Survivors of the July 7 bombings, bereaved relatives and politicians last night demanded an official inquiry into how the Security Service allowed murderous terrorists to slip through its fingers.
They spoke out at the end of Britain's biggest terror trial when it emerged that MI5 had trailed two of the ringleaders of the July 7 plot.
MI5 officers came across Mohammed Sidique Khan and his right-hand man Shehzad Tanweer while investigating another group of plotters who were convicted at the Old Bailey yesterday.
The Security Service dismissed Khan and Tanweer as peripheral figures and failed to fully investigate their activities.
Just 16 months later the terror cell slaughtered 52 people on London's transport network.
The second circle of extremists - led by Omar Khyam, 25, from Sussex - planned to use 1,300lb (600kg) of ammonium nitrate fertiliser for a bomb attack on a busy nightclub or shopping centre.
Khyam and four henchmen were convicted at the end of the massive police investigation, Operation Crevice, and all were jailed for life.
But the end of the year-long, £50m trial was overshadowed by details about links between Khyam and the July 7 bombers.
Rachel North, who survived the blast on the Piccadilly Line train, said: "These men were very much on the radar of the Security Service and could have been stopped, that is going to be very difficult to come to terms with."
Shadow home secretary David Davis said MI5 made a mistake.
Conservatives and Liberal Democrats demanded an inquiry into why the security agencies failed to use intelligence gathered to prevent the 7/7 atrocities and they called on Home Secretary John Reid to explain why the Government said after the 2005 outrages that those involved were not known to the security services.
But Mr Reid yesterday ruled out a public inquiry, saying it would divert the police and security services from the fight against terrorism.
The Old Bailey jury was not told Khyam was a close associate of the leader of the July 7 attacks in order to not prejudice his trial.
The two met at least four times in England while Khyam was under surveillance by MI5.
At one point they were even recorded by Security Service agents talking about terrorism.
Khan and Khyam attended a terror training camp together in Pakistan two years before 7/7 and Khyam also met Shehzad Tanweer - who killed seven people in the Aldgate bomb on July 7 - while under surveillance by MI5.
Yet neither Khan nor Tanweer were classified as priority targets by the Security Service.