The families of the Manchester Arena bombing victims have been told any mistakes by police or security services will not be covered-up to avoid "embarrassment" at the public inquiry.
Lawyers who are representing loved ones of the 22, called for "maximum exposure" as the inquiry approaches the issue of whether the authorities could or should have prevented the attack.
Inquiry chair Sir John Saunders has already ruled that some evidence and witnesses, if heard in public, could compromise national security.
Those witnesses include counter-terror police officers, a witness for MI5 and an expert witness known as witness Z - a former MI5 officer who will give their opinion on the performance of the security services.
John Cooper QC, representing a number of families, said he did not disagree with the position of closed hearings but called for "maximum disclosure" when possible to ensure national security is not used as a blanket measure to restrict public knowledge of mistakes.
In response, Sir John told the hearing: "The idea I would allow the security service to cover up mistakes in order to avoid embarrassment is something, I can assure you, I would not have done even if I hadn't heard the heart-rending evidence, but I'm even more determined.
"Equally, I would also seek to do everything I could to not disclose things that would result in other people going through the sort of torment that the families in this case have gone through.
"So, that's the balance on both sides, and I can well understand their desire to know absolutely everything they can know, and any mistake that's been made.
"But I know that the last thing any of them would want is for anything to happen in this inquiry which would lead to something like or make it easier for something like this ever to happen again."
The inquiry's hearings on preventability are due to start in November.