Chief Justice Cheung: 1. I agree with the judgment of Mr Justice Lam PJ. Mr Justice Ribeiro PJ: 2. I agree with the judgment of Mr Justice Lam PJ. Mr Justice Fok PJ: 3. I agree with the judgment of Mr Justice Lam PJ. Mr Justice Lam PJ: 4. In this appeal, this Court has to examine whether the restrictions set by a magistrate on cross-examination as to credit were properly imposed in light of the principles set out in HKSAR v Wong Sau Ming[1] and HKSAR v Kong Wai Lun[2]. The appellant says she had suffered a substantial and grave injustice because cross-examination was not allowed on the details of some allegations which did not form part of the prosecution case. The Appeal Committee exceptionally granted leave to appeal as the question raised by the appellant on the distinction between cross-examination on credit and on the general issue is of importance and the relevant argument was apparently less developed, and therefore not fully addressed, in the courts below. A. Background 5. The appellant was convicted by a magistrate, Mr Colin Wong, of two charges of aiding, abetting, counselling, or procuring the breach of conditions of stay by a foreign domestic helper employed by her. She was sentenced to 4 months’ imprisonment. In his Statement of Findings, the magistrate accepted the evidence of the foreign domestic helper, Ms Kamalawathi, who was the principal witness for the prosecution at the trial. 6. The helper was employed by the appellant under two consecutive contracts: the first ran from November 2012 to November 2014; the second ran from December 2014 to November 2016. Under the conditions of stay imposed by the Director of Immigration, the helper could only perform domestic duties for the appellant at a specified address in The Sea Ranch, Lantau Island. The address specified under the first contract was different from that specified under the second contract. The employment under the second contract was terminated on 8 November 2015. 7. The helper had also brought a civil claim against the appellant for compensation allegedly due in respect of work done at places other than those specified addresses. At the time of the criminal trial, the civil proceedings were still pending. 8. The prosecution case was that the appellant had instructed the helper to work at places other than the specified addresses in breach of her visa conditions. Two charges were brought against her in October 2017: one for instructions given under the first contract and another for instructions given under the second contract. Constrained by the limitation period for prosecution[3], in respect of the employment under the first contract, the appellant was only charged for the instructions given by her during the last two months (viz October and November 2014). 9. The appellant did not testify. Nor did she adduce any factual evidence at the trial. Her case, as put by her counsel, was that she did not give such instructions. Her only witness was a medical expert testifying on the onset and the impact of the mental illness of the helper who had previously suffered from schizophrenia and had recovered by the time she testified. The magistrate preferred the evidence of the medical expert called by the prosecution. 10. Under the first charge, the other places at which the helper was instructed by the appellant to work were identified in the Statement of Findings and the judgment below as House No. 11, House No. 13 and House No. 10 at The Sea Ranch on Lantau Island (“the Other Sea Ranch Houses”). The helper was instructed to clean these houses and to remove debris in House 11 which was then under renovation[4]. 11. In addition, as emerged from the evidence of the helper given under cross-examination, she was also instructed by the appellant to carry out work at a restaurant in Cheung Chau and an office in Fo Tan, Shatin (“the Non-Domestic Work”). In her examination-in-chief the helper did not refer to her working in these places. As the cross-examination progressed, it became clear that the Non-Domestic Work was not undertaken during the periods specified in the charges[5]. B. The restrictions imposed by the magistrate B1. Trial counsel’s stated purposes of the cross-examination 12. The appellant was represented by two counsel at the trial. The first trial counsel Mr Kong’s stated purpose of cross-examining on the Non-Domestic Work was to explore the credibility of the witness by reference to her civil claims (in terms of the hours of work she had undertaken each day) and the reliability of her memory in conjunction with her mental illness[6]. He also sought to cross-examine on assignments which he mistakenly believed to be correlated with work undertaken at the Other Sea Ranch Houses[7]. 13. The magistrate gave Mr Kong some leeway in such cross-examination but ruled that it was not necessary to go into the details. After further questioning of the witness, Mr Kong realized that the Non-Domestic Work was undertaken before the first charge period and there was no temporal correlation with the subject matter of the charge. Counsel then decided to move on to other topics in his cross-examination[8]. 14. Later, the second trial counsel, Mr Tse, sought to cross-examine on the Non-Domestic Work to show that the allegations were fabricated. But he did not explain to the magistrate that he had a different foundation for challenging the credit of the helper. His only ground for re-visiting the topic was that the helper’s complaint to the Immigration officer should be read as a whole. The magistrate reiterated his earlier ruling[9]. 15. The ruling was not an absolute bar and the magistrate subsequently allowed Mr Tse to ask questions concerning the work at the restaurant which purportedly overlapped with the work at the renovated house[10]. B2. The magistrate’s reasons for the restrictions 16. The magistrate disapproved the proposed testing of the witness’s memory by reference to collateral matters and he did not see any need to refer to the details of the Non-Domestic Work in order to serve counsel’s stated purposes. He therefore permitted cross-examination on the frequency and time of such work without going into details[11]. Based on counsel’s submissions, the magistrate regarded such cross-examination as solely relevant to credit and made such ruling on two grounds[12]: that such work was undertaken outside the charge periods; and that such allegations would have to be determined in the pending civil proceedings and were not properly within the ambit of the criminal case being tried. B3. The appeal to the Court of First Instance and the judge’s view on the restrictions 17. The appellant appealed against the convictions and the appeal was dismissed by D’Almada Remedios J. The arguments advanced before Her Ladyship were not as focused as those advanced before us. Leading counsel then appearing for the appellant (not Mr Corlett) submitted that the magistrate erred in not allowing questions based on the helper’s previous statements. The learned judge rejected that challenge and Mr Corlett did not rely thereon. 18. After carefully analysing the transcript in detail the learned judge concluded that the magistrate had given proper leeway to the defence to cross-examine on collateral matters. Regarding the Non-Domestic Work, she was of the view that he had only disallowed questions purely for testing the helper’s memory on general matters as opposed to specific inconsistencies[13]. 19. In respect of the pre-emption of Mr Tse’s cross-examination, the learned judge concluded that the magistrate had only required the questions to be relevant to the core issues of the charges and the credibility of the helper[14]. She also held that the magistrate had been entitled to restrict cross-examination so that it would not serve as a memory-testing exercise on matters irrelevant to the charges[15]. She concluded that there had not been any unfairness to the appellant[16]. B4. Issues in the appeal 20. The main issues in the appeal are as follows: (a) Whether the magistrate unduly restricted the defence in cross-examination on the Non-Domestic Work; (b) Whether the appellant suffered any injustice as a result of such restrictions. 21. Before addressing these issues, it is necessary to discuss the relevant legal principles in light of Mr Corlett’s submission on the lack of significance of the distinction between cross-examination on a primary issue and on credit in cases where the witness’s credibility is a core issue. C. The legal principles on cross-examination as to credit C1. The principles as discussed in Wong Sau Ming and Kong Wai Lun 22. A useful starting point is the judgment of Li CJ in HKSAR v Wong Sau Ming, supra at [23] to [26]: “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.” 23. Wong Sau Ming was a drugs case and the issue of principle arose from the cross-examination of the police officer who found the drugs on the defendant. There was a dispute on admissibility of evidence about the acquittal of a different defendant in an earlier drugs case in which the same officer had been involved and which had occurred within a few weeks of the case at hand. In such a context, the Court held that two threshold requirements had to be met before cross-examination on credit by reference to such an acquittal would be permitted: (a) The acquittal involved a finding by the court that the police officer had lied or that the court had disbelieved him; and (b) The circumstances of the earlier case were of such a kind when compared to those in the case before the court that the previous finding was not so remote in time or nature, that the finding of lying in the earlier case would materially affect the assessment of the witness’s veracity in the case at hand[17]. 24. In Wong Sau Ming, though the magistrate in the earlier case had given the benefit of doubt to the defendant, there was no finding that the police officer had lied or that he had been disbelieved. Thus, the first threshold requirement was not satisfied and the Court held that cross-examination by reference to the acquittal should not be allowed[18]. The significance of the first threshold requirement was explained at [30]: “… In acquitting, the court may not have found that the witness had lied. Unless in acquitting, the court had found that the witness had lied (or, which amounts to the same thing, the court had disbelieved the witness), the acquittal could not properly be regarded as relevant to the veracity of the witness in the instant case. It would not have a sufficiently material impact on the court’s assessment of his veracity.” 25. The Court further observed that had the first requirement been fulfilled, the second threshold requirement could have been met in that particular case[19]. But cross-examination by reference to an acquittal would only be permitted when both threshold requirements were met. 26. Subsequently, in HKSAR v Kong Wai Lun, another drugs case, the defendant had given a statement to a police officer the admissibility of which was challenged on the ground of police violence against him. It was alleged on appeal that the trial judge had wrongly refused to permit the defence to adduce evidence in the voir dire from another person allegedly assaulted by the same team of police officers several months after the arrest of the defendant on an occasion unconnected with the offence with which the latter was charged. The police officer had been cross-examined and he denied the allegation of police impropriety on that occasion. Not surprisingly, the appeal was dismissed. 27. Lord Phillips of Worth Matravers NPJ identified two applicable common law principles at [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. 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 …” 28. In the application of these basic principles, a distinction is drawn between primary issues and collateral issues, see [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.” 29. After referring to Wong Sau Ming, His Lordship further summarized at [34] the position governing cross-examination on credit: “… 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. 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.” 30. On the facts of Kong Wai Lun, Lord Phillips agreed with the Court of Appeal that the evidence of purported police violence on the other occasion had little bearing on the credibility of the police officers and the finality rule barred the admission of the evidence the defence proposed to call at the voir dire[20]. 31. At [43], Lord Phillips reiterated that the procedure laid down in Wong Sau Ming should be followed when counsel applies to adduce evidence of events unconnected with those giving rise to the prosecution, including evidence relevant to credit only. The relevant witness statement should be placed before the trial judge to enable him to assess the probative value of the proposed evidence. His Lordship stressed: “… 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 …” C2. The discretion to permit cross-examination on credit based on previous misconduct 32. As stated in these authorities, the rationale for permitting cross-examination on credit stems from the materiality of a line of questioning on the assessment of a witness’s veracity. Since the ultimate benchmark is relevance which is a matter of degree, it would be unwise and indeed impossible to lay down hard and fast rules. But it is useful to highlight the requirement of laying a proper foundation for casting an imputation of misconduct against a witness. 33. Recently, the Judicial Committee of the Privy Council examined the common law principles governing cross-examination of a witness as to credit in Clarke v The State[21]. Lord Lloyd-Jones succinctly summed up the position as follows at [40]: “At common law, therefore, the judge had a discretion to permit cross- examination as to credit. In exercising that discretion he was required to have regard to whether such questions would seriously affect the jury’s view of the credibility of the witness, to whether the misconduct relied upon had a solid foundation, to the fairness to the witness of permitting such cross-examination and to whether such cross-examination would be a distraction from the real issues in the case. An appellate court may not interfere with the exercise of such a discretion unless it is clearly wrong or wrong in principle.” 34. The need for having a solid foundation for an imputation of misconduct was explained in Persad and Jairam v The State[22] which was cited at [39] of Clarke: “Behind all this is the necessity of securing a fair trial for the accused person consistently with fairness to a witness. It is not fair for a witness to be assailed with unproven allegations of misconduct or with mere suspicions of past malpractice. Nor is it acceptable for the time of the court to be taken up with matters extrinsic to the case in hand nor for the jury to be distracted from the issue before them by inquiries into uncertain and unresolved issues about the earlier conduct of a witness. The investigation of a witness’s reliability in the course of cross-examination must be kept within bounds. It cannot be allowed to degenerate into a ranging and speculative inquiry into any or all of the occasions on which the witness has given evidence in the past.” 35. The threshold requirements set by Li CJ in Wong Sau Ming for cross-examination on credit based on previous acquittals can be regarded as a specific formulation of a solid foundation in such context. 36. The suggestion that a witness told lies on a previous occasion is an imputation of misconduct[23]. Whilst the immediate context in Wong Sau Ming was a police officer lying to the court, the observation of Lord Phillips in Kong Wai Lun was a general one. In the context of cross-examination on credit, no distinction can be drawn between an imputation levelled against a police officer and that levelled against a civilian witness. As far as the requirement of a solid foundation is concerned, there is no difference between casting an imputation of lies told in court and lies told to a public officer for law enforcement purposes. If a cross-examiner does not have a solid foundation for casting the imputation, the question would have no relevance to the assessment of the veracity of the witness and should not be allowed. C3. The distinction between primary issue and credit 37. Whilst judges at times find the distinction between cross-examination on primary issues and cross-examination as to credit difficult to draw, it is recognized that such distinction is important and necessary in order to confine the ambit of a trial within proper limits and to ensure that the trial is focused on the central issues instead of being side-tracked by collateral issues. The principles governing cross-examination on credit and the finality rule are premised on such distinction. Both Li CJ in Wong Sau Ming[24] and Lord Phillips in Kong Wai Lun [25] upheld this distinction as a matter of common law in Hong Kong. 38. In the present appeal, Mr Corlett invited us to draw a further distinction. Accepting that cross-examination as to the general credit of a witness would be governed by the principles discussed above, counsel submitted that questions relevant to the witness’s credibility on matters sufficiently closely related to the subject matter of the indictment would not. In the latter situation, counsel said the correct approach was that adopted in R v Funderburk[26]and HKSAR v Cheung Hok Man[27]. In Cheung Hok Man, Chu J (as Chu JA then was) held at [32]: “… The legal principles laid down by these authorities[28] were: as sexual acts in sexual cases usually take place in private, the evidence would basically be limited to that of the complainants’, and assessing their credibility thus lies as a core question in those cases. Consequently, there is in effect no line drawn between issues relevant to the credibility of a witness and questions relevant to an issue in a case; evidence which has bearing on the credibility of the witness would have bearing on the matters in dispute in the case as well. Hence, the court should allow calling evidence relevant to the credibility of the complainants, because the evidence may cause the jury to come to a different view of their testimonies.” 39. Mr Corlett also relied on the following part of the judgment in Funderburk[29]: “… It seems to us that on the way the prosecution presented the evidence the challenge to the loss of virginity was a challenge that not only did the jury deserve to know about on the basis that it might have affected their view on the central question of credit, but was sufficiently closely related to the subject matter of the indictment for justice to require investigation for the basis of such a challenge.” 40. Whilst the restriction on cross-examination as to credit should be applied with flexibility, I cannot accept that once it is demonstrated that the credibility of a witness is of crucial importance the court should give free rein to counsel in the cross-examination on credit and the calling of evidence in rebuttal. Nor do I accept Mr Corlett’s further distinction between cross-examination on general credit and cross-examination on credibility regarding matters closely related to the subject matter of the charge. 41. In Wong Sau Ming and Kong Wai Lun this Court firmly maintained the distinction between cross-examination on primary issues and cross-examination on credit notwithstanding that the evidence of the police officers in both cases was of crucial importance to the prosecution case. 42. On a proper analysis, the proposed cross-examination in Cheung Hok Man and Funderburk clearly related to the general issues in the cases rather than solely to credit. 43. In Cheung Hok Man, the issue was whether sexual intercourse had taken place. It was part of the complainant’s evidence that after the alleged rape she headed back home. On the way, she worried about getting pregnant and purchased “morning after pills”. She denied having met her god-brother in the course of that journey. The evidence of the god-brother (whom the trial judge refused to allow the defence to call) could cast doubt on the complainant’s evidence of purchasing contraceptives immediately after the alleged rape. Thus it was relevant to the issue of whether sexual intercourse had taken place. 44. Likewise, in Funderburk, the proposed cross-examination was directed at challenging the complainant’s evidence-in-chief that she was a virgin prior to the alleged rape, the defence case being that she had either transposed experiences which she had had with others or fantasised her experience with the appellant. Henry J (as he then was) held that the rules of evidence designed to promote justice should not be applied to preclude such cross-examination when the complainant’s account of loss of virginity would be the most vivid picture in the minds of the jury[30]. Thus, emphasis was placed on the way in which the prosecution had presented the evidence in the dicta cited by Mr Corlett. 45. On the other hand, in cases where the cross-examination is relevant only to a challenge on the credibility of a witness, the usual restriction and the finality rule should be applied even when the evidence of the witness is of crucial importance to the prosecution case. At the same time, whilst it is essential to prevent the primary issues becoming obfuscated as a result of unrestricted admission of evidence on collateral issues, a trial judge should pay regard to fairness and justice in the particular circumstances of the case. When it is demonstrated that the probative value of a line of cross-examination on credit clearly outweighs any potential for confusion or obfuscation by the introduction of collateral issues, the discretion should be exercised in favour of permitting cross-examination. 46. In making the abovementioned assessment, the proximity or remoteness of the topic for cross-examination in connection with the subject matter of the charge is relevant. But it is also relevant to consider whether there is a solid foundation for casting an imputation on the credibility of a witness by reference to that topic. This approach is reflected in the two threshold requirements laid down in Wong Sau Ming in the context of cross-examination by reference to a previous acquittal. C4. The duty to explain the relevance and to lay proper foundation 47. Since the extent to which cross-examination should be allowed on credit is discretionary, one must have regard to the arguments and the materials that had been put before the trial judge in assessing whether an appellate court should intervene. 48. In the fulfilment of the duty to provide the court with all material information discussed in Kong Wai Lun, a cross-examiner should clearly explain the relevance and basis of the proposed cross-examination on credit. Before casting an imputation of misconduct against the witness, it is also necessary to be able to demonstrate that there is a solid foundation for the same. D. The magistrate had exercised his discretion properly D1. Mr Corlett’s arguments in this Court 49. Mr Corlett submitted that the cross-examination would have been aimed at showing that the helper had lied to the Immigration officer in respect of the Non-Domestic Work. Had that been demonstrated, the court would have found it difficult to attach weight to her evidence in respect of matters which occurred within the charge periods as those allegations formed part of the same story. Counsel also said it was easier to rebut the Non-Domestic Work allegations as compared with the helper’s allegations of working in the Other Sea Ranch Houses which were vacant. 50. In the printed case of the appellant[31], Mr Corlett provided rather vague information on how the appellant intended to show that the Non-Domestic Work allegations were a fabrication. In essence, it would have involved cross-examination of the helper by open questions “to elicit as much (fabricated) detail as possible” followed by calling witnesses to rebut the same. No witness statement has ever been produced though counsel suggested that the witnesses would testify that they had never seen the helper working at the restaurant and the office. A witness would also say that her evidence that the restaurant also operated as a hotel could not be true as it did not have the requisite licence. D2. The arguments were not advanced before the magistrate 51. These were not the same arguments as those put before the magistrate. As we have seen, trial counsel had explained the purposes of cross-examination to the magistrate differently. 52. Though Mr Tse had submitted to the magistrate that the helper’s complaint to the Immigration officer had to be treated as a whole, he did not contend (as Mr Corlett now submitted before us) that cross-examination on the Non-Domestic Work would be cross-examination on the facts in issue as it was closely related to the subject matter of the charges as opposed to mere cross-examination on credit. 53. Further, Mr Tse did not inform the magistrate of the basis on which he suggested that the allegations were fabricated. He gave no indication that the defence intended to call witnesses to rebut such allegations and did not provide any outline of the evidence of these witnesses. Trial counsel had ample opportunities to put to the helper that her evidence on the Non-Domestic Work was a complete fabrication. Yet this was not done. 54. It is of no avail to the appellant that a couple of days after the ruling Mr Kong informed the magistrate that the defence decided not to call witnesses about events outside the charge period. Apart from the obvious fact that this information was not provided to the magistrate before the ruling, he was not told what such evidence was and what purpose the evidence was supposed to serve. The stark reality was that the defence did not attempt to justify the aborted cross-examination by reference to the potential evidence of these witnesses. 55. Since trial counsel had not properly explained the need for questioning on the Non-Domestic Work in detail and had failed to lay a solid foundation for suggesting the helper was telling lies, the magistrate was entitled to come to the view, as he did, that the cross-examination which he had already allowed on the frequency and time of the Non-Domestic Work was enough to serve the stated purposes of the defence. D3. No ground for interference with the exercise of the discretion 56. We were given no explanation for the magistrate not being informed of the plan of the defence as it is now canvassed before us. If this had been the plan all along, it is difficult to understand why Mr Kong explained the purposes of his cross-examination in the way he did. It is also strange that Mr Tse did not disclose such plan to the magistrate in his efforts to have the ruling re-visited. 57. Since the relevant information had not been provided to the magistrate and there is no good reason for not doing so, it cannot be said that the magistrate was in error in setting the restrictions on cross-examination in the way he did. He was correct in holding the view that the disputes over the Non-Domestic Work were not issues which he had to determine in the criminal trial and the proposed cross-examination was solely on credit. Whilst the fact that an issue would be relevant in the civil case cannot by itself be a good reason for denying a relevant line of cross-examination in the criminal trial, he was entitled to take the view that such disputes would have to be resolved by a trial of collateral issues in the criminal trial as counsel had not suggested to him that the defence could call unequivocal rebuttal evidence on it. 58. In the circumstances, there is no reason for an appellate court to interfere with the magistrate’s exercise of discretion. The appeal can be dismissed on this ground alone. E. Lack of a solid foundation for casting an imputation E1. The proposed cross-examination is only relevant to credit 59. In any event, the magistrate had allowed counsel to explore the connection between the instructions regarding the Non-Domestic Work and the work undertaken at the Other Sea Ranch Houses. The instructions were given at different times and the work was performed at different places. The nature of the work was different. In such circumstances, the mere inclusion of the Non-Domestic Work in the complaint does not mean that it had any bearing on the subject matter of the charges. 60. Even on Mr Corlett’s own argument, the only possible relevance of the cross-examination was on credit: if the court were to find that the helper had lied to the Immigration officer on the Non-Domestic Work, it would taint her credibility in respect of her evidence on the subject matter of the charges. The present case is clearly distinguishable from the situations in Cheung Hok Man and Funderburk. 61. In contrast, had the defence deployed the strategy outlined by Mr Corlett with regard to the subject matter of the charges, it would not be subject to the restriction on cross-examination as to credit. The contractor and his workers undertaking the renovation work at House 11 could have testified on the alleged removal of debris by the helper. During the second contract, the helper said she lived and worked in the home of the appellant’s brother at the specified address whilst the appellant lived elsewhere at House 11. On the other hand, the defence case as put by counsel was that she lived with the appellant, not the brother. The brother and other members of his household could have testified to contradict the helper’s allegation that she had lived with them. However, the defence did not take such course at the trial. 62. In light of the submissions of Mr Corlett (but not those advanced before the magistrate), the appellant could have made out a case for testing the credit of the helper by reference to the allegations on the Non-Domestic Work provided there was a solid foundation for casting the imputation that she had deliberately lied to the Immigration officer. In the absence of any proper basis for such an imputation, even if there were inaccuracies in those allegations, they could not have been material to the assessment of the helper’s veracity in the evidence on the subject matter of the charges. E2. No solid foundation for imputing that the helper had lied to the Immigration Officer 63. There had not been any previous finding by any court or tribunal impugning the helper’s credibility over her allegations on the Non-Domestic Work. It is not suggested by Mr Corlett that the defence could show that these allegations were fabricated simply by cross-examining the helper. 64. Lack of witness statements aside, the rebuttal evidence as outlined by Mr Corlett would not unequivocally establish that the helper was untruthful. The lack of licence for the “hotel” is neither here nor there as the helper testified that she had no knowledge as to its business operation[32]. If the proposed evidence that the helper had not been seen working at the office were adduced at the trial, the magistrate would have had to conduct a trial on these allegations in order to assess whether the helper had worked there in the absence of the rebuttal witnesses; whether she or they were to be believed; and if the evidence of such witnesses were preferred, whether the helper had deliberately lied to the Immigration officer. As Lord Phillips said in Kong Wai Lun[33]: “… 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.” 65. If the rebuttal evidence could not have been called, it is unlikely that the appellant would have gained much mileage from cross-examining on the details of the Non-Domestic Work. 66. The other purpose put forward by Mr Corlett for the further cross-examination, viz to elicit more details from the helper so that there would be more scope for rebuttal, cannot be a valid ground for allowing further cross-examination on collateral issues. This smacks of objectionable fishing which has no place in the proper cross-examination on credit. E3. Application of the finality rule does not result in unfairness 67. As it had not been demonstrated that the probative value of the proposed line of cross-examination on the details of the Non-Domestic Work clearly outweighed any potential for confusion or obfuscation by the introduction of such collateral issues, the restrictions imposed by the magistrate did not give rise to any unfairness. 68. The restrictions set by the magistrate did not give rise to any substantial and grave injustice. I would dismiss the appeal accordingly. Lord Hodge NPJ: 69. I agree with the judgment of Mr Justice Lam PJ. Chief Justice Cheung: 70. Accordingly, the Court unanimously dismisses the appeal. Mr Marc Corlett and Mr Marco S P Tse, instructed by S K Wong & Co, for the appellant Mr David Chan, SADPP and Ms Laura Liu, SPP, of the Department of Justice, for the respondent [1] (2003) 6 HKCFAR 135. [2] (2015) 18 HKCFAR 7. [3] Section 46(2) of the Immigration Ordinance Cap 115 sets a 3-year limitation period for prosecution of offences under the ordinance. [4] Transcript p.45K to Q; p.67K to N. The page references in these footnotes are the pagination at Part B of the Appeal Bundles. [5] Transcript p.30A to 31R. She had already said so on Day 1 of her evidence, see Transcript p.2P to 3J. For reason unknown to us, that seems to have escaped counsel’s attention when he suggested that some of those assignments were within the charged period at Transcript p.25B. [6] Transcript p.19N and 20A to D. [7] Transcript p.25A to D. [8] Transcript p.31Q. [9] Transcript p.48A to 50H; p.56G to K. [10] Transcript p.50R to 52D; p.55K to 56U. [11] Transcript p.22H to M; p.25E to O; p.27L to 28N. [12] Transcript p.48I to L; p.49U to 50F. [13] CFI Judgment of 17 May 2021 at [37] to [41]. [14] CFI Judgment of 17 May 2021 at [44] to [46]. [15] CFI Judgment of 17 May 2021 at [47]. [16] CFI Judgment of 17 May 2021 at [51]. [17] (2003) 6 HKCFAR 135 at [29] to [32]. [18] (2003) 6 HKCFAR 135 at [59] to [60]. [19] (2003) 6 HKCFAR 135 at [61]. [20] (2015) 18 HKCFAR 7 at [40] and [41]. Lord Phillips also considered the matter from the angle of similar fact evidence, which is not relevant for present purposes. [21] [2021] UKPC 16 at [37] to [40]. It was an appeal from Trinidad and Tobago. [22] [2001] UKPC 2 at [16]. It was also an appeal from Trinidad and Tobago. The judgment was delivered by Lord Clyde. [23] See Wong Sau Ming at [46] and Kong Wai Lun at [34]. [24] See [25] and [26] of Wong Sau Ming. [25] See [28] of Kong Wai Lun. [26] (1990) 90 Cr App R 466. [27] [2011] 3 HKLRD 810. [28] The authorities were R v Funderburk (1990) 90 Cr App R 466; R v Gibson [1993] Crim LR 453; R v Nagrecha [1997] 2 Cr App R 401 and Tiwari v The State [2002] UKPC 29. [29] (1990) 90 Cr App R 466 at p.476. [30] (1990) 90 Cr App R 466 at p.475 and 477. [31] Paras 52 to 54 of the appellant’s printed case. [32] Transcript at p.42S to 43N. [33] (2015) 18 HKCFAR 7 at [34].