The Manchester terror attack might have been avoided, had the security services handled some of the intelligence about the bomber differently.
That conclusion is part of an official report into the way in which police and the security services handled intelligence before four terrorist attacks which struck London and Manchester earlier this year.
The assessment by David Anderson QC found that three of the six terrorists involved in those attacks were on the security services’ radar.
Manchester suicide bomber Salman Abedi had twice been a “subject of interest” in MI5 investigations in the years before last May’s attack, but those investigations were later closed and interest in Abedi was downgraded.
However, fresh intelligence was received about the 22-year-old’s activities in the months before the Manchester Arena bombing, but its “significance was not fully appreciated at the time”.
The report concludes that “in retrospect, the intelligence can be seen to have been highly relevant to the planned attack”.
A security services review of intelligence on around 20,000 extremists highlighted Abedi as one of a handful of individuals who warranted “further consideration”.
An MI5 meeting to discuss whether Abedi should be further investigated came too late. It was scheduled for the 31 May, nine days after the bombing.
David Anderson, the former Independent Reviewer of Terrorism Legislation, was asked by the Home Secretary to assess and report on the police and security services’ internal reviews into the attacks.
His report reveals that as well as Abedi, two other terrorists involved in the Westminster and London Bridge attacks were also on the radar of police and intelligence services.
Khalid Masood, who killed five people at Westminster in March, was previously investigated by authorities for extremist links and criminal activity.
However, his active case file was closed five years before the Westminster attack and he was no longer deemed to be a subject of interest.
Khuram Butt, ringleader of the London Bridge attack in June was still actively being investigated by police and the intelligence services, on suspicion of attack planning.
That investigation, Operation Hawthorn, was opened in mid-2015, following information suggesting that he “aspired to conduct an attack in the UK”.
The report said that the authorities continued an active investigation into Butt over a period of two years and “though it continued to varying degrees until the day of the attack, it did not reveal the plans or Khuram Butt and his two co-conspirators”.
Butt, an associate of the jailed radical preacher Anjem Choudary, went on to kill eight innocent people and injure dozens of others in the attack on London Bridge and nearby Borough Market.
He and his two fellow terrorists were shot dead by armed police at the scene of the attack.
In his report, David Anderson stressed the high tempo of counter terror operations.
He said that 22 terrorist plots had been thwarted by the authorities in the past four years, nine in the past year alone.
Mr Anderson said that: “MI5 and the police have identified the need to use data more effectively, to share knowledge more widely, to improve their own collaboration and to assess and investigate terrorist threats on a uniform basis.”
However, he said that “no free society can offer immunity from terrorism, or any other kind of crime”.