Unreasonable behaviour’ is the most common ground for divorce in UK divorce law. Petitioners must show that one of the parties to the marriage has behaved in such an unreasonable manner that the other finds it intolerable to live with him or her, and as a result the marriage has irretrievably broken down.
So what constitutes unreasonable behaviour? At the milder end examples include one partner refusing to get a job and relying on the other financially, being antisocial or a workaholic. At the more serious end it could include habitual drunkenness, drug taking, running up debts or violence.
Whatever the specifics, allegations of unreasonable behaviour are not subject to a great deal of scrutiny by the court if both parties are agreed on divorce. The courts understand that if one party to a marriage feels so strongly about it as to issue a divorce petition then the marriage has indeed irretrievably broken down and it would be futile to pretend otherwise.