Two young sisters were taken away from their biological mother and handed over to her former lesbian partner on the orders of a court yesterday.

The mother, a teacher, had defied the orders of a judge by secretly taking the children to a new home in Cornwall after the Court of Appeal granted her former partner shared contact with the girls aged seven and four.

After she and the children were tracked down, the High Court granted primary care of the children to the former partner and this was confirmed yesterday by the Court of Appeal.

Lord Justice Thorpe, who headed the panel of three judges, said in his ruling: "We have moved into a world where norms that seemed safe 20 or more years ago no longer run."

He then posed the question: "Who is the natural parent?"

In the past, judges dealing with such cases have held that the biological parent is the natural parent, he said.

"But in the eyes of the child, the natural parent may be a non-biological parent who, by virtue of long settled care, has become the child's psychological parent."

He said that in this case the upbringing of the children had been shared and the sisters would not distinguish between one woman and the other on the grounds of biological relationship.

None of the parties involved in the case can be identified, by order of the court, to protect the children.

The biological mother was referred to as CG and she gave birth to the children, A and B, after insemination by anonymous sperm donation during the relationship with CW.

A and B are full sisters. The relationship broke down in 2002 after seven years and CG moved to a neighbouring house until she found a new lesbian partner in Leicester, said Lord Justice Thorpe.

"That relationship endures and the couple have registered their civil partnership," said the judge.

CW, aged 47, was initially denied access and any parental responsibility by a county court judge in Telford, Shrop-shire, but this was overturned by the Court of Appeal in April last year.

The panel of judges, again headed by Lord Justice Thorpe, ruled that same-sex partners should have the same rights as estranged heterosexual couples.

CW was awarded joint residency rights after the judges said that shared responsibility would be "vital" for the children's psychological health.

A condition that CG should not take the children to Cornwall remained in place after that appeal ruling which the mother said was "an appalling decision made in an afternoon", said Lord Justice Thorpe.

Requests to CW's solicitors for consent to move to Cornwall were refused but CG put her house in Leicester up for sale and registered the children at a school in Cornwall.

While the children spent their summer holidays with CW and her new partner, CG and her partner completed the sale of the house in Leicester and bought a house in Cornwall.

"This, of course, was a flagrant breach of the court's control of the arrangements for the children and an elaborate deception of CW," said Lord Justice Thorpe.

To maintain the deception, CG returned to Leicester to pick up the children at the regular handover point and then drove through the night to Cornwall.

When CW realised the children were missing, she contacted the mother's solicitors who told her that CG had been forced to make the decision against the court's orders in the interests of the child, said Lord Justice Thorpe.

In February this year, Mrs Justice Bracewell heard the case in private at the High Court Family Division and allowed CW to take over as primary carer of the children.

CG took the case to the Court of Appeal, where Lord Justice Thorpe said the child's views on which partner is the psychological parent should be taken into consideration when deciding on the competing claims of same sex unions.