Bereaved relatives and survivors of the July 7 terror attacks said the case for an independent inquiry into the atrocity was now "overwhelming" in the wake of the revelations about MI5's prior knowledge of the bombers.

Rachel North, who survived the blast on the Piccadilly Line train, said she was shocked and appalled when she first learned that the ringleader, Mohammed Sidique Khan, had been a close associate of Omar Khyam, the man convicted today of plotting a massive fertiliser bomb attack on UK soil.

Like many, she believed the Government and security officials when they said in the immediate aftermath of 7/7 that nothing had been known about those responsible and that nothing could have been done to prevent it.

When that illusion was shattered, it came as a massive shock.

"I remember that Charles Clarke (the then home secretary) came out and said 'these bombings came out of the blue, these men are clean skins'," she said.

"It was tempting to believe that these guys had never been known to the police or the security services, that they had somehow managed to make these bombs and drive down to London and get on Tube trains and a bus, and that it was a terrible tragedy and there was nothing anybody could have done to stop them.

"When it transpired that was not the case, it was devastating.

"This has fuelled my desire for an independent inquiry (into the bombings) because it appears we have not been told the truth about what happened and what we knew about these bombers prior to 7/7."

Asked if, in light of the revelations, it now looked as if the bombings could have been prevented, she replied: "It looks as if ... yes.

"The first bad mistake was that it should have been clear to anybody familiar with the behavioural profile of UK jihadists that these guys (Khan and his right hand man Shehzad Tanweer) ticked loads of boxes.

"They were driving around with terrorists, they were engaged in criminal activity to raise money, they were known to be fans of extremist preachers, they had been abroad and trained to bring the battle to the UK, they were hanging around with people planning a bomb plot - they were right at the top of the scale.

"I understand it is impossible to track every single person who might be expressing support for jihad, but these people were certainly not clean skins.

"Until we know exactly what was known about these people, how are we supposed to have trust and confidence in the Government and the security service?

"I understand that people are human and make mistakes - and if they are the best and brightest people they should stay in their jobs - but they should demonstrate that they are capable of learning."

Ms North called for an independent inquiry with the power to subpoena witnesses.

"It is not about blame. It is about having trust and confidence in the people paid to protect us," she said.

"If we had an independent inquiry, it would help us understand the nature of the threat. People need to feel that it is explainable and containable. I also think it would do a lot to counter Islamophobia.

"I know a lot of Muslims are supportive of an independent inquiry.

"The public need to know what was known about these bombers, what and why it happened and what is being done to stop similar things happening again."

:: Graham Foulkes, who lost his 22-year-old son David, a media sales manager for The Guardian in Manchester, in the Edgware Road blast, said when he learned of the truth about 7/7 he was "absolutely overwhelmed with a sense of sheer disbelief".

"The consequences of that level of incompetence were such that my son was killed. That is truly appalling," he said.

Could the bombings have been prevented? "As a father who lost a son, I am drawn to that conclusion - if I put my cold head on, I do not know," he said.

Khan, he said, had appeared on the intelligence services' radar as far back as 1999 when he went to Pakistan. It was also now known that he had been to Afghanistan, where he had contact with senior al Qaida figures.

"I think John Reid (the current Home Secretary) summed it up when he said his department was not fit for purpose," Mr Foulkes said.

"If you look at the anti-terrorist structure in this country, it is made up of at least seven different organisations - each with their own command and control structure.

"By not having an inquiry, we are saying that we accept a system that is not fit for purpose, that does not work."

Mr Foulkes described the current set-up as "archaic".

"Terrorist activity is here and now, yet we have a team that has been cobbled together from the remnants of the Cold War, the police and Special Branch."

Adding his voice to those calling for an an independent inquiry, he continued: "The rationale for an inquiry is now overwhelming.

"July 7 showed the devastating consequences of the system not being fit for purpose, and yet by not holding an inquiry, John Reid has shown he is happy with the current system - one that is not fit for purpose.

"I find it beyond my understanding that he has not called an inquiry."

Mr Foulkes, like most others affected by the blasts, feels that they and the public have been misled over 7/7.

"Massively so... we were told that the bombers were clean skins, that it was impossible to detect home-grown terrorists," he said.

"That was clearly not true. Of course I feel misled, of course I feel like we've had the wool pulled over our eyes.

"What is worse is that the system has not changed. These are people's lives and families absolutely destroyed. It is hugely frustrating."

On Dame Eliza Manningham-Buller's departure from the top job at MI5, he said: "She has fallen on her sword. I think she jumped before an inquiry was held, which undoubtedly would have criticised her personally.

"I would have demanded a face-to-face meeting for an explanation. It is not acceptable in this day and age to have such a poorly-organised, poorly-managed department.

"We are not talking about pushing paper around. We are talking about dozens of lives being lost and dozens of families being destroyed.

"It is the responsibility of the Government to acknowledge that the system is wrong and to fix it, but they steadfastly refuse to do that."

:: Nader Mozakka, who lost his wife Behnaz in the King's Cross blast, said: "I always had a suspicion there was more to it than they told us at the time.

"I have been through so many hoops, trying to put pressure on them to get an inquiry. That is the only way forward. We need to know exactly what happened."

Iranian-born Mrs Mozakka, a 47-year-old mother of two, was a biomedical officer at London's famous Great Ormond Street Children's Hospital and lived in Finchley.

Mr Mozakka said it now appeared that despite what he had been told during numerous meetings with high level officials and politicians, that the security services "obviously" knew Mohammed Sidique Khan well.

"I genuinely believe that they could have prevented July 7," he said.

"The Government failed us on that day, they failed the entire country and they did not tell the truth - that is what gets to me."