An unmarried father is to take a case to the High Court in an attempt to have his two-year-old twin sons returned to him in Ireland from England.
They were taken by their mother to Manchester from the couple's home in January.
A leading family law expert said last night that the case had the potential to be "hugely significant" in forcing the Irish courts to make a ruling on the rights of unmarried fathers.
The man, known as Mr G, went to the High Court in London earlier this week to seek custody of the children under the terms of the Hague Convention.
Under the convention, a parent must prove that he or she had a right of custody at the time of a child's removal in order to claim parental responsibility.
In legal submissions made to the court, the mother argued that, because the father did not have guardianship rights under Irish law, she did not require his consent to take the children out of the country, and an English court was the proper forum to decide custody.
However, the father said that, had he been given the opportunity to apply for guardianship rights in Ireland before the children were taken to Britain, he would have got them.
Mrs Justice Mary Hogg said it was not appropriate for her to make a ruling on returning the children to Ireland.
She said that without a formal guardianship agreement or court-appointed order, there existed no binding legal ties between an unmarried father and a child in Ireland. The custody of the children was therefore a matter for the Irish courts and it was not up to a British court to decide on something that was of constitutional importance in Ireland, she said.
The man, who had been the primary carer, sought to argue that he had a right of custody to the children under the European Convention on Human Rights and that the convention made no distinction between married and unmarried families.
Mr G, with the support of the Unmarried Fathers of Ireland group, is now seeking an urgent High Court hearing in Ireland to determine if he has the right to custody of the children. He said he would take the case to the European Court of Human Rights in Strasbourg if that right was not vindicated in the High Court.
Unmarried Fathers of Ireland spokesman Donnacha Murphy said they would look for a High Court date by the end of this week and the case had the potential to become a landmark judgment. "The facts of this case would appear to constitute an ideal case for the consideration of discrimination within Irish family law legislation," he said.
"This case, when it reaches the High Court, will raise constitutional issues that need to be addressed to balance the changes in our society that evolved through the passage of time and the time has come to implement these changes."
