Taoiseach Leo Varadkar has told the Dáil that excavation of the Bon Secours Mother and Baby Home in Tuam will require new legislation, which will not be ready until the first quarter of next year.

Yesterday the Government approved the forensic excavation of the site.

Significant quantities of human remains were discovered there last year. 

The Mother and Baby Homes Commission of Investigation began test excavations at the site of the children's burial ground at the Dublin Road housing estate in Tuam in October 2016.

The commission was established following allegations about the deaths of 800 babies in Tuam over a number of decades and the manner in which they were buried.

The commission said significant quantities of human remains were discovered in at least 17 of 20 underground chambers that were examined last year.

The mother-and-baby home was operated by the Bon Secours Sisters from 1925 to 1961.

Today Mr Varadkar acknowledged that the Government is "honestly not sure what we are getting into" as a mass grave has never been excavated in this way before in Ireland.

Responding to Sinn Féin Leader Mary Lou McDonald during Leaders' Questions, he said: "We are going to do it on a phased basis, as we are honestly not sure what we are getting into. But we do know that it is the right thing to do."

He said that a mass grave has never been excavated before in Ireland so "we require new primary legislation and bespoke legislation. We expect to have that in the first quarter of next year." 

Ms McDonald said it is two years since a significant quantity of human remains were discovered after they were "unceremoniously buried" at the home and added that "it is a cause of national shame".

She commended Minister for Children Katherine Zappone and the Government for yesterday's decision to excavate the site.

She also praised the work of local historian Catherine Corless, who uncovered the burials at the Tuam site.

It is more than five years since the local historian discovered official records showing that 798 infants and children had died at the site of the mother-and-baby home in Tuam.

Ms Corless believed that most of them were buried on the Tuam site, which is now partly covered by local authority housing and a playground.

Today Ms McDonald asked what legislation is required before the excavation can begin and when it will be debated in the Dáil.

She said the cost of the forensic excavation has been estimated to be between €6m-€12m and asked where that estimation came from.

Ms McDonald said the Order of Bon Secours should pay significantly more that €2.5m pledged yesterday.

She said she hopes yesterday's decision is the start of a process to investigate and locate bodies in other mother-and-baby home sites.

The Taoiseach also praised the painstaking research of Ms Corless. He detailed that there will be a phased approach to the forensic excavation and recovery of the juvenile human remains in so far as is possible.

He said: "If we stumbled across a mass grave tomorrow we would carry out an investigation and that is what we are doing. But we are going to do it on a phased basis as we are honestly not sure what we are getting into. But we do know that it is the right thing to do."

He said that this a mass grave has never been excavated before in Ireland so "we require new primary legislation and bespoke legislation. We expect to have that in the first quarter of next year." 

He said the estimate from the Department of Children and Youth Affairs is that this will cost between €6m and €12m but he acknowledged that as this was not done before it is difficult to know the cost. 

Ms McDonald stressed that "Tuam is not unique" and people speculate about other sites. She added: ""This is unchartered territory for us but we need to get it right."