A detailed report into the 7 July 2005 bomb attacks on London has been published by the Parliamentary Intelligence and Security Committee. The main findings are set out below.
WHAT WAS KNOWN BEFORE THE ATTACKS?
No UK security agency reported any prior warning of the attacks from any source, including from foreign intelligence services, and none of the bombers had been identified - "that is, named and listed" - as potential terrorist threats.
Prior to the 7 July attacks, MI5 had come across Sidique Khan and fellow bomber Shehzad Tanweer "on the peripheries" of other surveillance and investigative operations.
But their identities were then unknown and there was no appreciation of their subsequent significance.
With more pressing priorities at the time, including the need to disrupt "known plans" to attack the UK, it was decided not to investigate the two men further.
A series of further investigative attempts were made, as resources became available, but these resources were soon diverted back to what were considered to be higher investigative priorities.
Tanweer and Khan had come to security services' attention
Khan was also the subject of reporting to the security services from "detainees" outside the UK, but his true identity was not revealed until
after the 7 July attacks.
The failure to show a photograph of Khan to these detainees before the attacks was a "missed opportunity", although there is no guarantee that he would have been identified this way, nor that had he been identified significantly greater resources would have been put into pursuing him.
The chances of identifying plans for the 7 July attacks and preventing them "might have been greater" had the security service taken "different investigative decisions" in 2003-2005.
But, "in light of the other priority investigations being conducted and the limitations on security service [MI5] resources, the decisions not to give greater investigative priority to these two individuals were understandable".
MI5 also found in their records after the attacks a telephone number which it was only possible to identify in hindsight had belonged to another of the bombers, Germaine Lindsay.
The explosions were caused by home-made organic peroxide-based devices, a substance which is dangerous to manufacture but does not require a great deal of expertise.
The bus bomber, Hasib Mir Hussain, stopped to buy batteries before his device exploded - an hour after the others. "It is possible that this indicates he had difficulty setting off his device."
There is "no apparent significance in the choice of 7 July as the date for the attacks" and no indication that the G8 conference taking place at Gleneagles at the time was a factor.
The group "was in contact with others involved in extremism in the UK". But there is no intelligence to indicate that there was a fifth or further bombers.
Claims that a "mastermind" left the UK the day before the attacks "reflect one strand of an investigation that was subsequently discounted by the intelligence and security agencies".
Khan visited Pakistan in 2003 and spent several months there with Tanweer between November 2004 and February 2005, during which time it is thought "likely" they had "some form of operational training" and "had some contact with al-Qaeda figures".
However, the extent to which the attacks were externally planned, directed or controlled by contacts in Pakistan or elsewhere remains unclear, as does the degree of al-Qaeda involvement both in terms of support and control, although this is still under investigation.
THREAT LEVEL & ALERT STATE SYSTEMS
It was "not unreasonable" to reduce the threat level to the UK in May 2005 from "severe general" to "substantial", and the reduction was "unlikely" to have affected the chances of preventing the 7 July attacks.
UK'S ALERT SYSTEM
Current system introduced June 2003
Seven threat levels used: negligible; low; moderate; substantial; severe (general); severe (defined); critical
Threat level set by Joint Terrorism Analysis Centre (JTAC)
Full threat level reports are highly classified as they include details such as intelligence sources
Summaries with fewer details are produced, although still on 'restricted' basis, for wider circulation
However, an alert system in which changes have "little or no practical effect" should be overhauled.
A new system should make clear the limitations of intelligence coverage and the possibility of attack planning going on without detection to help avoid "inappropriate reassurance" about the threat level. This will help ensure security organisations have all the relevant information to make necessary decisions.
There should be greater transparency in the threat level and alert state systems, "more thought" given to what the public is told, and clarity between the various systems and levels.
ASSESSING THE THREAT
The attempt by Richard Reid, the British 'shoe bomber', to blow up a transatlantic flight in 2001 "clearly illustrated the possibility of British nationals becoming involved in terrorist activity".
But intelligence reports in 2002 revealed it was thought an attack within the UK would be more likely to come from terrorists entering the country from abroad.
By 2004 this view, and the threat itself, had changed: "Security Service investigations and successful disruptions in the UK revealed that British-born citizens were involved in plotting attacks on their home soil."
After 9/11, it was thought that key government and "iconic" buildings would be top targets for Islamist terror groups.
However, by 2003, it was felt that "soft targets" including transport networks and shopping centres were the most likely targets, a view reinforced by the Madrid train bombings in March 2004.
A report by JTAC [Joint Terrorism Analysis Centre, responsible for analysing and assessing international terrorism] in May 2005 identified the UK rail networks as high on the list of possible terrorist targets, especially those which were "high profile or iconic".
However there was no intelligence to suggest attacks were currently being planned on the railways or the London Underground.
It was judged that suicide attacks would not become the norm in Europe in a March 2005 assessment by the JIC [Joint Intelligence Committee, which briefs ministers on assessments from all the main UK intelligence agencies].
However, after the case of Richard Reid and two Britons who had travelled to Israel to carry out suicide bomb attacks in Tel Aviv, there were "clearly grounds for concern" that some UK citizens might engage in suicide attacks, and the JIC judgement could have had an impact on the alertness of the authorities and their ability to respond.
The security services 'need to work with overseas agencies'
Across the whole counter-terrorism community the development of a home-grown threat and radicalisation of British citizens were "not fully understood or applied to strategic thinking".
A better level of understanding in MI5, the police, and the government is "critical" to prevent future attacks.
Briefings prepared by the JIC and JTAC should more systematically include assessments of the "level of visibility" of a threat, and the limits of intelligence on the threat.
This would avoid oversimplification of the threat to the UK and the potential for giving inappropriate reassurance about the threat.
The need to address the limitations of intelligence in intelligence assessments was raised by the Butler Review, but there is concern that this has not yet been fully implemented.
Three terrorist plots in the UK have been thwarted by the intelligence and security agencies since July 2005.
RESOURCES AND COOPERATION
National standards for counter-terrorism need to be improved. Plans to merge police forces should not remove policing from its local roots and undermine knowledge at a local level.
More needs to be done to improve joint security service and special branch efforts on the "home-grown" threat.
Recent efforts to bring about improvements in the services show that more could have been done to bring about change before the attacks.
Efforts to improve cooperation with intelligence services abroad must also "be at the heart of future efforts" to beat international terrorism.
"Greater coverage in Pakistan, or more resources generally in the UK, might
have alerted the [security] agencies to the intentions of the 7 July group."
It "seems highly unlikely that it will be possible to stop all attacks", even with more "intrusive" intelligence services.
At present there is not a group with both the current intent and the capability to attack the UK.
Any threat is as likely to come from those who appear well assimilated into mainstream UK society, with jobs and young families, as from those
within socially or economically deprived sections of the community.