Chief Justice Ma: 1. I agree with the judgment of Lord Phillips of Worth MatraversNPJ. Mr Justice Ribeiro PJ: 2. I agree with the judgment of Lord Phillips of Worth MatraversNPJ. Mr Justice Tang PJ: 3. I agree with the judgment of Lord Phillips of Worth MatraversNPJ. Mr Justice Fok PJ: 4. I agree with the judgment of Lord Phillips of Worth MatraversNPJ. Lord Phillips of Worth Matravers NPJ: Introduction 5. This appeal raises the question of the circumstances in which a defendant should be permitted to adduce evidence of improper conduct involving police witnesses called by the prosecution that is alleged to have taken place on an occasion wholly unconnected with the offence with which the defendant is charged. Unusually that question arises in the context of a voir dire. The appellant’s case in a nutshell is that the trial judge wrongly refused to admit evidence at the voir dire which, if admitted, might have led her to exclude from the trial evidence of damaging statements alleged to have been made to the police by the Appellant at the time of his arrest, and subsequently made by him at a video-recorded interview. 6. On 19 January 2011 the Appellant was convicted after a trial before Beeson J and a jury of two counts of trafficking in a dangerous drug (Counts 2 and 3) and was acquitted of a count of manufacturing dangerous drugs (Count 1). The Appellant was sentenced to 9 year’s imprisonment on Count 2 and 23 year’s imprisonment on Count 3, to run concurrently. A significant part of the evidence adduced against the Appellant consisted of statements made by the Appellant to the police. In a voir dire held before the jury were empanelled the Appellant had unsuccessfully challenged the admissibility of these statements. At the trial he did not give evidence but relied upon parts of the statements as being exculpatory. The evidence at the trial 7. On 9 July 2009 police officers in a raiding party led by Senior Inspector K.M.Chan laid an ambush outside a flat at Parkland Villas in Tuen Mun. Three men came out, the Appellant, Hung Wai-Yip (“Hung”) and Yuen Kin-san (“Yuen”). Hung and Yuen were to be jointly charged with the Appellant. The police intercepted the three men and there was a struggle. Hung was carrying a white carrier bag containing packets of cocaine (the subject of Count 2). Upon finding these packets the police arrested the three men and cautioned them for trafficking in dangerous drugs and obstructing a police officer in the execution of his duty. The Appellant then said “I only received $1000 from someone for delivering coke for him. I know nothing else”. 8. Keys were found in the appellant’s trouser pocket, that were used to gain access to the flat. More cocaine was found inside the flat (the subject of Count 3) and equipment for manufacturing dangerous drugs (the basis of Count 1). The Appellant remarked: “I did not know there was so much coke here, Ah sir”. 9. DPC 50049 (for simplicity I shall refer to police constables by their numbers rather than by name), who was the officer who arrested the Appellant, recorded these events in his notebook. Subsequently, at Tuen Mun Police Station, in relation to each statement recorded as made by the Appellant, the Appellant endorsed the notebook with a signed declaration that the relevant part of the notebook had been read out to him by DPC 50049, that he had also read it for himself, and that he had made the statement set out in the notebook of his own free will. 10. CCTV recordings produced by the prosecution showed that the Appellant had visited the flat on a number of occasions between 3 and 9 July 2009. 11. On 10 July the Appellant submitted to an interview that was video-recorded. He declined the offer of a lawyer and confirmed that he had declined a similar offer after his arrest. He confirmed the remarks that he had made after he had been arrested and cautioned. He said that he had gone to the flat with Hung, who was a friend, looking for Yuen at his request. When the police team arrived he had not realised that they were police officers and had given one a push. When the police produced their warrant cards he no longer struggled. He said that he had borrowed the keys of the flat to go to the toilet. He said that he had asked Hung to go with him to the flat because he had been offered $1000 to help others deliver coke, but he did not know what coke was. When he discovered that it was a dangerous drug he left the flat immediately. He was only in the flat about 10 minutes. 12. At the trial the Appellant did not give evidence. His counsel, Mr Ross, relied in his submissions to the jury on that part of the interview in which the Appellant said that he did not know what the “coke” was that he had been asked to help deliver, that he had left the flat when he discovered that the “coke” was a dangerous drug and that he only had the keys to the flat because he had borrowed them to go to the toilet. The voir dire: objections to admissibility 13. In a document dated 31 December 2010 the Appellant’s counsel and solicitor set out objections to the admissibility of both the statements that the Appellant was alleged to have made after his arrest on 9 July 2009 and the video-recorded interview on the 10 July. This included the following allegations: (i) All three defendants were assaulted by police officers as they came out of the flat on 9 July. The Appellant was pushed back into the flat. He was kicked several times. He was handcuffed and hooded with the eyeholes in the hood at the back of his head, so that he could see nothing. DPC 50049 placed some keys next to him, saying “this is yours”, which he denied. DPC 50049 then hit his head and said “you’d better not talk too much”. (ii) When the police officers brought the Appellant to the police station they ordered him not to get a lawyer and to obey, otherwise he would suffer and be beaten. (iii) DPC 50049 made the Appellant endorse the contents of his notebook with the declarations and signatures without permitting him to read what those contents were. (iv) The Appellant said that he wanted a lawyer before his video-recorded interview but was told by DPC 503 that he did not need one and that he should respond in the interview to the question of whether he wanted a lawyer by “no need”, in which event he “would not be suffering”. (v) DPC 503 told the Appellant to say in the interview that he had the keys because he wanted to go to the toilet and that this was the first occasion on which he had visited the flat. He later added that the Appellant should say that he had gone there to deliver coke for $1000 because that was already in DPC 50049’s notebook. He said that if the Appellant said that as soon as he came to know that coke was cocaine he immediately refused to do it and left the flat, then he would be alright – “trust me”. The Appellant followed these instructions when answering questions in the video interview. The voir dire: the police evidence 14. DSIP Chan and four members of his team who took part in the raid on 9th July, including DPC 50049 and DPC 503 gave evidence on the voir dire that was held between 5 and 7 January 2011. Both when giving evidence in chief and under cross-examination they denied the allegations set out in the objections to admissibility. There had been an initial struggle at the time that the three men were arrested, but after that no violence had been used. A hood was put over the Appellant’s head, but only at the stage when he was escorted from the flat to the police station. The keys to the flat were not planted on him. He made the statements that were subsequently recorded by DPC 50049 in his notebook. Those statements were read to him and he read them for himself before he wrote and signed the declarations in the notebook. No threats were made before the video-recorded interview, nor was he coached as to what to say at that interview. He was not prevented or discouraged from having the assistance of a lawyer. The voir dire: the Appellant’s evidence 15. The Appellant opted to give evidence at the voir dire. He said that when he and the other two men came out of the flat at Parkland Villas a group of people rushed out and assaulted them. They were pushed back into the flat where the assault continued. He fell to the floor where he was kicked by DPC 50049 and 34311. A hood was then put over his head with the eye-holes at the back. He was punched on the head by DPC 50049. He was permitted to go to the toilet and he was given some water. Before they left the flat a police officer told them not to look for a lawyer and to obey the police otherwise they would suffer for a long time. They were then taken to the Tuen Mun Police Station where DPC 50049’s notebook was prepared and the video-recorded interview took place in the circumstances alleged in the ‘objections to admissibility’ summarised above. 16. I now come to the part of the voir dire that has given rise to this appeal. It relates to attempts to introduce evidence of a subsequent drugs raid by a team led by DSIP Chan. The raid on 26 August 2009 17. On the night of 26 August 2009 DSIP Chan led his team on a raid on a house at Ma Tin village. Two brothers were in the house, Wong Tsz Him, the elder brother, who was asleep in bed, and his younger brother Wong Tsz Pang, who was watching television. The solicitors acting for the appellant learnt of this raid when a press report of it, which included a photograph of the aftermath of the raid, was drawn to their attention. On 2 January 2011 they took a witness statement from the elder brother (“Mr Wong”). This described how the door of the house was forced open and the two brothers were confronted by a group of 6 to 8 men coming up the stairs in line. The man at the front had a crowbar. The man behind punched Mr Wong once in the chest and pushed him back onto a sofa. A second man held him down on the sofa by the neck. A third man hit his right ear and neck once. Someone else punched his back and waist three or four times. He was then handcuffed and realised that his assailants were policemen. Someone then flung a blanket over his head and he received at least 10 further punches to the back. After about 10 minutes the blanket was removed and he saw that his brother was also handcuffed. The house was searched but nothing was found. The handcuffs were then removed from the brothers. The Wongs’ parents then arrived. Mr Wong asked for a drink of water and for permission to go to the toilet and to see a lawyer. These request were refused. Subsequently, by which time a considerable number of villagers had gathered outside the house, uniformed police and an ambulance arrived and Mr Wong was taken to A and E for treatment. After this, at about 2 a.m., Mr Wong made a formal complaint that he had been assaulted by police officers to Yuen Long Police Station. The voir dire: cross-examination of police witnesses 18. In the course of cross-examination Mr Ross asked DPC 50049 if he had taken part in the raid on 26 August at Yuen Long. He replied that he had not. He was then shown newspaper photographs taken of the aftermath of that raid. He identified that two of the police officers shown in the photographs were DSIP Chan and DPC 54856, both of whom had taken part in the raid on 9 July. DPC 34311was not shown in the photographs and when he came to give evidence on the voir dire it was not suggested to him that he took part in the raid on 26 August. It is common ground that he did not. 19. When DSIP Chan came to give evidence at the voir dire Mr Hemmings for the prosecution objected to his being asked questions about the raid on 26 August on the ground that this was part of an on-going investigation involving not only DSIP Chan’s team, but other teams. Mr Ross stated that he wished to cross-examine in order to point out “any similarities in the…improper way that the operation was carried out on the latter occasion”. The judge ruled “I think you should just put it as a general question that rough tactics were used at the arrest…I do not think you can put it any more than that”. 20. Mr Ross then put to DSIP Chan that at the raid on the 26 August either he himself used violence or he witnessed his officers using violence. To this he replied simply “no”. That was the extent of the cross-examination of the inspector on this point. 21. When DPC 54856 gave evidence at the voir dire he confirmed that he had taken part in the raid on 26 August. He was asked whether he had seen anyone inside the premises with a blanket over his head and he said that he had not. He was asked whether he had seen violence used on the occupants of the premises and he said that he had not. The voir dire: The application to call Mr Wong 22. Mr Ross gave no notice that he intended to call Mr Wong to give evidence at the voir dire. Before doing so, however, he informed Mr Hemmings that he was about to call a civilian who was involved, in a way that he did not specify, in the raid of 26 August. Mr Hemmings then objected to the admission of this witness’s evidence on the ground that it went to an entirely peripheral matter. Mr Ross sought to justify calling Mr Wong on the ground that his evidence fell within “an exception” to the “finality rule when there is bad character alleged”. He said that he anticipated that Mr Wong “will give evidence of the propensity of this team to commit similar kind of raids with accompanying violence as they did in this case”. The judge ruled: “Well, I don’t see that this is relevant evidence or viable evidence and I am not allowing this witness to be called”. 23. At the end of the voir dire the judge ruled that she was satisfied that the Appellant had made the statements attributed to him at the scene of the arrest and subsequently at the video-recorded interview and that this was not a case where she should exercise her discretion to exclude the evidence in question. 24. In the following week, before the trial began, Mr Ross renewed his application to admit the evidence of Mr Wong, though it is not entirely clear to me from the transcript whether he was seeking to re-open the voir dire or seeking leave to adduce the evidence of Mr Wong at the trial itself. He stated that Mr Wong would make specific allegations against two of the police witnesses who had given evidence at the voir dire, namely that one had put a blanket over the head of Mr Wong and another had punched him in the chest on the occasion of the 26 August raid. After argument the judge refused to amend her earlier ruling. The Appeal to the Court of Appeal 25. The Appellant applied to the Court of Appeal for leave to appeal against conviction[1]. One of the grounds of appeal was that the judge wrongly refused to receive the evidence of Mr Wong at the voir dire. His application was dismissed[2]. After consideration of relevant authorities the Court explained its reasons for rejecting this ground of appeal in the following passage: “In the 2nd applicant’s case the evidential link between the 2nd applicant’s testimony and that of the prospective witness, Wong Tsz Him, as described to the judge, was weak and tenuous. Each of them had allegedly received a punch(s) and had their heads covered, one with a hood but the other with a blanket. There was no other supporting relevant evidence. It was not suggested that the police officers had tried to force admissions from Wong Tsz Him. The two events were wholly unconnected investigations, separated in time by 7 weeks. Clearly, the nature of the cross-examination of the police officers did not go to an issue in the case. Rather, it was relevant to credibility only. Its relevance was tenuous at best and not of substantial probative value. We are satisfied that the prospective evidence was not such that fell within the exceptions to the ‘finality rule’ in respect of questions as to collateral matters, including credit. Accordingly, in our judgment the judge was correct to decline to receive that evidence.” 26. The Appeal Committee of this Court[3] granted leave to appeal on the ground that the following question of the requisite importance arose: “What is the correct principle for determining when a witness may be cross-examined as to past misconduct in a different case with a view to challenging his or her credit in the instant case; and for determining when, if at all, evidence may be led to impeach answers given by such witness in the course of such cross-examination.” The relevant law 27. Two basic common law principles as to the admission of evidence are in play on this appeal. The first is that no evidence is admissible unless it is relevant to an issue in the case. The second is that evidence should not be admitted if its probative weight is insufficient to justify the complexity that it will add to the trial[4]. Whether in a criminal or a civil trial the judge should be astute to prevent the primary issues becoming obfuscated as the result of the admission of evidence of insufficient significance to justify the additional burden that it will impose on the hearing[5]. These principles apply as much to a voir dire as they do to the trial itself. 28. In applying these principles it is helpful to distinguish between primary issues and collateral issues. Whether an event upon which the prosecution relies in fact occurred is a primary issue. Evidence that such an event did or did not occur is primary evidence. A collateral issue does not bear directly on whether a primary fact in issue occurred. It bears on the reliability of the primary evidence. The second principle normally applies only in relation to evidence that goes to a collateral issue. Evidence as to credit 29. The evidence that most often gives rise to the invocation of the two principles set out above is evidence as to credit. Where a witness gives evidence that is challenged, the veracity of that witness may be put in issue. The party challenging that evidence may wish to ask questions in cross-examination about the conduct of the witness on other occasions for the sole purpose of showing that the witness is not the kind of person whose word can be believed. Such evidence of how a witness behaved on another occasion, or an issue as to this, is collateral to the primary issue of whether the evidence of the witness is truthful. 30. In a criminal trial the exploration of how a witness behaved on another occasion for the purpose of attacking his veracity is likely to distract the court, or the jury, from the primary issue of the behaviour of the defendant, to the detriment of the fairness of the trial. For this reason there are long established common law rules of practice that restrict the extent of such an exploration. In some jurisdictions these rules have been codified[6]. The codification reflects the fact that this is not an easy area of the law to apply in practice and has proved a fertile source of appeals. 31. In this jurisdiction the relevant law has not been codified. It reflects principles applied in other common-law jurisdictions, particularly England and Wales, but in recent times has not always followed the approach of the courts of those jurisdictions to the detailed application of the basic principles. The approach in this jurisdiction was clearly set out by Li CJ in HKSAR v Wong Sau Ming[7] and the general principles that he set out merit repetition: 23. In this context, the relevant general principles are as follows. First, where the veracity of the witness is challenged on cross-examination as to credit, subject to the judge's discretion to disallow improper questions, cross-examination about discreditable acts is widely permitted. See Cross and Tapper on Evidence (9th ed., 1999) p.306. Its purpose is of course to show that the witness ought not to be believed on oath. 24. Secondly, the cardinal test of relevance in the law of evidence applies to such cross-examination. The subject matter of the cross-examination must be relevant to the witness's veracity. Relevance is a matter of degree. 25. Thirdly, in applying the test of relevance, the court should in its discretion usually permit questions in cross-examination as to credit if the truth of the imputation conveyed would materially affect the court's opinion as to the witness's veracity on the subject matter of his testimony. Conversely, questions in cross-examination as to credit are usually not permissible if the truth of the imputation conveyed would not have any material impact on such opinion. The imputation may relate to matters which are so remote in time or are of such a kind that the truth of the imputation would not have any material impact on the court's assessment of the witness's veracity. cf Sankey LJ in Hobbs v CT Tinling & Co Ltd [1929] 2 KB 1 at p.51. The matters about which the witness is questioned in cross-examination as to credit must relate to his likely standing after cross-examination with the tribunal in question. See R v Sweet-Escott (1971) 55 Cr App R 316 at p.320. 26. Fourthly, as a general rule, answers to questions in cross-examination as to credit on any ground including veracity are final and evidence is not admissible to contradict them. See Harris v Tippett (1811) 2 Camp 637 at p.638; 170 ER 1277. This can conveniently be referred to as "the finality rule". The rule is conducive to a fair trial. Its rationale is that, as a matter of commonsense, a criminal trial should be kept within proper limits. The court should focus on the issues in the case. Its attention should not be diverted to collateral issues such as credit, the exploration of which may unnecessarily blur or confuse the real issues in a cloud of detail. Although the rule has sometimes been criticized, it is well-established and necessary. However, the distinction between questions going to the issues in the case and those going to credit is sometimes difficult to draw and in some cases, can be a rather thin one. 32. Li CJ goes on to refer to well established exceptions to the finality rule. He observes that at this point the Hong Kong jurisprudence does not follow the strict approach adopted in some of the English cases, so that English cases should not be regarded as having any precedent value in Hong Kong[8]. 33. Li CJ found it unnecessary to go into the exceptions to the finality rule but observed that they allow proof by independent evidence of matters which tend to affect the credibility of a witness. He added that as the common law developed in Hong Kong there might be possible room for the relaxation of the finality rule and that the list of exceptions was not closed. This statement accords well with a statement of basic principle made by Lord Bingham CJ in R v Zomparelli[9] when commending guidance given by Lord Lane CJ in R v Edwards[10], a decision which, on its facts, has been questioned both in this jurisdiction and in England[11]: “…a criminal trial should be focused on the central issue in the trial: whether the defendant is or is not proved to have committed the crime or crimes of which he is accused. Unless firm control is exercised with that principle in mind, it is only too easy for that central issue to become submerged in a mass of subsidiary and collateral issues which have only an indirect or marginal bearing on the central question…but…the judge’s overall and paramount duty is to ensure the fairness of the trial. The trial process must be fair to the prosecution; the scales of justice are not balanced if heavily over-weighted in favour of the defendant. But it must be fair also to the defendant. He is entitled to a fair trial as a matter of constitutional right. No rule of law can restrict the duty of the court to ensure a fair trial.” 34. I can summarise the position as follows. Cross-examination as to credit should be permitted in relation to any matter that, if proved, will diminish a witness’s credibility. This may be a failure to tell the truth on an earlier occasion, or some quite different type of misconduct, providing only that it bears logically on the weight that should be accorded to the witness’s word[12]. Where a prosecution witness denies, under cross-examination as to credit, that he has been guilty of misconduct of a kind that would damage his credibility, evidence that unequivocally rebuts his denial, such as a finding by a court or tribunal to this effect, should normally be admitted for that purpose. Where, however, the truth of the allegation of misconduct made against the witness cannot be determined without what is, in effect, a separate trial relating to that issue, the finality rule will normally preclude the calling of evidence to challenge his denial. Similar facts evidence 35. Evidence that goes simply to credit must be distinguished from another type of collateral evidence – similar fact evidence. Where the trial raises a primary issue as to whether a police witness, or indeed anyone else, acted in a particular way, the fact that he acted in the same way on another occasion may render it more probable that he acted as alleged. Where it is the conduct of the defendant himself that is in issue, special rules fall to be applied when deciding whether relevant similar fact evidence should be admitted. These are designed to protect the defendant against unfair prejudice. Where, however, similar fact evidence is alleged against a prosecution witness similar principles apply to those that apply to evidence as to credit, although the application of those principles will not be identical. 36. Before a witness can be cross-examined as to how he behaved on an occasion unrelated to the trial, it must be demonstrated that the cross-examination is relevant. The judge must be satisfied that the matters to be alleged in cross-examination will, if established, be relevant to the determination of a primary issue. Where similar facts are relied on this will depend, in part, on the nature of the conduct in issue and the degree of similarity between that conduct and the ‘similar fact’ conduct alleged. If this test of relevance is satisfied, the judge should permit the cross-examination. 37. It is at the second stage that the approach to similar fact evidence may differ from the approach to evidence that goes simply to credit. Evidence that goes simply to credit will almost always have limited significance. The fact that a witness is someone whose word cannot be trusted does not mean that his evidence is necessarily false. This is the justification for the application of the finality rule in respect of evidence that goes simply as to credit. Similar fact evidence may, however, be so cogent as to have substantial probative value. If conduct alleged against a witness on two different occasions has the same particular features, and there is no question of collusion between the witnesses to the two different occasions, this may be a cogent indication of the truth of what is alleged in relation to each occasion. Thus where a witness denies on cross-examination that he behaved in the manner alleged on either occasion, this will not necessarily preclude the admission of the similar fact evidence in rebuttal of his denial. The decision whether or not to permit similar fact evidence to be called will depend upon the facts of the particular case. The judge will have to weigh the impact that the similar fact evidence will have, if believed, against the dislocation that its introduction will cause to the trial process. 38. The difference between the approach to evidence that goes merely to credit and similar fact evidence is well demonstrated by the case of HKSAR v So Kam Tong[13]. On a voir dire the defendant, who was charged with murder, alleged that admissions that he had made had been induced by violence in that the police had slapped his left ear, punched his chest and abdomen and squeezed his genitals, as well as making threats and inducements to confess. The judge none the less ruled that his admissions should go before the jury. There existed a letter of complaint by another person who had been suspected of the murder to the effect that the same police team, including the same senior officers, investigating the same complaint at about the same time had squeezed his genitals in an attempt to extract a confession. This letter was not disclosed, for which reason the defendant’s conviction for murder was set aside on the grounds of procedural irregularity. The relevance of this case is the significance attached by the Court of Appeal to the matter not disclosed. “It went beyond credit. It went to an issue in the applicant’s case…The defence case was that the police were desperate to find the missing lady and that the two senior officers running the team were willing to use and countenance violence in order to locate her. The complaint which Chu had made provided potential support for the applicant to that end. It was evidence that was capable of doing more than merely damaging the credibility of the police officers, by reference, say, to their conduct on some other occasion and in some other case. It was evidence about the behaviour of one police squad and its directing officers at exactly the same time in the course of precisely the same investigation which they were undertaking in respect of the applicant. It had the potential, in other words, to bear on what truly happened to the applicant that night.”[14] The application of the law to the facts of this case 39. As I remarked at the outset the relevant legal principles apply as much to a voir dire as they do to the trial itself. On the voir dire, however, the judge is better able to control the evidence and less likely to be confused by collateral evidence than a jury, so he may well properly give the defence more latitude. 40. The wording of the question of law in respect of which the Appeal Committee gave leave suggests that this case is about the admissibility of evidence as to credit, and the basis upon which the trial judge gave permission to cross-examine suggests that she may have been under the impression that this was aimed at impugning the credibility of the police witnesses. As the Court of Appeal remarked: “Clearly, the nature of the cross-examination of the police officers did not go to an issue in the case. Rather it was relevant to credibility only. Its relevance was tenuous at best and not of substantial probative value.” 41. I agree with the last comment. The allegations made in cross-examination that violence had been used in the raid on 26 August had little bearing on the question of whether or not the police officers should be treated as truthful witnesses. If all that was in issue was credibility, the judge was unquestionably right to apply the finality rule and to refuse the application to call Mr Wong to give evidence. I would add that I do not consider it relevant that the evidence that Mr Ross wished to adduce related to events after rather than before those that gave rise to the prosecution. The relevant principles apply equally in either case. 42. Before us Mr Ross made it plain that his object in cross-examining the police witnesses and in seeking to call Mr Wong was to adduce similar facts evidence. His submission was that evidence of what took place on 26 August should have been admitted because of its similarity to what the Appellant alleged took place on 9 July. Had the judge had the benefit of this evidence she might have formed a different view as to the admissibility of the evidence of statements made, or alleged to have been made, by the Appellant. 43. As the Court of Appeal remarked[15]at no stage of the trial was the judge provided with a witness statement of the prospective evidence of Wong Tsz Him. Where defence counsel applies to adduce evidence of events that are unconnected with those that have given rise to the prosecution, whether on the basis that they are relevant as to credit or on the basis that they are relevant as similar facts evidence, and he has a witness statement setting out the evidence in question, he ought to place that statement before the judge. Counsel should adopt the procedure set out by Li CJ in relation to evidence as to credit in HKSAR v Wong Sau Ming at paras 41 and 45. All relevant material should be placed before the judge. Only in this way will the judge be in a position to make a properly informed decision as to whether the evidence should be admitted. In a jury trial this should, of course, take place in the absence of the jury. 44. What should the judge have decided had she been fully appraised of the evidence that the Appellant wished to adduce? What bearing, if any, did this have on the issues before her on the voir dire? The issues on the voir dire 45. The evidence given by the Appellant on the voir dire was of serious misconduct by the team led by DSIP Chan, in particular, DPC 50049. The most serious of these were: i) DPC 50049 recorded in his notebook incriminating statements attributed to the Appellant that were fabricated. ii) DPC 50049 made the Appellant write and sign declarations in his notebook that the statements in question had been read to him that he had read them himself and that they were true, without permitting him to read the statements. iii) DPC 50049 ‘planted’ the keys of the flat on him. iv) Police officers made threats that prevented the Appellant from seeking the assistance of a lawyer, notwithstanding that he wanted such assistance. v) DPC 503 prevailed on the Appellant to say in the video-recorded interview that he had been given the keys of the flat because he wanted to go to the toilet and that this was the first occasion on which he had visited the flat. That statement was, as DPC 503 was aware, demonstrably untrue because the police had video records of the Appellant visiting the flat on a number of occasions. 46. It was also the Appellant’s case on the voir dire that at the time that he was arrested he was kicked several times by DPC 50049 and DPC 34311, that after he was handcuffed a hood was placed over his head, with the eyeholes at the back, so that he was unable to see what was going on, that DPC 50049 then punched his head and he heard similar treatment being meted out to one of his co-defendants. 47. The similarity between these alleged events and the events alleged to have occurred on 26 August are first the use of gratuitous violence by police officers and secondly the covering of the head of those whom they were detaining. These acts were not, however, alleged to have been done by the same police officers. Indeed DPC 50049 and DPC 34311, who were alleged to have been responsible for the violence on 9 July, did not take part in the raid on 26 August. The leader of the team was, however, the same man – DSIP Chan. 48. The Judge heard the conflicting evidence of the police officers who took part in the raid on 9 July and the Appellant. That evidence did not leave her in doubt as to whether the Appellant had made the statements recorded in DPC 50049’s notebook nor as to whether those statements, and the subsequent statements made by the Appellant in the video-recorded interview were made voluntarily. Had she been fully informed as to the evidence that Mr Wong was expected to give would she, or should she, have considered that it might lead her to revise her conclusions in relation to the evidence that she had heard? I have concluded that it neither would nor should have done so. 49. The fact that gratuitous violence was, or might have been, used on the Wong brothers by two members of DSIP Chan’s team on 26 August did not bear on the likelihood that other members of that team had fabricated admissions of the Appellant on 9 July, had prevented the Appellant from having access to a lawyer and had induced him to make demonstrably false statements when taking part in the video-recorded interview. Thus Mr Wong’s evidence had no relevance to the most significant aspects of the positive case advanced by the Appellant. The matter does not, however, end there. 50. An admission that is induced by oppression should not be admitted in evidence at a trial or, if admitted, should be disregarded by the jury. The reason for this is the protection that the law gives against self-incrimination. Even though a defendant denies making the statement in question, both the judge on the voir dire and the jury at the trial must, where there is evidence that raises the issue, consider whether or not if the statement was made it was voluntary. Unless satisfied of this the judge must rule the statement inadmissible on the voir dire and the jury must be directed to disregard the statement where it has not been excluded on the voir dire[16]. 51. Thus there may be two issues in relation to a statement alleged to have been made by the defendant. First, where the defendant denies making the statement, a patent issue of whether the defendant made the statement. Secondly a latent issue – if the defendant did make the statement, may it have been induced by oppression. 52. At a trial where the defendant gives evidence denying that he made an inculpatory statement it would plainly be likely to confuse the jury if he were permitted to lead similar fact evidence of police conduct on a different occasion for the purpose of buttressing an alternative case that, if he made the statement, it was forced out of him. For this reason, a judge would normally be likely to refuse an application to adduce such evidence. Indeed, I am not aware of any case in which such an application has been made. 53. The position is not the same on the voir dire. Even though the defendant gives evidence denying making the statement in question the judge will be alive to the issue of whether, if the statement was made, it was voluntary. That is what the voir dire is all about. Defence counsel will not necessarily be inhibited from addressing the judge on the hypothesis that his client may not be telling the truth when denying making the statement. 54. In the present case Mr Ross has now made it clear why he wished to adduce Mr Wong’s evidence. This was by way of similar fact evidence to support a case that the statements alleged to have been made by the Appellant were (if made) induced by oppression. Were the contested allegations in relation to behaviour of the police during the raid on 26 August of sufficient relevance and cogency in relation to that issue to justify the admission of Mr Wong’s evidence as similar fact evidence on the voir dire? I do not consider that they were. Other than the fact that gratuitous violence was alleged to have been used on the two occasions, there were few similarities between them. First and foremost, the police officers who were alleged to have used violence on the Appellant and his co-defendant were not alleged to have used violence on Mr Wong or his brother. Indeed they were not even present on 26 August. The team had the same leader on both occasions but not all the members of the team were the same. The nature of the alleged assaults was not the same. The Appellant alleged that a hood was put on his head that prevented him seeing what was being done by the police in the flat. Mr Wong alleged that his head was covered by a blanket while he was being assaulted. 55. The judge did not elaborate on the chain of reasoning that led her to conclude that the Appellant had made the statements alleged and had done so voluntarily, but I cannot conceive that her conclusion would have been affected had she entertained evidence from Mr Wong as to what occurred on the night of August 26th. 56. The facts of this case have raised an unusual issue as to the application of the principles governing the admission of collateral evidence. I have, however, been left in no doubt that no criticism can be made of the refusal of the Judge to permit Mr Wong to give evidence on the voir dire. 	I would, accordingly, dismiss this appeal. Chief Justice Ma: 57. For the reasons contained in the judgment of Lord Phillips of Worth Matravers NPJ, this appeal is dismissed. Mr Phillip Ross, instructed by Patrick Mak & Tse, assigned by the Director of Legal Aid, for the Appellant Mr William Tam, DDPP, and Mr Ivan Cheung, PP, of the Department of Justice, for the Respondent [1] CACC 51/2011, 3 October 2013 before Hon Stock VP, Lunn JA and McWalters J. [2] Judgment 8 November 2013. [3] 4 June 2014, Mr Justice Ribeiro PJ, Mr Justice Tang PJ and Mr Justice Fok PJ. [4] O’Brien v Chief Constable of South Wales Police [2005] UKHL 26 at para 11; [2005] 2 AC 534, at 543. [5] Goldsmith v Sandilands [2002] HCA 31 at para 1, (2002) 190 ALR 370. [6] eg: in England and Wales, the Criminal Justice Act 2003 s.100; in some parts of Australia provisions under the Uniform Evidence Acts – see Goldsmith v Sandilands (supra) at para 66; in New Zealand the Evidence Act 2006 sections 37-39. [7] (2003) 6 HKCFAR 135 [8] para 52 [9] 1999/04971/Z5 (unreported: 23 March 2000) [10] [1991] 1 WLR 207 [11] See O’Brien (supra) at para 41 [12] R v Malik [2000] 2 Cr App R 8 at p 12 [13] [2010] 5 HKLRD 101. [14] per Stock V-P at para 37. [15] Para 90 [16] See HKSAR v Pang Hiu San FACC No 3 of 2014 where this area of the law is dealt with at length.