A cross-party committee of MPs investigating the intelligence failure to stop the London bombings of July 2005 has blamed it on a lack of resources, rather than on any error of judgement.
For the past few months the Parliamentary Intelligence and Security Committee, the ISC, has been interviewing members of the police and intelligence agencies to establish what information they had on the terrorist threat to Britain and how they acted on it prior to 7 July.
MPs say the public should be better informed of terrorist threats
The committee's report, which is being handed to the prime minister's office and which will likely be published at the end of April, essentially addresses the question - could more have been done to stop the bombers getting through?
The conclusion is that while there was clearly a failure of intelligence, no single agency or individual was to blame, given the resources they had.
The committee has questioned why Mohammad Sidique Khan, the lead bomber who killed six people when he blew himself up at Edgware Road Tube station on 7 July, was known to the intelligence services before July but not fully investigated.
The MPs have accepted the official explanation that Khan was suspected of petty fraud not terrorism, so he was not considered a high priority.
Whitehall officials have admitted that they had eavesdropped on telephone conversations made by Khan but that he was not the focus of their investigation, which was centred on an imminent terrorist plot involving others.
It will take years before new [intelligence] recruits are vetted and trained - time which would-be terrorists are expected to exploit
They say no intelligence came to light to suggest Khan was plotting an attack.
But intelligence expert Professor Anthony Glees of Brunel University believes MI5, the security service, should have done more.
He told BBC News: "The security service understands that it is the body that is charged with having good predictive intelligence and what the London attacks show is that there was no good predictive intelligence.
"They didn't look carefully enough at the sort of people who might be tempted into becoming terrorists."
The ISC committee has made a number of criticisms.
Its members are concerned that intelligence-gathering on British militants travelling to Pakistan was not as good as it should have been.
Khan and other members of his cell are thought to have linked up there with extremist radicals, possibly al-Qaeda recruiters.
However, the committee believes it was only after the London bombings that British investigators got full co-operation from their counterparts in Pakistani intelligence.
Another criticism made by the ISC committee is over the complexity, secrecy and ineffectiveness of the present system of threat levels and alert states.
These are raised and lowered in secret according to an intricate sliding scale of terrorist threats.
The ISC believes the system needs to be simplified and the public kept better informed.
Whitehall officials have told the BBC they are now facing an unprecedented number of terrorist plots in Britain.
They say the threat of home-grown terrorism has increased substantially since the Iraq invasion of 2003, and that 50% of recent disrupted plots are home-grown, involving British nationals living in Britain.
Whitehall officials have also said that in practice, counter-terrorism in this age means stopping most but not necessarily all attacks.
The intelligence services are currently undergoing a major expansion with the aim of doubling in size to around 3,000 members each, but it will take years before new recruits are vetted and trained - time which would-be terrorists are expected to exploit.