White parents gave birth to black twins after an apparent mix-up during their IVF treatment at an NHS fertility clinic, it was reported today.

The error, thought to be the first in Britain, could lead to a court battle over the identity of the twins' legal parents, the Sun newspaper said.

The white couple, who have not been named, went to the fertility clinic for IVF treatment after trying unsuccessfully for years to have a child, it was reported.

During IVF, sperm provided by the father and eggs from the mother are mixed in a laboratory, and are then placed into the mother's uterus to develop.

The mistake could have been caused by the clinic using a black man's sperm to fertilise the white woman's egg, or by the clinic implanting a black couple's fertilised egg into the white woman.

A source at the NHS Trust in question, which cannot be named, told the Sun: "Great steps have been taken to ensure that this sort of thing never happens. It must be a one in a million chance.

"The big problem now is, who are the real parents of the twins?"

IVF, or in vitro fertilisation, is used by about 27,000 couples a year in Britain. Until now, a mistake of this sort has never been discovered.

But in America, Donna Fasano, from New York, gave birth to another couple's baby in 1998. Ms Fasano, who is white, gave birth to a black child and a judge ordered that she should hand the infant over to his biological parents.

In Holland, suspicions were raised when a white woman, Wilma Stuart, gave birth to dark-skinned twins in 1993.

DNA tests showed the hospital had mistakenly mixed sperm from her husband with that of a black man from the Dutch Antilles. She kept the twins.