The courts have two mediums through which they can express their power to exclude certain prosecution evidence; discretion as defined in the common law, and statutory discretion as detailed in section 78 of the Police and Criminal Evidence Act 1984 (PACE).1 Academic commentators suggest that it is unclear exactly how judicial discretion operates in practice, however, what is agreed on is that with the introduction of PACE the overall effect is that evidentiary exclusion can be justified on broader terms.2
Previous to the Act coming into force on the 1st January 1986, the exclusion of evidence obtained improperly was rare in application by the courts. Crompton J in R v Leatham  opined that ‘it matters not how you get it, if you steal it even, it would be admissible in evidence’, and in the case of Kuruma v R , Lord Goddard CJ gave the view that the courts would exclude evidence obtained if it operated unfairly against the accused.3 More recently in the case of R v Sang  Lord Diplock reaffirmed his predecessors’ conclusions by offering that apart from the exception of R v Payne :
(1) A trial judge in a criminal trial has always a discretion to refuse to admit evidence if in his opinion its prejudicial effect outweighs its probative value. (2) Save with regard to admissions and confessions and generally with regard to evidence obtained from the accused after commission of the offence, he has no discretion to refuse to admit relevant admissible evidence on the ground that it was obtained by improper or unfair means.4
The case of Sang dealt specifically with evidence obtained by an “agent provocateur”, but from this it became the accepted authority relating to courts not being concerned with how evidence was obtained particularly with judges not viewing their function to police the police.5 Whilst this view was accepted, it should not detract from the fact that the judiciary acknowledged their discretion of relevant evidence was important, particularly concerning a judge’s duty to ensure a fair trial.
It appears that the case law is rather generous to the prosecution with regards to judges’ discretion when deciding whether to exclude any evidence obtained dubiously; however, one could argue it is equally restrictive. What is quite clear is that the common law concern is not how evidence is obtained, but its subsequent effect. The introduction of PACE has broadened the requirements for judicial discretion of exclusion.6 The statute clearly places emphasis the court’s power to ‘refuse to allow evidence’ that would have ‘an adverse effect on the fairness of the proceedings’ which is arguably not dissimilar from common law.7 What the statute does add, however, is that the courts must have regard to ‘the circumstances in which the evidence was obtained’.8 It is important to note at this stage that the introduction of PACE has not replaced the common law, there is overlap with further content in the statute as the drafters included section 82(3) which preserves any power of the court to exclude evidence if the prejudicial effect far outweighs the burden of proof on the accused.9 However in R v Khan  Lord Taylor demonstrated a rather restrictive view when he commented that it is ‘only necessary to consider the question of the exercise of discretion under s 78’, thus contending that, in practice, it is the statutory provision that takes precedent over the common law.10 Section 78 of PACE has broadened the restrictions of excluding improperly obtained evidence in two main ways: one, the courts can look at how evidence was obtained, which may cover cases of entrapment of the use of “agent provocateurs”, and; two,...