Twins marry each other

The British couple have now been granted an annulment after a special High Court hearing. Judges ruled the marriage had never validly existed.

Full details of how the brother and sister fell in love and married have been kept secret, along with their identities. But the Evening Standard has learned that they were separated soon after birth.

Each was then adopted by different families but neither was told they had a twin. The couple had no idea they were blood relatives until after their wedding.

The case was heard recently in the High Court's Family Division. Experts warn that it highlights the need for the rights of children to know the identity of their parents to be strengthened.

Professor Lord Alton, who uncovered the case, said new reforms drawn up by ministers threatened to undermine existing rights. The changes, now being debated in the House of Lords, would also relax rules on who can have fertility treatment.

Critics say they will weaken further the link between children and their biological parents - and even effectively end the need for fathers.

Lord Alton said: "The right for children to know the identity of their biological parents is a human right. There will be more cases like this if children are not given access to the truth. The needs of the child must always be paramount."

The Government has been facing fierce opposition over sweeping changes to fertility laws in the Human Embryology and Tissues Bill. Under the proposed law, fertility clinics will not be able to bar single women and same sex couples from treatment. Instead, doctors must ensure that patients can offer "supportive parenting".

Ministers have already been forced to rewrite the Bill following objections by peers to the original wording. It had stated that children born through fertility treatment needed a "social network", not a father and mother.

The Lords will vote on the revised bill on Tuesday.

Those pushing for the role of fathers to be recognised as vital include Baroness Ruth Deech, a former head of the Government's fertility watchdog, the Human Fertilisation and Embryology Authority (HFEA).

However fertility treatment pioneer Lord Winston said that the call for a such a "father clause" would discriminate against career women.

He said: "This is prejudiced against women who have paid their taxes, been well educated and delayed motherhood because they are working hard. If they are left without a partner and still want a baby [with a donor], this would prejudice their treatment and ask doctors to make a value judgment about them."

Lawyer Natalie Gamble, an expert on fertility regulations, said: "Equality rules mean clinics have to give treatment to single women and same sex couples anyway. The Government doesn't need to enshrine this in new laws."

Annulments are usually heard at county court, but can go to the High Court if cases are particularly complex. Marriages can be annulled if one of the parties was under 16 at the time of the wedding, if it was a bigamous union, or if the couple are closely related.

The latest figures, for 2005, show 251 marriages were annulled that year. There is no breakdown of how many cases fell into each category.