The Manchester Arena terror attack might have been prevented had MI5 acted on key intelligence received in the months before the attack, an inquiry has found.

Two pieces of information about suicide bomber Salman Abedi were assessed at the time by the security service to not relate to terrorism.

But inquiry chairman Sir John Saunders said having heard from MI5 witnesses at the hearings into the May 2017 atrocity, which killed 22 people and left hundreds injured, he considered that did not present an “accurate picture”.

The officers admitted they considered a possible pressing national security concern on one of the pieces of intelligence but did not discuss it with colleagues straight away and did not write up a report on the same day.

In his 207-page report, Sir John said: “The delay in providing the report led to the missing of an opportunity to take a potentially important investigative action.

“Based on everything the Security Service knew or should have known, I am satisfied that such an investigative action would have been a proportionate and justified step to take. This should have happened."

Richard Scorer, principal lawyer at Slater and Gordon, who represented 11 of the families at the inquiry, provided the following statement.

He said: "It is now very clear that there was a failure to properly assess key intelligence about Salman Abedi; a failure to put it into proper context; and – most catastrophic of all - a delay in acting on it.

"As a result of these failures, at the very least, a real possibility of preventing this attack was lost. This is a devastating conclusion for us.

"On 22 May 2017, thousands of people left their homes to attend a concert at Manchester Arena. Those killed and injured in this murderous attack had every right to feel safe and protected, but as this inquiry has demonstrated, they were failed at every level - before, during and after this horrific attack.

"Even now, some families feel let down by the government’s refusal to allow them to register their loved one’s death, which for some is a key part of the grieving process and which is now wrongly being denied to them."

Mr Scorer said the failures exposed in the report were "unacceptable" and said information of national security importance must be acted on speedily. 

He also thanked Sir John and the inquiry legal team for "for their unwavering determination to uncover the truth" and paid tribute to those who lost their lives.

The families have asked that their privacy is respected as they process the findings.