A cross-party committee of MPs has concluded that intelligence and security services were not to blame for the 7 July bombings, according to a report.
But the Intelligence and Security Committee will ask the Prime Minister why the lead bomber Mohammed Sidique Khan was not investigated, despite being known to police.
It also questioned the quality of intelligence on the activities of British militants in Pakistan prior to the four suicide bombings on London's transport network, the BBC reported.
The committee is also said to be critical of the system of alert and threat levels which it ruled was unclear.
The national threat level was lowered from "severe, general" to "substantial" just before the attacks that killed 52 people and injured hundreds.
The committee said that although it was probably irrelevant to the bombers' plans, the warning system needed to be simplified for the public.
Khan, 30, was one of the four bombers who took part in the attacks last summer as he detonated explosives in a rucksack on his back near Edgware Road station, killing seven people.
Counter-terrorism officials were said to be aware of Khan, but he was not suspected of being a key player in a radical group.
The report, which will be handed to Tony Blair, was gathered from interviews with the police and intelligence community.Reuse content