LONDON—Prosecutors say three British Muslim men accused of plotting a mass casualty attack were recorded discussing how to make bombs more deadly and criticizing the London transit bombers for not putting nails in their devices.

Transcripts read in court Friday allegedly feature Irfan Naseer, Irfan Khalid and Ashik Ali talking about the July 7, 2005, bombings.

Naseer allegedly agrees with another man that not enough damage had been done in the bombings, which killed 52 commuters.

Naseer is alleged to have said the four suicide bombers "didn't put the nails and stuff in, man."

Prosecutors allege the suspects are members of a homegrown terror cell inspired by the anti-Western sermons of U.S.-born Islamist cleric Anwar al-Awlaki, who was killed in Yemen last year.

The men deny the charges.