Adversarial or Non-Adversarial Court System
The UK has a predominantly adversarial court system in which the parties investigate their own cases and call their own evidence. A case is argued by two opposing sides who have the primary responsibility for finding and presenting facts.
In civil cases, the claimant tries to prove that the defendant has committed a breach of a legal duty and the defendant argues that it did not commit such a breach. The introduction of the Civil Procedure Rules (CPR) in 1999 has to some extent altered the role of the judge in civil cases to allow for a more interventionist judicial case management role but his or her role in the trial is generally a passive one.
In a criminal case, the Crown (prosecutor) tries to prove that the defendant is guilty and the defendant's lawyer argues for their acquittal (that is, that they did not commit the crime they are charged with).