The High Court ruling decided legal paternity

The High Court has previously declared that the man, known only as Mr B, is the twins' biological father.

His sperm was mistakenly used to fertilise the eggs of a white woman after a blunder at Leeds General Infirmary.

This latest High Court ruling will potentially give Mr B rights over how the children are brought up.

However, he will not be awarded custody. Dame Elizabeth Butler Sloss, president of the High Court family division, had already declared the twins should continue to live with the white couple, known only as Mr and Mrs A.

The ruling means Mr A will have to adopt the twins if he wishes to become their legal parent.

None of the parties involved in this case can be identified for legal reasons.

Landmark case

This is the first case of its kind in Britain. It is also the first time the courts have been asked to decide on the legal parentage of children born after an IVF blunder.

These two families have gone through an astonishingly traumatic experience Dame Elizabeth Butler Sloss

Giving her ruling, Dame Elizabeth said the twins would remain in a loving home.

"Although they lose the immediate certainty of the irrefutable presumption that Mr A is their legal father, they will remain within a loving, stable and secure home.

"They also retain the great advantage of preserving the reality of their paternal identity."

Under current law, 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.

Legal options

Dame Elizabeth refused Mr and Mrs A permission to appeal her ruling. However, they can approach the Court of Appeal directly.

In a statement, the couple said they were disappointed with the ruling. Their lawyers added: "Mr and Mrs A now intend to apply for an adoption order in respect of the twins in order that Mr A will regain his legal standing." They also expressed sympathy for Mr and Mrs B.

The black couple asked for time to consider the implication of the ruling. They thanked Mr and Mrs A for their "sensitivity and understanding".

In a statement, their solicitors said: "After today's judgement, they need to time to reflect on where the judgement leaves them."

I think it is a profoundly sensible judgement Suzi Leather, HFEA

Dame Elizabeth reiterated that the individuals involved cannot be named by the media.

"These two families have gone through an astonishingly traumatic experience," she said.

"I can't think that anybody could consider any experience could be more traumatic than this and they will have to come to terms with my judgment and its consequences unless or until the Court of Appeal say that I am wrong."

She added: "Just have a great deal of sympathy for these families and the children and leave them alone."

Suzi Leather, chair of the Human Fertilisation and Embryology Authority which regulates IVF treatment in Britain, welcomed the ruling.

"I think it is a profoundly sensible judgement. It recognises the twins should stay with the couple they regard as their parents," she said.

Ms Leather told BBC News this case was a one-off.