Knighthood for author was condemned by a number of Muslim countries and organisations.
Judge Adrian Fulford dismissed the jury on Tuesday after they said they could not agree on a verdict for Asiedu and Yahya.
All six defendants denied the charges, saying the devices were duds and their actions a protest against the Iraq war.
But police and prosecutors said scientific tests proved the bombs were all viable. They do not know why they did not work.
Deputy Assistant Commissioner Peter Clarke, the Metropolitan Police anti-terrorism chief, said the four convicted plotters “set out to replicate the horrors that had been inflicted on Londoners on July 7, 2005.”
“The convictions show that the jury rejected the blatant, indeed ridiculous, lies told by these defendants in a futile attempt to escape justice,” he said