Three men are on trial in Birmingham, England, accused of planning a bombing campaign in Britain that could have been deadlier than the London bombings on 7 July, 2005.
Prosecutors told the jury at at Woolwich Crown Court that two of them had recorded suicide videos while undergoing terrorism training in Pakistan, that would have been played to the world had their plot been completed.
The accused are Irfan Naseer, 31, Irfan Khalid and Ashik Ali, both 27, who deny engaging in conduct in preparation of terrorist acts.
The charges relate to the period between December 2010 and September 2011.
Prosectuor Brian Altman QC said the defendants were proposing to detonate up to eight rucksack bombs in a suicide attack and/or to detonate bombs on timers in crowded areas in order to cause mass deaths and casualties."
the court heard, Mr Naseer and Mr Khalid returned from Pakistan in July 2011, and Mr Ali provided them with a "safe house" in which they could experiment with chemicals.
A listening device was placed inside the flat - and two more in vehicles used by the men. The recordings of the mens' conversations will form the heart of the prosecution.
The trial continues.