The true number of victims of clerical sex abuse within the Dublin archdiocese is likely to number in the thousands — not the 450 cited in a new report drawn up by the Irish Government-appointed Commission of Investigation, it was claimed last night.

“We believe there's a large number of people who were abused in the Dublin diocese who haven't come forward,” the executive director of victims’ group One in Four Maeve Lewis said.

One in Four and other support groups for victims of clerical sex abuse are now urging the Dublin government to delay publication of the report to prepare for the anticipated onslaught of victims who will be coming to terms with its explosive findings. The Commission of Investigation into the handling of clerical sex abuse in the diocese was expected to hand over its long-awaited report to the Republic’s Justice Minister Dermot Ahern yesterday.

However, victims' support groups — including One in Four, The Dublin Rape Crisis Centre and Survivors of Child Abuse (SOCA) — are all urging the minister to hold off on making the findings public until the autumn, when they have sufficient resources in place to cope with the flood of calls they expect the report will generate.

The inquiry was established in 2006 to examine how officials in the Catholic Church and the Irish state responded to widespread allegations of the physical and sexual abuse of children by the clergy between 1975 and 2004.

Archbishop of Dublin Diarmuid Martin has warned that the revelations by some 450 victims will be both “shocking and horrific”.

But independent support groups say they are already inundated with the unprecedented number of victims who came forward since the publication of the Ryan Report into clerical abuse at church-run schools, which was published in May.

Ms Lewis said One in Four has been inundated with 700 new contacts following the Ryan report.

She fears the latest report by Judge Yvonne Murphy will open up the floodgates for victims who have not disclosed their abuse before and will be in need of emergency counselling to cope with the trauma.

“We know that only about 10% of victims come forward, so if Diarmuid Martin is talking about 450 cases it could be closer to 4,500,” she said.

“We've been completely inundated and we're concerned there will be a whole avalanche of new cases.”

She and Ellen O'Malley-Dunlop, chief executive of the Dublin Rape Crisis Centre, have both written to the Irish Justice Minister urging him to delay publishing the report until October.

Ms O'Malley-Dunlop said it is imperative that victims have somewhere to turn once the report is published.

Yet, it also needs to clear up the backlog of new cases generated by the Ryan Report and has requested emergency funding from the government to hire additional counsellors.

In the meantime support groups believe the report will be transparent, but they insist that all perpetrators are named in the report — except for three clergymen who are currently before the Irish courts on child sex abuse charges.

It's believed the report will name 15 paedophile priests, including 11 who have already been convicted of abusing children.

They were among a representative sample of 46 priests who were accused of abusing children since 1975.