Read the story of a British Muslim who survived the 7/7 bombings

A parliamentary investigation panel with access to highly-classified material has cleared the police and intelligence services of any serious lapses in the run-up to the July 7 bombings in London, according to a leaked report.

But the Intelligence and Security Committee, a cross-party panel of MPs that reports to the Prime Minister, expressed concern that Mohammad Sidique Khan, the leader of the bombers, was not properly investigated despite being known to police.

MI5 had Khan and Shehzad Tanweer, another of the four suicide bombers, under partial surveillance for a year before the attacks that killed 52 people. Neither was judged a serious enough threat to justify a comprehensive surveillance operation.

Khan, 30, blew himself up in a train near Edgware Road station and killed seven people. Tanweer, who was 22, detonated a bomb in his rucksack at Aldgate and killed eight.

According to a leak of the report obtained by the BBC, the committee also questioned the general quality of intelligence about the activities of British extremists in Pakistan.

Khan travelled to northern Pakistan in late 2003. He returned with Tanweer in November 2004. Little is known about their visits although Khan is believed to have learned how to use explosives at a terrorist training camp.

The BBC reported that the committee, chaired by Paul Murphy, the former Northern Ireland Secretary, also criticised Britain's terror alert system for being unclear and difficult to understand.

The national threat level was lowered from "severe, general" to "substantial" just before the bombings. Although the MPs decided that the change in status had no effect on the ability of the police to prevent the attacks, they said that the system should be modified to be more easily understood by the public.

The Intelligence and Security Committee has questioned dozens of police and security officers, including Dame Eliza Manningham Buller, the Director-General of MI5, to prepare its report, which it is expected to deliver to the Prime Minister next month. An edited version will then be made public.

The investigation has run alongside the Home Office's compilation of an official "narrative" of the attacks.

Last year, Charles Clarke, the Home Secretary, ruled out a public inquiry into the July 7 bombings, saying that the atrocity was still under police investigation and that information gathered after the attacks was expected to be used in upcoming court cases.

David Davis, the Shadow Home Secretary, said today's leaked details were sufficient to show that the Government should now order a larger inquiry into the bombings.

"This raises serious questions about the monitoring of terror suspects," he said. "The Government should now answer our call for an independent inquiry so that the lessons of the July bombings can be learnt."

"This report also reinforces our call for a clearly understandable and public system of alert and threat levels, like they have in America."

Nick Clegg, the Liberal Democrat home affairs spokesman, said report appeared to be "a helpful guide for improvements in our internal security arrangements which we can only hope will be adopted by the security services."

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