The Omagh bomb inquiry must uncover “uncomfortable truths” to help prevent future disasters, the father of one of the 29 people killed in the blast has said.

Michael Gallagher, whose son Aiden was killed in the atrocity, described it as the “single worst failure of security and intelligence in the history of this state” ahead of the inquiry’s first public hearing this week.

Mr Gallagher and other bereaved families have spent more than two decades campaigning for an inquiry into the dissident republican bomb which devastated the Co Tyrone town on August 15, 1998, killing 29 people, including a woman pregnant with twins.

He said the inquiry has been an “unbelievably long time coming”.

The inquiry will hear opening statements from chair Lord Turnbull and his counsel Paul Greaney KC during a sitting at the Strule Arts Centre in Omagh on Tuesday.

Mr Gallagher said it will be the first time since 1998 that all of the bereaved families, including those caught up in the blast from Spain, will come together.

The inquiry, ordered by former Northern Ireland secretary Chris Heaton-Harris last year, is examining alleged security failings that led a High Court judge to conclude the outrage could plausibly have been prevented.

It was ordered in response to a court judgment that directed the Government to establish some form of investigation.

In his 2021 judgment, Mr Justice Horner directly recommended that the UK Government carry out an investigation into alleged security failings in the lead-up to the atrocity.

While having no jurisdiction to order the Irish government to act on the matter, the judge urged authorities there to establish their own probe in light of his findings.

Earlier this month, the Irish Cabinet formally agreed to provide assistance to the inquiry.

Lord Turnbull previously said he was confident the terms of reference would allow him to conduct a “thorough and robust investigation”.

Mr Gallagher took a judicial review of a previous government decision against a public inquiry into the Omagh bomb.

“It ended up 10 years in court challenging the government’s decision, then almost a year before the judge made a judgment and then the Secretary of State ordered the inquiry,” he told the PA news agency.

“I still wake up in the morning and wonder is it true. I’m enormously grateful for the Secretary of State granting a public inquiry, I think it’s hugely important.

“This was the single worst failure of security and intelligence in the history of this state, and we had 31 people died and over 250 injured.

“I think it is important that what happened in the lead up to and on the day is examined carefully to see what happened. I’m sure there were things done well and things that could have been done better.

“I feel that that’s the least we owe to the victims, to learn those lessons and pass it on so that others will benefit. Hopefully it will not be an explosion, it could be a train crash and plane crash or a chemical spill, but whatever the emergency, we would be in better shape to deal with that.”

Commemorative and personal statements are set to be made during inquiry hearings next January.

Mr Gallagher said he expects those to be “extremely difficult and painful”.

“Those will take statistics and turn them into real people. It encompassed everybody from grandmothers and grandfathers to unborn children, and I think that will send a message to people about how important it is that we have answers about what happened in Omagh,” he said

“It will be extremely difficult and painful for those that decide to share publicly their experience – after the bomb, that was one of the only things that people felt they had left, their privacy. But I think now is the time to go out and put a face to that statistic. It was a real person affected, and their family, friends and wider family circle.”