That reminds me of a joke Ronnie Barker told Groutie in an episode of Porridge.
A woman wants to divorce her husband, who has been in prison for quite a few years. So she goes to a solicitor who tells her she can obtain a divorce if her husband is guilty of cruelty to her. She thinks about it and says she can't really accuse him of that.
Then the solicitor says she can accuse him of desertion. However she says he didn't really desert her, the police took him away.
Then the solicitor says that she can divorce him for adultery and she smiles and says 'That's it! He is definately not the fathher of my child.
Sorry about Groutie, but he had a good innings.