MI5 'overstretched' before 2005 bombings

But lawmakers on the Intelligence and Security Committee cleared the domestic security service, MI5, and Special Branch police officers of failing to link Mohammed Sidique Khan to the plot that left 52 people dead.

The report, which was heavily censored for security reasons, said lawmakers "cannot criticise" decisions made by investigators despite the fact Khan came to their attention several times.

Lawmakers said it had been correct for officers not to dig further into his background despite observing him meeting extremist plotters because there was no evidence at that stage that he posed a threat to national security.

The report reveals that a police surveillance unit filmed Khan in 2001 as part of an operation to track suspected extremists.

However, he was not identified from the images and his significance was only realised after the suicide bombings.