Sir John Saunders said there was a 'significant missed opportunity to take action' that might have prevented the atrocity, but said it's impossible to conclude whether it would have been.

MI5 failed to share two pieces of intelligence about the Manchester arena bomber with the Counter Terrorism Police North West (CTPNW), one of which could have "led to actions" being taken that prevented the attack.

In the final report into the atrocity, inquiry chairman Sir John Saunders stated that a security service officer should have acted more quickly after receiving information prior to the bombing on May 22, 2017. 

Sir John's finding that there were significant "missed opportunities" to take potentially preventative action was based on evidence given to the inquiry about two pieces of intelligence received prior to the attack.

Witness J, for MI5, confirmed that piece of Intelligence 1 and piece of Intelligence 2 were "assessed to relate not to terrorism but to possible non-nefarious activity or to non-terrorist criminality" on the part of bomber Salman Abedi.

While Sir John said the failure to share the first piece of intelligence is "of concern to me", he does not regard that failure to be causally significant.

He wrote: "It is a further example of a communication breakdown between the Security Service and CTPNW. 

"That said, it was for the Security Service to lead the response to Piece of Intelligence 1."

The inquiry was told that, had this information been received today, it is likely that MI5 would have opened Abedi as a "low-level Lead", which would have prompted minor investigative enquiries.

In terms of piece of intelligence 2, Sir John concluded that this "gave rise to the real possibility of obtaining information that might have led to actions which prevented the Attack".

Witness C - who also first assessed Piece of Intelligence 1 - told the inquiry that after examining the information they considered the possibility that it was "activity of pressing national security concern".

Agreeing with this assessment, Sir John wrote: "Given that Witness C had that in mind, s/he should have discussed it with other Security Service officers straight away. Moreover, s/he should have written the report on the same day, but in fact did not do so."

The delay in providing the report resulted in a missed opportunity to take potentially important investigative action. 

"This should have happened," Sir John wrote.

While impossible to say with "any degree of certainty" what would have happened, he suggested that appropriate action could have led to Abedi being followed to the vehicle which contained the explosive, or being stopped upon his arrival into Manchester Airport on May 18, 2017.

Communication failures between MI5 and counter terrorism policing were a common theme throughout the inquiry.

The report found that these problems appeared to emerge from the systems each used to communicate with the other, adding that both bodies "accepted in their closing statements that there were difficulties with the current systems".

In the conclusions section of his report, Sir John said: "Both organisations work hard to try to prevent terrorists carrying out attacks. Having said all that, if the Security Service or Counter Terrorism Policing make mistakes then these need to be identified and steps taken to put them right."

The chairman makes two recommendations in a closed version of the report which will go to MI5 and counter-terror police; a “gist” of those will be made public at a later date.

Head of Counter Terrorism Policing Matt Jukes said: "I am speaking today alongside the Director General of MI5. Today’s report describes the partnership between MI5 and Counter Terrorism Policing. 

“This relationship is long-standing. It has seen us work side by side to overcome significant threats to the safety and security of the United Kingdom.

“I am sorry that, despite our determined partnership, we did not stop the loss of life, nor the injury and trauma that happened close to here, almost six years ago. 

“Since 2017, we have worked to strengthen our partnership even further. Much of that work goes on in secret but there have been important steps forward.

“New facilities like the world-leading Counter Terrorism Operations Centre demonstrate the progress we have made. We now have better systems and technology to make that happen, but we must maintain that progress.

“We will now respond at pace to the findings made by the Inquiry in both its open and closed reports."

Other findings

Operation Oliban

The report also discussed this CTPNW investigation into the activities of convicted terrorist Abdalraouf Abdallah. who had been in correspondence with Abedi.  

On this, it was agreed by CTPNW and MI5 that the Operation Oliban material relating to Abedi should have been analysed for intelligence by the former's Intelligence Management Unit. 

After conflicting accounts from both bodies, Sir John found on the balance of probabilities that the material was not passed on - likely because of human error.

However, even if this had been done, he said it is "unlikely that it would have made a significant difference to the Security Service’s assessment" of Abedi.

Operation Manteline

Sir John described the investigation into the atrocity - which was led by Detective Chief Superintendent Simon Barraclough - as an "impressive, effective and professional investigation".

The wide-ranging Op resulted in the bomber's brother Hashem Abedi being convicted of 22 counts of murder, attempted murder - encompassing the remaining injured - and conspiring to cause explosions.

Prevent

Sir John found that while Abedi should have been subject to a Prevent referral at some point in 2015 or 2016, "it is very hard to say what would have happened if SA had been approached under Prevent or the Channel programme".