An independent report commissioned by the Government on the practice of illegal adoptions in Ireland has recommended the establishment of a State inquiry.

The report, by Prof Conor O'Mahony, the Government's Special Rapporteur on Child Protection, also advises that those affected by illegal birth registrations should receive a State apology.

Last year, following an RTÉ investigation that examined how thousands of Irish babies were illegally adopted over several decades, the Government commissioned the report to advise on next steps.

The affected adoptees, all of whom are now adults, were registered at birth as if they were the biological children of their adoptive parents.

Following the publication of the 38-page report, the Government on Monday said it would offer those affected an apology in Dáil Eireann during the advancement of the upcoming Birth Information and Tracing Bill.

Minister for Children Roderic O'Gorman also said the Government would make once-off payments of €3,000 to affected individuals.

This payment, which will be given only to individuals whose illegal adoptions were facilitated by St Patrick's Guild, will represent a contribution towards costs associated with, for example, DNA testing and legal fees.

The Government stopped short of committing to the establishment of a State inquiry, saying it will "need to give further consideration to this specific recommendation".

It noted, however, that Mr O'Gorman had begun initial work to create a process for survivors of Mother and Baby and County Home Institutions to share their experiences as part of an official record.

Speaking on RTÉ's Drivetime, Prof O'Mahony said that his report recommends the establishment of an inquiry that follows the truth commission model, rather than a commission of investigation.

"The truth commission model is less focused on trying to name names and accountability and more focused on establishing an accurate narrative," he said.

Prof O'Mahony's report concluded the State was aware of the criminal offence of illegal birth registrations for many decades. Successive governments, it finds, repeatedly failed to adequately remedy these human rights violations.

It adds that inaction has exacerbated the impact on affected individuals and denied many the opportunity to connect with biological family members.

Speaking on Drivetime, Prof O'Mahony said the practice of illegal adoptions in Ireland had "been an open secret for an awfully long time".

"It's only really in the last few years that we’ve started to see any kind of action to try and identify how many of these cases have happened, who are the people affected, and to try and reconstruct their identities for them," he said.

Some 17 recommendations are featured in the report. They include the need for the State to correct the birth register and enact its proposed adoption-tracing legislation to allow full and unqualified access to personal information as a matter of urgency.

It also calls for the Government to acquire and centralise all adoption files in one location, including files that are currently in private ownership.

This should be followed by a targeted investigation to determine the scale of illegal adoptions here and to inform those affected.

This work, Prof O’Mahony recommends, should be performed by a newly formed specialist tracing team and should be completed as effectively and efficiently as possible.

To fail to do so, he says, would be indefensible and means the true figure of those affected by the practice of illegal registration in Ireland would never be known.

In response to Prof O’Mahony’s recommendations, Mr O'Gorman said that the upcoming Birth Information and Tracing Bill 2022 will "robustly fulfil the vast majority of the recommendations".

In a statement, Mr O'Gorman said that he welcomed the report, noting that progression of the bill was a "priority" for him as minister.

He added: "I will now further develop the Bill to take account of key recommendations made by the Special Rapporteur, such as the specialist tracing service to undertake an additional review of files."

Ivana Bacik, Labour's spokesperson for children, said that she hoped today's report would be "a catalyst for progress for all those who suffered injustice as a result of unscrupulous adoption practices".

She called for a state inquiry and said those affected should be provided with "adequate resources".

Kathleen Funchion, Sinn Féin's spokesperson for children, called "an insult" the decision to make a €3,000 once-off payment to some of those affected.

"This, accompanied by the deeply flawed Birth Information and Tracing Legislation currently before the Children’s Committee, is for many another disappointing blow, and all too familiar for many survivors," she said.

Watch RTÉ Investigates: Illegal Adoptions – Still Searching on Wednesday at 9:35pm on RTÉ One and RTÉ Player.