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Unfairness

Under English law, evidence that would otherwise be admissible at trial may be excluded at the discretion of the trial judge if it would be unfair to the defendant to admit it.

Evidence of a confession may be excluded because it was obtained by oppression or because the confession was made in consequence of anything said or done to the defendant that would be likely to make the confession unreliable. In these circumstances, it would be open to the trial judge to exclude the evidence of the confession under Section 78(1) of the Police and Criminal Evidence Act 1984 (PACE), or under Section 73 PACE, or under common law, although in practice the confession would be excluded under section 76 PACE.

Other admissible evidence may be excluded, at the discretion of the trial judge under 78 PACE, or at common law, if the judge can be persuaded that having regard to all the circumstances including how the evidence was obtained "admission of the evidence would have such an adverse effect on the fairness of the proceedings that the court ought not to admit it."

In the United States and other countries, evidence may be excluded from a trial if it is the result of illegal activity by law enforcement, such as a search conducted without a warrant. Such illegal evidence is known as the fruit of the poisonous tree and is normally not permitted at trial.