Contempt
Contempt of Court is the body of law which protects the integrity of the legal process from outside influences. Contempt can take many forms but by far the most serious for the BBC is publication when legal proceedings are said to be "active".
In most criminal cases, the "active" period starts with the granting of an arrest warrant, the arrest of a suspect, or the issue of a summons (in Scotland a complaint) or indictment. This may be well before a person is charged.
Once a case is "active", anything which creates a substantial risk that the course of justice in those proceedings will be seriously prejudiced or impeded will be a contempt of court. This is the case regardless of intent. A serious prejudice might include, for example, the publication of previous convictions.
These rules apply to all courts and tribunals exercising the judicial authority of the state. However, the risk is highest when the case is due to be heard by a lay jury (e.g. in criminal trials) and particular care should be taken with coverage immediately before a jury trial. Reports of the trial itself are safe so long as they are fair and accurate.
It is now possible for the courts (except in Scotland) to order third parties - such as the media - to bear the costs of a trial abandoned as a result of publication of material, even if this does not amount to a contempt of court.