There's only one basic ground for divorce: the irretrievable breakdown of the marriage. You can prove irretrievable breakdown by establishing one or more of the following 'facts':

Fact A. Adultery

You must prove that either through actual admission or through sufficient circumstantial evidence your spouse has had sexual intercourse with another person of the opposite sex and that you find it intolerable to live with your spouse. If a sexual liaison short of sexual intercourse has taken place, it's suggested that the unreasonable behaviour ground is used.

You can name the other person involved as a co-respondent but this isn't essential and can have serious consequences. Doing so can make the proceedings more acrimonious, more complicated and more drawn out. It's therefore usually best to avoid naming a co-respondent. If you wish to name the other person, you should take legal advice before doing so.

Adultery can be used as the basis for a divorce petition whether you and your spouse are still living together or have separated, but in either case not more than six months must have elapsed since you became aware of the adultery before the petition is sent to the court, unless the adultery is continuing.

Fact B. Unreasonable behaviour

You must show that your spouse has behaved in such a way that you cannot reasonably be expected to live with him or her. Unreasonable behaviour is now the most common fact on which to prove the ground for divorce in England and Wales. In an unreasonable behaviour petition, the petitioner sets out a number of allegations against the respondent.

These allegations might include references to excessive drinking or financial extravagance, for example; but it's worth bearing in mind that the court doesn't insist on really severe allegations of unreasonable behaviour in order to grant a divorce. Relatively mild allegations such as devoting too much time to a career, having no common interests or pursuing a separate social life may well suffice. Using mild allegations may also make it easier to agree the contents of the petition with your spouse before you issue it.

Fact C. Desertion

Where your spouse deserted you without your consent for a continuous period of at least two years; this fact is almost never used. This ground of divorce has recently been abolished in Scotland.

Fact D. Two-year separation in England and Wales/one-year in Scotlan

By consent you and your spouse have been living apart for at least two years in England and Wales, or one year in Scotland, immediately preceding the presentation of the petition (or 'Initial Writ' in Scotland) and you both agree to a divorce.

Fact E. Five-year separation in England and Wales/two-year in Scotland

You and your spouse have been living apart for at least five years in England and Wales, or two years in Scotland, immediately preceding the presentation of the petition (or 'Initial Writ' in Scotland). In this instance, your spouse need not consent to the divorce.

Law stated as at 1 September, 2007