Exlusionary Discretion

Besides exclusionary rules, there are also discretionary discretion. 
In terms of exclusionary discretion, the trial judges in criminal trial may exclude evidence from the prosecution which is relevant and admissible ( with the condition that it is not excluded by the exclusionary rule).
The discretion is conferred on the judge by s78 of the PACE Act 1984 and common law. 
The purpose of the statutory discretion by s78 of the PACE Act 1984 is to prevent any admission of the relevant evidence from affecting adversely the fairness of the proceeding. 
The purpose of the common law discretion is to prevent the prejudicial consequences which  outweigh the probative value. As a result, the evidence is excluded. 
The discretion to exclude evidence is applicable only to particular circumstances.