Victims of the London bombings have handed in a letter to the Home Secretary demanding a public inquiry after learning that MI5 had been aware of at least two of the 7/7 London attackers.

It emerged yesterday that Mohammad Sidique Khan, the leader of the 7/7 bombers, had come under surveillance because of his closeness to the gang of young British Muslims convicted yesterday of plotting to explode a massive fertiliser bomb at a nightclub or shopping centre.

In 2003, Khan attended a terror training camp in Pakistan with some of the fertiliser plotters. Back in Britain, agents of MI5, the Security Service, had seen Khan meeting the fertiliser bomb plotters on five occasions in 2004, and had gone so far as following his car, it was revealed. Surveillance tapes included recordings of Khan talking about terrorism with Omar Khyam, the leader of the fertiliser bomb plot.

Shehzad Tanweer, the deputy leader of the London bombers, and Khan had both been photographed with Khyam. In addition The Times has learnt that an alleged al-Qaeda financier was known to have rung a mobile phone owned by a "Sidique Khan".

Until yesterday, the Government had insisted that the 7/7 attacks could not have been predicted or prevented because the bombers were "clean skins" - that is, unknown to the security services.

The revelation that this was far from the truth today prompted a group of those injured or bereaved in the London attacks to deliver a letter in person to John Reid, the Home Secretary, calling for a comprehensive, accurate and definitive account of what happened.

The group spoke of the colossal impact of the four bombs that exploded on July 7 2005, three on underground trains and one on a bus.

"Fifty-two families have lost their loved ones. Each person murdered leaves a devastating trail of loss," the group said, in a statement read aloud outside the Home Office this morning.

"Nearly 800 people have been injured. Many remain permanently disabled. Thousands of people's lives will never be the same again as a result of the first suicidal bombings on Western soil.

"Here we stand, with so many questions still unanswered, driven by the pure desire to save lives by finding out the truth. This is not about blame, but about future public safety, understanding what happened and how to stop it happening again.

"We have come together as a group on account of this terrible event which has touched us personally. We are today formally asking the government for a written response to our request for an independent and impartial public inquiry."

Among the 7/7 Inquiry Group was Rachel North, who survived the blast on the Piccadilly Line train. Ms North, who led today’s lobbying, said yesterday’s revelations had made many people more determined to fight for an inquiry.

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