The alleged 21 July attacks were not a failed suicide mission but a "protest" with an escape plan, a court has heard.
Muktar Ibrahim and the other accused deny the charges
Muktar Said Ibrahim, 29, told Woolwich Crown Court the accused were told to stand near Tube doors to escape and not leave anything to identify them.
Mr Ibrahim told the jury he could "not explain" why co-defendant Hussain Osman left his gym membership card in a rucksack with a failed device.
Six men deny conspiracy to murder and to cause explosions.
They are accused of attacking London's transport network on 21 July 2005.
Mr Ibrahim has previously admitted carrying a device found by police but said he did not intend to cause an explosion.
Asked by prosecutors why Mr Osman left the gym membership card in a rucksack, he said: "I cannot explain that.
"I had no idea he did that, all I can say is that he forgot."
Junior prosecution counsel Max Hill asked: "He forgot? Was there much else to think about?"
Mr Hill told the jury that Mr Ibrahim and the other defendants had made no plan to escape.
"You didn't care, nor did your other defendants," Mr Hill said.
"That's not true," Ibrahim replied.
Mr Hill responded: "You didn't expect to survive, you and all your co-defendants expected to perish in the inferno.
"That's why it didn't matter in the least whether there were identity documents because they would all go up in flames."
"That's not true," Mr Ibrahim repeated.
Mr Ibrahim, of Stoke Newington, north London, is accused along with Mr Ramzi Mohammed, 25,; Mr Yassin Omar, 26, of New Southgate, north London; Mr Manfo Kwaku Asiedu, 33, and Mr Hussein Osman 28, both of no fixed address; and Adel Yahya, 24, of Tottenham, north London.
The trial continues.