The couple, referred to by the court as 'David and Eileen Doyle' (not their real names), hired the investigators because they wanted to find out information to damage the natural parents' chances of being re-united with their child. They were particularly looking for evidence that the young couple were not living together and were not suited to looking after the baby.

The details of the hiring of the private detectives and subsequent attempted coverup are contained in the full court judgement, which has been seen by the Sunday Tribune. The judgement also reveals that Ann's natural parents misled the court about details of their efforts to get their daughter back.

The case sprung to national attention last month when Baby Ann was at the centre of a court case over her custody.

Her young natural parents initially said they wanted to put her up for adoption, but subsequently changed their minds before this was finalised.

However, Justice John MacMenamin said Ann could not be given to her natural parents because she had already formed an attachment with her would-be adoptive parents. Previously, the court had only released a summary of the findings, but this newspaper has seen the full judgement which reveals in detail the emotional battle fought by the two couples.

Baby Ann was born in July 2004 and her natural parents . . . given the names 'Catherine and Brian Byrne' by the court to protect Ann's identity . . .

were unmarried students at the time.

They decided that she should be adopted. Four months later, Ann was placed with the Doyles.

In August 2005, the Byrnes, Ann's natural parents, decided they did not want to proceed with the adoption and wrote to the Adoption Board that September seeking to regain custody of their daughter.

MacMenamin, however, decided that baby Ann had established a bond of attachment with the Doyles and ruled that she should remain in their custody.

The landmark judgment is the first time in a tug-of-love would-be adoption that custody of a child has not been given to natural parents.

Until now, Irish courts have always interpreted the constitution as prioritising the rights of natural parents to custody of their children in adoption cases.

In his lengthy judgement, MacMenamin outlined how the Doyles had hired a private investigator to undermine the Byrnes' case.

"It would appear that the purpose of this was to ascertain whether or not the Byrnes were truly living together as man and wife, " the judgement states.

The court also heard how Eileen lied when she was asked about hiring the private investigator.

"When cross-examined on this issue, Mrs Doyle (otherwise Eileen) at first did not tell the truth and denied that a private investigator had been retained, although the following day, while still a witness, she accepted that she had told an untruth and apologised, " the judgement states.

MacMenamin praised the work of the individual social workers involved in the case. However, he criticised the social work and adoption services system for failing to properly support the natural parents at a very difficult time in their lives when they were particularly vulnerable.

"The Byrnes were two young and vulnerable persons trying, in some isolation, to cope with a very human and difficult situationf support was needed from every source. I do not think that they received the support they needed, " the judgement states.

Baby Ann's natural father, Brian, told the court how the huge controversy surrounding international adoptions had helped to convince him that the adoption should not go ahead.

"[The Byrnes] say they became more and more persuaded that the correct place for a child was with its birth parents. Brian stated that a number of media broadcasts on the question of foreign adoptions had an effect on his mind, " the judgement states.

Foreign adoptions became a big story in Ireland last year because of the Tristan Dowse case. Tristan had been adopted in Jakarta by Joe and Lala Dowse and two years later abandoned. His plight received widespread publicity and was the subject of investigations and court cases.

The case highlighted widespread corruption in international adoptions and focused attention on the rights of natural parents in adoption cases.

The Byrnes have appealed the MacMenamin judgment to the Supreme Court.