. However, it perhaps gives an indication as to Amin's position in the organisation."

In the summer of 2003, Amin and Khyam were said to have attended a camp near Kohat in Pakistan for explosives training and were also instructed in making ricin.

Shortly afterwards Khyam and several other plotters are alleged to have attended a training camp in Malakand.

The court heard they returned to the UK and bought the fertiliser - enough for four or five football pitches - in November 2003 from Bodle Brothers agricultural merchants in Burgess Hill. The buyer said it was for his allotment.

It was stored at a depot in Hanwell, west London.

Khyam, 24, his brother Shujah Mahmood, 19, Waheed Mahmood, 34, and Jawad Akbar, 22, are all from Crawley.

In the dock with them are Amin, 31, from Luton, Anthony Garcia, 23, from Ilford, east London, and Nabeel Hussain, 20, from Horley, near Gatwick.

All seven deny conspiring to cause explosions likely to endanger life between January 1, 2003 and March 31, 2004.

Khyam, Garcia and Hussain also deny possessing an article for terrorism - the fertiliser.

Khyam and Shujah Mahmood also deny possessing aluminium powder for terrorism.

The fine silver powder was found in plastic bags inside a tin behind the garden shed at their family home.

A long list of synagogues, alleged to be "potential targets", was also found there, including several in London and one in Manchester.

Police also discovered a heavily marked book "understanding solid state electronics" and another document titled What to do if contacted by MI5 or Special Branch.

Before the gang could strike, they were bugged in an operation by the security services, leading to the arrests.

On February 22, 2004, Jawad Akbar was recorded talking about attacks on gas, water or electrical supplies and a nightclub.

He allegedly suggested: "The biggest nightclub in central London, no one can put their hands up and say they are innocent - those slags dancing around."

On March 19, 2004, Waheed Mahmood was recorded suggesting "a little explosion at Bluewater."

A Canadian, Mohammed Momin Khawaja, who is awaiting trial there over the plot, allegedly made detonators and then travelled to the UK.

Khyam and Shujah Mahmood met him off an Air Canada flight at Heathrow on February 20, 2004.

They picked him up in Khyam's car, which was already being bugged, as was a flat in Slough, and they discussed a detonator with a range of one of two kilometres.

Khawaja left Heathrow on February 22 and was kept under surveillance when he landed in Toronto.

After planning the "operation" in the UK, Khyam intended to travel to Pakistan before it actually took place, Mr Waters said. He and his brother had booked tickets to Karachi for April 6, 2004.

But unbeknown to the alleged bombers police had already replaced the fertiliser with an inert substance.

Khawaja was arrested on March 29, 2004 and most of the British defendants were held the next day, the jury was told.

The trial was adjourned until today.