More than 250 survivors of the 2017 Manchester Arena attack have filed a lawsuit against Britain's domestic intelligence services, their lawyers said.
In May 2017, 22 people were killed and 100 injured when suicide bomber Salman Abedi, 22, detonated his device at an Ariana Grande pop concert.
Last year, MI5 director general Ken McCallum expressed "deep regret" intelligence was not gathered that might have stopped Abedi.
An inquiry found the bombing might have been prevented had MI5 acted on intelligence received in the months before the attack.
Two pieces of information about Abedi were assessed at the time by the security service to not relate to terrorism.
But Investigatory Powers Tribunal chairman Sir John Saunders said, having heard from MI5 witnesses at secret hearings, he considered that did not present an "accurate picture".
The suicide attack, as concert-goers were leaving the show at the Manchester Arena in northern England, was carried out by Abedi, 22, who was from Manchester but of Libyan descent.
Inspired by ISIS, he used a homemade shrapnel bomb against crowds of mostly young people who had been attending the concert by the US pop star, and parents who had come to pick up their children.
The IPT is an independent body that investigates complaints from people who believe they have been victims of unlawful action by a public authority using covert investigative techniques, and those against the intelligence services.
Delays in relation to one of two pieces of intelligence led to the "missing of an opportunity to take a potentially important investigative action", Sir John, the chairman of the 2023 enquiry, said in his report last year.
“Legal teams representing injured survivors of the Manchester Arena bombing in 2017 can confirm that they have collectively submitted a group claim on behalf of more than 250 clients to the Investigatory Powers Tribunal,” a statement on behalf of Hudgell Solicitors, Slater and Gordon and Broudie Jackson Canter said.
“As it is an ongoing legal matter, we are unable to provide any further details, or comment further, at this stage.”
The three firms are representing the injured survivors’ group.
Manchester bombing — in pictures
MI5 said it would not comment on continuing legal proceedings.
The IPT was established under Section 65 of the Regulation of Investigatory Powers Act 2000.
The tribunal considers complaints under the Ripa and claims under the Human Rights Act 1998.
It considers allegations of unlawful intrusion by public bodies, including the UK intelligence services, the police and local authorities.
It investigates alleged conduct by or on behalf of the UK intelligence services, whether or not it involves investigatory powers.
Who is Salman Abedi?
Abedi was born in Manchester in 1994 and grew up in a family with strong ties to Libya.
He visited Libya during the civil war there and was believed to have received training or help in building a bomb while he was there.
His father, Ramadan Abedi, had made clear on Facebook his support for suicide attacks in the Libya conflict.
Salman and his brother Hashem Abedi were rescued from Libya by the Royal Navy in 2014.
Before the suicide bombing, Salman Abedi was known to security services but was not considered an imminent threat.
He died in the explosion at the arena.
