The use of rucksack explosives on the Tube in 2005 was inspired by protests by Fathers4Justice, one of the bomb plot suspects has told a court.
Mr Omar and five other men deny conspiracy to murder
Yassin Omar, 26, from north London, admitted setting off a rucksack device in London in protest at the Iraq war.
But he told Woolwich Crown Court he had been copying a flour protest in the Commons by the fathers' rights group and had not intended to kill anyone.
All six men on trial deny conspiracy to murder and to cause explosions.
Mr Omar, the so-called Warren Street bomber, from New Southgate, insisted it had "never crossed my mind" that anyone might be injured by their devices.
He entered the witness box for the first time, becoming the third defendant to give evidence, after co-defendant Hussain Osman decided against defending himself in court.
Mr Omar said it had been his idea to come up with something dramatic as a public protest against the "illegal" war in Iraq.
He said the Fathers4Justice protest - in which purple flour was thrown over the prime minister during Question Time in the Commons in May 2004 - had been the inspiration and made him think chapatti flour could be used as part of their demonstration.
"I was thinking of some way to get the government's attention. The best example was Fathers4Justice and I thought I would try something like that," he said.
"Since Fathers4Justice used flour we decided we were going to use flour as well - that's where the idea came from."
Mr Omar said his first thought had been to use a firecracker to scare people but, with the help of co-defendant Muktar Said Ibrahim, the explosive developed into a hydrogen peroxide-based device.
Mr Omar, who was seen fleeing London in a burka the day after the attacks in 2005, said: "I intended the detonator to go off and only to make a popping noise.
"It happened exactly as I expected. I thought... the only thing that could happen was that the rucksack might split."
When asked to elaborate on why he was protesting against the war in Iraq, Somalia-born Mr Omar said: "Because of the suffering of people and deaths of innocent people.
"I hoped that this would be televised, would be shown on TV and taken seriously and that would put pressure on the government after they realised that people have gone to these lengths just to do a demonstration on Iraq.
"In due course the public would be talking about it. We hoped that the government would change its foreign policy and pull troops out of this illegal war."
He added: "I did not intend to hurt nobody and didn't intend to kill myself."
Mr Omar and Mr Osman, 28, of no fixed address, are on trial with Muktar Said Ibrahim, 29, from Stoke Newington, north London, Ramzi Mohammed, 25, of North Kensington, west London, Adel Yahya, 24, of High Road, Tottenham, north London, and Manfo Kwaku Asiedu, 34, of no fixed address.
The trial continues.