What happened in this case?

About two years ago, two couples - one white and one black - underwent IVF treatment at the Assisted Conception Unit at Leeds General Infirmary.

The white woman became pregnant and gave birth to mixed race twins. Genetic tests established she was their biological mother, which meant doctors had used the correct egg.

However, tests also revealed the woman's eggs had not been fertilised with her husband's sperm as planned.

An internal hospital inquiry suggested the mistake probably occurred either when the samples of sperm were placed in a centrifuge or when they were removed from a storage box immediately before being injected.

Why did the case end up before the High Court?

This case ended up before the High Court so that the biological and legal parentage of the twins can be sorted out.

This will determine which couple will have the right to bring up the children and whether the other couple will have any rights to see the twins.

What has the court decided?

Late last year, Dame Elizabeth Butler Sloss declared that the black man, referred to as Mr B for legal reasons, is the biological father of the twins.

DNA tests showed his sperm had been used to fertilise the white woman's eggs. She cannot be named and is known only as Mrs A.

Dame Elizabeth has now decided that Mr B is also the twin's legal father. This means that potentially he will have certain rights over the children if he seeks them.

It also means that Mr A, the white woman's husband, will have to adopt the children if he wishes to be recognised as their legal father.

How did the court come to this decision?

Dame Elizabeth had to consider this case in respect of the Human Fertilisation and Embryology Act 1990.

Section 28 of this Act states that the legal father of a child born by assisted conception is the husband of the biological mother unless he does not give his consent.

Legal argument in this case has centred on whether Mr A gave his consent. Lawyers had argued that he is not the legal father because he only gave his consent for his wife to be impregnated with his sperm and not Mr B's or anyone else's sperm.

There has been no similar case in British legal history. Dame Elizabeth's ruling is a landmark decision.

What are the implications for other couples?

Thankfully, IVF mix-ups are rare in Britain. However, this case sets a precedent in the event of a similar blunder in the future.

Dame Elizabeth's ruling would suggest that legal parentage of children born as a result of an IVF blunder will be awarded to the biological parents.

Could this mix-up happen again?

The Human Fertilisation and Embryology Authority which regulates IVF treatment insists this is a unique case.

Last year, it tightened up procedures at clinics. All centres licensed to offer IVF treatment were told they had to double check the identification of people undergoing treatment and the sperm and eggs at the time of insemination.

They also were told to double check the identity of the embryo and patient during embryo transfer and the gametes and embryos at the time of freezing and thawing.