Prosecutors began to lay out the second day of their case against the men, whom they allege formed a terrorist cell which planned to carry out synchronised attacks on three London Underground trains and a bus.

Britain's highest-security court continued to hear details of the alleged plot to commit mass murder on July 21, 2005, exactly two weeks on from the first suicide attacks in Britain on July 7 which killed 56 people.

Judge Adrian Fulford opened Tuesday's proceedings by warning the jury that they should ignore coverage of the high-profile trial.

"You must close your minds completely to the media and focus solely on what happens in the court room," he told the nine women and three men.

On the opening day, the group were alleged to have made bombs out of chapati flour, hydrogen peroxide, acetone and acid and packed with nails and screws to maximise "devastation", Woolwich Crown Court in southeast London heard.

In what is likely to become one of the most high-profile cases involving alleged terrorism seen in Britain, the accused deny charges of conspiracy to murder and conspiracy to cause explosions likely to endanger life.

The trial of Muktar Said Ibrahim, 28, Manfo Kwaku Asiedu, 32, Hussain Osman, 28, Yassin Omar, 26, Ramzi Mohammed, 25, and Adel Yahya, 24, all originally from Africa, is expected to take up to four months.

"This case is concerned with an extremist Muslim plot, the ultimate objective of which was to carry out a number of murderous suicide bombings on the public transport system in London," prosecution lawyer Nigel Sweeney said Monday.

He said the conspiracy had been in existence long before the July 7 bombings and was not some "hastily arranged copycat".