The Manchester terror attack which killed 22 people may have been avoided if MI5 had made different decisions, an official report has revealed.
The wide-ranging report covered the recent terror attacks in Westminster, Manchester, Finsbury Park and London Bridge, which killed a total of 36 people.
And three of the six attackers were on MI5’s radar, the report stated.
The Westminster attacker Khalid Masood had previously been a person of interest but, like Abedi, was no longer under investigation.
Mr Anderson said in retrospect different decisions might have been taken, but it was unknowable whether Abedi would then have been stopped.
His report raised questions for M15 and police as they continue to battle the threat of terrorism.
The report added the intelligence regarding Abedi was linked to criminality, possibly gang activity, rather than terrorism.
Mr Anderson said: “With the benefit of hindsight, intelligence was misinterpreted in 2017.”
An independent assessment by Mr Anderson QC concludes that there is “no cause for despair”, saying most attacks continue to be successfully disrupted.
But he notes that, other than in the case of Finsbury Park, it cannot be said that MI5 and police were “entirely blindsided”.
“Substantial and appropriate coverage was in place around key individuals, and mechanisms designed to assess risk were working as intended.
“MI5 and counter-terrorism policing got a great deal right; particularly in the case of Manchester, they could have succeeded had the cards fallen differently.”
Home Secretary Amber Rudd said in a Commons statement the blame for the attacks lay with those “whose cowardly acts killed 36 innocent people this year and those who encouraged them”.
Ms Rudd said: “In early 2017, MI5 nonetheless received intelligence on him, which was assessed as not being related to terrorism. In retrospect the intelligence can be seen to be highly relevant. Had an investigation been reopened at the time, it cannot be known whether Abedi’s plans could have been stopped. MI5 assesses that it would have been unlikely.”
The Home Secretary also revealed MI5 and counter-terrorism police were currently running “well over” 500 live operations – a rise of a third since the start of the year – involving about 3,000 “subjects of interest”.
Ms Rudd also revealed there are over 20,000 further individuals who had been previously investigated “and may again pose a threat”.
She said nine terror attacks had been prevented in the UK since the Westminster attack in March.
The Met Police said the number of dangerous, radicalised individuals was “a major issue”.
Commissioner Cressida Dick said her force needed “to make rapid progress in implementing the recommendations, many of which require new technology, better infrastructures and resources”.