More than 250 survivors of the Manchester Arena bomb are taking legal action against MI5, lawyers representing them have confirmed.
Twenty-two people died and hundreds more were injured in the blast in May 2017.
Legal teams representing many survivors injured in the explosion said they have submitted a group claim to the Investigatory Powers Tribunal (IPT).
MI5 said it would not comment on ongoing legal proceedings.
In March 2023, the director-general of MI5 Ken McCallum said he was "profoundly sorry" the security service did not prevent the Manchester Arena attack.
His comments followed the findings of a public inquiry which concluded MI5 missed a significant chance to take action that might have stopped the bombing.
Chairman of the inquiry Sir John Saunders said the intelligence could have led to suicide bomber Salman Abedi being followed to a car where he stored his explosives.
Mr McCallum said he regretted that such intelligence was not obtained.
He said: "Gathering covert intelligence is difficult but had we managed to seize the slim chance we had, those impacted might not have experienced such appalling loss and trauma."
Hudgell Solicitors, Slater & Gordon and Broudie Jackson Canter are the three lead firms in the action now being brought against MI5.
In a joint statement, they confirmed they had collectively submitted a group claim on behalf of more than 250 clients to the IPT.
"As it is an ongoing legal matter, we are unable to provide any further details, or comment further, at this stage," they said.
The IPT is an independent judicial body which provides the right of redress to anyone who believes they have been the victim of unlawful action by a public authority using covert investigative techniques.
It also consider complaints about conduct by, or on behalf of, the UK intelligence services.
