The man who discovered the unmarked grave of 800 children has returned to the Tuam site with Irish police – 39 years after his grim discovery.

Local man Frannie Hopkins was just 12 and playing with a friend when they discovered bones in a septic tank at the home run by the Bon Secours order of nuns.

Irish Prime Minister Enda Kenny has ordered a full scale investigation into the Tuam home scandal with as many as 800 children who died between 1921 and 1965 feared buried there.

Police have already begun preparing an initial dossier for Justice Minister Frances Fitzgerald on the unmarked grave at the Catholic Church-run home according to the Irish Independent.

Local detectives Tom Curley and Patrick McHugh visited the site with Hopkins on Friday as a private company scanned the grounds for bones on behalf of another newspaper.

Hopkins outlined to the officers how he and his friend stumbled across the unmarked grave in a disused septic tank.

He said: “They brought me up to the site and I showed them where it was and how we came across it. It was all quite informal and only took about 15 minutes.”

Irish President Michael D Higgins has said he is ‘appalled’ at the reports from Tuam in his native Galway.

The President said: “My first reaction was one of enormous sadness. These are children who while they were alive had rights, the rights to protection, and who, if dead, had the right to be looked after with dignity.

“Time doesn’t remove any of those rights but I think now what is important is that all of the questions that are provoked by this are answered and that they are answered adequately with the assistance of science and forensics.

“I think too there is a reminder in it of history and our past and there is so much to be revealed and there is so much to be learned from these really terrible reports that are appearing.”

Newly appointed Justice Minister Fitzgerald is to fast track the enquiry into the Tuam burial ground discovery.

The Minister said: “There is no doubt that media coverage over the last few days will have inevitably evoked very painful memories.

“A decision on a criminal investigation is an issue for the gardai (police). The purpose of a criminal investigation is to lead to the prosecution of people where the commission of offences had been established.

“Consideration will be given by the Government on how best to proceed in the interests of all those who are affected by these extremely disturbing events.”

In response, Adoption Rights Alliance Susan Lohan has accused the government of lagging behind the church and public opinion in relation to the discovery in Tuam.

She said: “It is inconceivable that anything but a criminal inquiry can be launched into the discovery of the grave.”

Alliance chairman Paul Redmond has also accused the Irish government of dragging its feet on the scandal and told the Irish Independent that he had given the then Children’s Minister Fitzgerald an 8,000-word report on the home but she had failed to take action.

He also revealed that he had held three meetings with Archbishop of Dublin, Diarmaid Martin in 2012.

Amnesty International has also joined calls for an investigation into the deaths at the St Mary’s home in Tuam and said the investigation must consider whether ill-treatment, neglect or other abuses were factors in the deaths.

The Bon Secours Sisters order has welcomed the Government’s announcement of an investigation into what happened at the home in Co Galway, which they ran for 36 years.

In a statement, the Bon Secours Sisters said they were shocked and deeply saddened by recent reports about St Mary’s Home.

The statement also said that when the home was closed all records were returned to the local authority, and would now be held by the Health Service Executive in Galway. They agreed to co-operate with any enquiry.