Shock for the married couple who discovered they are twins separated at birth

It was only after they married, according to Lord Alton, that they became aware of the "appalling" truth and sought to have their union dissolved. Marriages can be annulled in cases where there is a "prohibited degree of consanguinity" - blood relationship.

The case came before a judge, sitting in private, in the High Court Family Division where, according to Lord Alton, "he had to deal with the consequences of the marriage that they entered into and all the issues of their separation".

No other details about the couple, their relationship, or the annulment have been made public but the peer added: "It was appalling for this couple to discover they were married to a close relative.

"And I believe the Government will leave itself open to class actions in the future if it collaborates in keeping information of this kind from children who have been donor-conceived."

Lord Alton and his supporters want the genetic history of a child recorded on its birth certificate.