But Mr Masson’s lawyers argued that, under the Commonwealth law, Mr Masson should be the parent, as he is the biological father and was involved in the child’s life.

Mr Masson had donated his genetic material in 2006 in a private, personal insemination to his friend of about 25 years, named under a pseudonym as Susan Parsons.

Mr Masson agreed on the understanding he would help as a parent, provide financial support and physical care.

He is named as the girl’s father on her birth certificate.

Issues arose when the mother and her partner, Margaret, tried to take the girls, then aged 10 and 9, to live in New Zealand, where the couple married in 2015.

Mr Masson was at first successful in fighting their move overseas, but the Parsons appealed before a full court of the Family Court, which agreed with the women that he was not a legal parent.

They successfully argued that the laws in most of the states rule out a sperm donor from being a father and that Mr Masson was therefore not a parent.

He argued that the Commonwealth law should apply, and said the question of who is a parent should be determined by the circumstances of each case, with reference not only to who provided the genetic material but also who had participated in social and psychological parenting of the child.

His position was backed by Commonwealth Attorney-General Stephen Donaghue, QC, and the independent children’s lawyer.

The term “parent” should take its ordinary and contemporary meaning, they argued.

Mr Masson’s lawyers said that, as he had had considerable involvement in the child’s upbringing, including volunteering at the school canteen, he was not simply a sperm donor but the father.

With AAP, Alexandra Back