Twins who were separated at birth married each other without knowing that they were brother and sister, a peer has claimed.

The couple were adopted as babies by different families, and neither was told that they had a twin. They met, fell in love and got married before discovering that they were blood relatives.

Lord Alton of Liverpool, who was told about the case by a High Court judge, told the House of Lords that the British couple were then granted an annulment at a special hearing at the High Court in London. Judges in the Family Division ruled that the marriage had never been valid.

“For them it was a terrible tragedy,” said Lord Alton, who declined yesterday to name the judge who had told him about the case and said that he had no further details.

Experts said that the trauma both of being separated and of discovering that they were twins in such circumstances would have had serious psychological consequences for the pair.

Lord Alton, who opposes parts of The Human Fertilisation and Embryology Bill now being debated in the Lords, argued that the twins’ experience demonstrated the need to strengthen a child’s right to know the identity of his or her biological parents.

He called on the Government to “think again” about the Bill, which contains no requirement for the birth certificates of children conceived by egg or sperm donations to include this fact, despite calls from some MPs and peers for it to do so.

Yesterday Lord Alton said that the case of these twins “outlines the importance of knowing your identity, knowing who you are and your genealogy. This is to prevent incestuous relationships, but also for reasons of genetics and disease prevention.

“I think there needs to be more clarity in public records. A birth certificate is a historical document, it is not about your social circumstances.”

People conceived from egg and sperm donations made since April 2005 have the right to know their parents’ identity. But Lord Alton said: “Although you have the right to inquire, there is no duty on anybody to tell you that you are donor-conceived.”

Evan Harris, the Liberal Democrat science spokesman, said that he was “disappointed that Lord Alton was using one couple’s million-to-one chance personal tragedy to make irrelevant political points. If you know you are donor-conceived or have a suspicion, you can check whether you are related to your partner.”

He added that the twins’ case was “absolutely nothing to do with the regulation of fertility treatment”.

Mr Harris added: “The suggestion that a birth certificate should be a record of your biological rather than social parentage implies enforcing blood tests on everyone. An estimated 10 per cent of children are being brought up by people who aren’t in fact their father. For the State to go wading into that would destroy happy families.”

Audrey Sandbank, a family psycho-therapist and consultant to the Twins and Multiple Births Association, said that it was in some senses unsurprising that the twins were attracted to each other when they met. “This pair had one bereavement when they were adopted separately and now have another one with having to split.”

Mo O’Reilly, Director of Child Placement for the British Association for Adoption & Fostering, said: “Thirty or forty years ago it would have been more likely that twins be separated and brought up without knowledge of each other. Today, however, adopted children grow up with a greater knowledge of their birth families – and organisations try to place brothers and sisters together.”

What the Bill means

— The Human Fertilisation and Embryology Bill updates the 1990 fertility and embryo research laws

— It removes the need for fertility clinics to take into account a child’s need for a father

— A scrutiny committee of MPs and peers recommended adding details of donor conception to birth certificates but this was rejected by the Government

— The Bill sets out a schedule of circumstances in which controversial techniques such as embryo screening are permitted and bans sex selection for social reasons

— It gives fuller parental rights to gay couples

Source: Department of Health

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