A report's due to be released about how MI5 and the Police handled intelligence ahead of the terror attacks in Manchester and London this summer.
The Anderson Report is expected to recommend how the security services can minimise the chances of missing potential attackers in the future.
Following attacks at Westminster, Manchester, London Bridge, and Finsbury Park, MI5 and the police launched internal reviews to:
- Consider what was known about the perpetrators prior to the attacks;
- Examine decisions made regarding any intelligence held before the attacks took place;
- Identify areas for improvement, such as in the management of thousands of individuals who have been looked at as part of previous inquiries but who are not currently under active investigation.
The assessments have been carried out internally but David Anderson QC was appointed by the Government to provide "independent assurance"
It emerged that perpetrators of the Westminster and Manchester atrocities, as well as one of the London Bridge attackers, had at some point been on the radar of authorities - although none was considered high risk at the time of the attacks.
In a speech in October, the head of MI5 Andrew Parker said that when an attack happens "we are determined, using the harsh light of hindsight, to squeeze out every last drop of learning so that we can be the very best we can be, now and in the future."
The scale of the current threat is seen as unprecedented.
Counter-terror teams are running about 500 live investigations involving 3,000 individuals at any one time, while there is also a wider pool of 20,000 former "subjects of interest" who must be kept under review.
It is understood police and MI5 have foiled nine plots since March, in addition to the terrorist incidents that have occurred.