R v Sang [1979] UKHL 3

The appellant pleaded guilty to conspiracy to utter counterfeit banknotes after the trial judge ruled he had no discretion to exclude prosecution evidence on grounds the offence was induced by an agent provocateur. The House of Lords confirmed entrapment is no defence in English law and defined the limited circumstances in which judges may exclude admissible evidence.

Facts

The appellant, Sang, was indicted for conspiracy to utter counterfeit American banknotes. Before trial, his counsel alleged that Sang had been induced to commit the offence by an informer acting on police instructions, and that he would not have committed the crime but for such persuasion. Counsel sought a ‘trial within a trial’ to establish these facts, arguing the judge had discretion to refuse to allow the prosecution to prove its case if the offence was instigated by an agent provocateur.

Judge Buzzard ruled that even assuming the offence was so instigated, he had no discretion to exclude the prosecution’s evidence. Following this ruling, Sang withdrew his not guilty plea and pleaded guilty. The Court of Appeal dismissed his appeal and certified a point of law of general public importance.

Issues

Primary Issue

Whether a trial judge has discretion to refuse to admit prosecution evidence where the offence charged was instigated by an agent provocateur.

Broader Certified Question

Does a trial judge have a discretion to refuse to allow evidence—being evidence other than evidence of admission—to be given in any circumstances in which such evidence is relevant and of more than minimal probative value?

Judgment

The House of Lords unanimously dismissed the appeal and confirmed that entrapment does not constitute a defence under English law.

Lord Diplock stated:

“The fact that the counsellor and procurer is a policeman or a police informer, although it may be of relevance in mitigation of penalty for the offence, cannot affect the guilt of the principal offender; both the physical element (actus reus) and the mental element (mens rea) of the offence with which he is charged are present in his case.”

On the scope of judicial discretion, Lord Diplock formulated the answer to the certified question:

“(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.”

Lord Salmon emphasised:

“A man who intends to commit a crime and actually commits it is guilty of the offence whether or not he has been persuaded or induced to commit it, no matter by whom.”

Lord Scarman explained the rationale:

“The role of the judge is confined to the forensic process. He controls neither the police nor the prosecuting authority. He neither initiates nor stifles a prosecution.”

Legal Principles

The House established several important principles:

• Entrapment is not a defence in English law, though it may be relevant to mitigation of sentence
• Judges have discretion to exclude evidence where prejudicial effect outweighs probative value
• Judges may exclude confessions or admissions obtained improperly from the accused after the offence
• Judges have no general discretion to exclude relevant admissible evidence simply because it was obtained by improper means
• The judge’s function is to ensure a fair trial, not to discipline the police or prosecution

Implications

This decision firmly established the limits of judicial discretion to exclude evidence in criminal trials. It confirmed that while judges have an overriding duty to ensure fair trials, this does not extend to creating procedural defences unknown to substantive law. The decision clarified that police misconduct in obtaining evidence, including the use of agents provocateurs, is properly addressed through sentencing, civil remedies, or disciplinary proceedings rather than exclusion of evidence. The case remains a foundational authority on the admissibility of evidence and the scope of judicial discretion in criminal proceedings.

Verdict: Appeal dismissed. The House of Lords held that Judge Buzzard was correct in ruling he had no discretion to exclude prosecution evidence on the ground that the offence was instigated by an agent provocateur. Entrapment is not a defence in English law, and judicial discretion to exclude admissible evidence does not extend to excluding evidence of crimes merely because they were induced by police informers.

Source: R v Sang [1979] UKHL 3