Divorce is the irretrievable breakdown of a marriage and has to be based on one of four possible grounds,

One year separation with consent of both parties. This is the most commonly used ground (49% in 1998). The parties must not have any continuing financial dispute. One spouse will raise proceedings and the other spouse must sign a form of consent. Where there are no children under 16 there is a quick simplified procedure. If there are any children under 16 evidence has to be produced in affidavit form (statements signed in front of a notary public) about the child's welfare. Court appearances should not be necessary.

Unreasonable behaviour of one spouse. This is the second most common ground (24% in 1998) and is used where the spouse seeking divorce is not prepared to wait for 2 years separation and/or the spouse will not sign a consent form. Evidence of the unreasonable behaviour has to be produced which is verified by at least one supporting witness. Unreasonable behaviour can cover many formats and is not just restricted to the drunken man beating up his wife after a Saturday night in the pub. Other examples include habitual neglect of the family by excessive work & social commitments or working abroad and being verbally abusive at home visits or extra marital sexual activity (including homosexual relations or associating closely with members of the opposite sex falling short of adultery). It is rare for evidence actually to be given in court unless the case is fully defended. Use of affidavit evidence means that the parties may not have to appear in court.

Two years separation. This process is very similar to ground 1 except that no signed consent of the spouse is required.

Adultery. If one spouse is living with someone else private investigators can be hired to establish the evidence of adultery. A direct approach by knocking at the couples door can be made to interview them and check the sleeping arrangements. Otherwise they can be spied upon by watching the house to observe when they go to bed and get up. Where there is no living in sin scenario other types of evidence will be needed such as diaries and letters. In the infamous Duke of Argyll divorce action from 1963 diaries and photographic evidence (including the Duchess performing oral sex on a "headless man") was obtained by forcing open her locked desk.