I came across this whilst researching this afternoon. Prior to the Matrimonial Causes Act of 1857, the only way to get a full divorce which allowed re-marriage was to obtain an Act of Parliament by proving adultery or life-threatening cruelty. To the left is the first page of one such Act, the Addison/Campbell Divorce Act 1801. This, however, was no ordinary Divorce Act. It was, in fact, the first to be obtained by a woman - Jane Campbell divorced her husband Edward Addison on the grounds of adultery with her sister Jessy Campbell. Unusually for the time, Jane was also granted custody of her children.
The Act can be found in the Parliamentary Archives, and includes a transcript of the evidence of Amelia Laugher, maid to Jessy Campbell, who testified to the relationship between Jessy and Edward Addison. Apparently, the Archives holds the records of divorces obtained between 1670 and 1857, including the initial petitions to the House of Lords, Acts, Bills, amendments and copies of earlier proceedings in the ecclesiastical courts. One dreads to think how much this procedure would have cost - no wonder it could only be undertaken by the rich.