Jury shown gas explosions mock-up

The men, one of whom cannot be pictured, deny all the charges

Jurors in the trial of seven men accused of involvement in a bomb plot were shown footage of mocked-up explosions on a gas pipeline network.

The Old Bailey heard such an explosion could cause mushroom clouds and sparked fires more than 300 metres away.

All of the men deny conspiring to cause explosions and four also deny having chemicals suitable for bomb-making.

They are accused of plotting to carry out a half-tonne fertiliser bomb attack against an unidentified target.

It is alleged the possible targets discussed were pubs, clubs, shopping centres and the gas network.

One of the alleged conspirators is said to have worked for a contractor for gas maintenance company Transco, and is accused of having a CD-Rom on his home computer with details of the UK's gas pipeline network.

National Grid Transco runs the high voltage electricity network in England and Wales and Britain's high-pressure gas infrastructure.

The reconstruction was designed to show the effects of explosive devices that could be used by terrorists.

National Grid engineers used plastic explosives and then recreated a homemade bomb consisting of ammonium nitrate fertiliser and diesel fuel.

Three hundred yards away from the fracture of the pipeline was damage caused by debris and there were lots of secondary fires, fires that were created by the heat of the first fire Gas engineer Dr John Evans

Gas engineer Dr John Evans, who works for research company Advantica, said a homemade 500kg fertiliser bomb had the same effect as 1kg of plastic explosives.

"With ammonium nitrate or homemade explosives it is more difficult to get that same effect.

"If you increase the amount of explosives, it will almost certainly fail that pipeline in that way.

"Three hundred yards away from the fracture of the pipeline was damage caused by debris and there were lots of secondary fires, fires that were created by the heat of the first fire."

He said the would create a fireball, but would not ignite the gas along the pipeline because it would need to be mixed with air.

It is alleged the men plotted between 1 January 2001 and 31 March 2004 to set off a series of bombs.

Omar Khyam, 24, his younger brother Shujah-Ud-Din Mahmood, 18, and Waheed Mahmood, 33, from Crawley, West Sussex, along with Jawad Akbar, 22, from Crawley and Uxbridge, Anthony Garcia, 27, from Ilford, east London, Nabeel Hussain, 20, from Horley, Surrey, and Salahuddin Amin, 30, from Luton, Bedfordshire, are accused of conspiring to cause an explosion likely to endanger life contrary to section 3 (1)(a) of the Explosive Substances Act 1883.

Mr Khyam, who has also lived in Slough, Mr Garcia and Mr Hussain are also charged under the Terrorism Act 2000 of possessing an article for terrorism - namely 600kg of ammonium nitrate fertiliser between 5 November, 2003 and 31 March, 2004.

Brothers Mr Khyam and Mr Mahmood also deny having aluminium powder, which is an ingredient in explosives, between the said dates.