Three men accused of plotting a suicide bomb campaign bigger than 7/7 were secretly recorded saying their explosives would go off "boom", a jury heard today.
Irfan Naseer, Irfan Khalid and Ashik Ali discussed making explosives from household chemicals while under police surveillance last year, it was alleged.
The trio, all from Birmingham, estimated each device would killed around 25 people and maim dozens more if packed with steel nuts, Woolwich Crown Court was told.
Army explosives expert Captain Simon Wilkinson said their conversations showed "professional" understanding of how to make an improvised explosive device.
The bomb would be detonated with the same chemical which killed 52 people in the London bombings of July 2005, the court heard.
That initial explosion would be made far more powerful by a second charge made up of ammonium nitrate - the most common homemade explosive in Afghanistan.
The court heard the defendants discussed using an alarm clock as a timer with one saying "It's gonna go off 'boom'…"
When they discussed the bombs being detonated in a suicide attack instead another allegedly said: "It's gonna be 'bye, bye, bye'".
The court heard the devices were likely to have been no bigger than a packet of cornflakes to fit easily into a rucksack.
Naseer, Khalid and Ali deny preparing acts of terrorism in the UK and other terror offences. The trial continues.