1. The Appellant was charged with two counts of aiding, abetting, counselling, or procuring the breach of conditions of stay by a foreign domestic helper employed by her. The helper was employed under two consecutive contracts: the first ran from November 2012 to November 2014; the second from December 2014 to November 2016. The prosecution case was that the Appellant instructed the helper to work at places other than the addresses specified under the contracts in breach of her visa conditions (the “Non-Contractual Work”). Due to the 3-year limitation period under section 46(2) of the Immigration Ordinance (Cap. 115), the prosecution did not rely on the Non-Contractual Work allegedly done before October 2014 (the “Pre-Charge Period”). 2. Apart from the criminal proceedings, the helper had also brought a civil claim for compensation in respect of the Non-Contractual Work (the “Civil Claim”). 3. At trial, the Appellant’s counsel sought to cross-examine the helper on the allegations she made in her statement to the Immigration officer in respect of the Non-Contractual Work done in the Pre-Charge Period, in particular in respect of work undertaken at a restaurant in Cheung Chau and an office in Fo Tan (the “Non-Domestic Work”). The stated purposes were to explore her credibility and the reliability of her memory. The magistrate held that these questions were relevant to credit only, not to the primary issue of the trial. Therefore, although he permitted cross-examination on the frequency and time of the Non-Domestic Work, he did not permit questions going into the details. After considering the evidence, he convicted the Appellant of both counts. 4. On appeal, the Appellant argued that the restrictions imposed by the magistrate had deprived her of a fair trial. The Court of First Instance dismissed the appeal and held that the magistrate was right to restrict cross-examination so that it would not serve as a memory-testing exercise on collateral issues. The distinction between cross-examination on primary issue and credit 5. Before this Court, the Appellant contended that, where the witness’s credibility is a core issue of the trial, there is no distinction between cross-examination on a primary issue and on credit. Thus, defence counsel should have been permitted to conduct its cross-examination without any restrictions. This argument was rejected by the Court. There is a distinction between a primary issue, i.e. whether an event on which the prosecution relies in fact occurred, and a collateral issue, i.e. the reliability of evidence proving that a primary issue did or did not occur. The issue of credit is a collateral issue. Such distinction is important and necessary in order to confine the ambit of a trial within proper limits. 6. The extent to which cross-examination on credit should be allowed is subject to the trial judge’s discretion. The discretion should be exercised in favour of permitting cross-examination imputing misconduct when the defence demonstrates that the probative value of such cross-examination clearly outweighs any potential for confusion by the introduction of collateral issues. In making this assessment, two matters are relevant. First, the proximity of the topic for cross-examination with the subject matter of the charge. Secondly, whether there is a solid foundation for casting imputation of misconduct against a witness by reference to that topic. Defence counsel has a duty to explain these matters to the judge in order for him to exercise his discretion properly. Thus, all relevant materials, including the relevant witness statements, should be placed before the judge. The magistrate had exercised his discretion properly 7. Before this Court, the Appellant contended that cross-examination would have been aimed at showing the helper’s statement on the Non-Domestic Work was fabrication. This would be achieved by putting open questions to the helper, followed by calling witnesses who would testify that the helper had never worked at the relevant places. However, this Court observed that these were not the same arguments as those put before the magistrate by trial counsel. They did not explain that the proposed cross-examination was closely related to the subject matter of the charges, as opposed to credit only. Also, they neither informed the magistrate of the basis for saying that the helper had fabricated the allegations, nor of their plan to call witnesses to rebut such allegations. Since trial counsel had not properly explained the need for questioning on the Non-Domestic Work in detail, the magistrate was entitled to set the restrictions on cross-examination in the way he did. There was no solid foundation for casting an imputation 8. In any event, in the context of the present case the cross-examination was only relevant on the credibility of the helper. 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. The rebuttal evidence as outlined by the Appellant before this Court would not unequivocally establish that the helper was untruthful. As there was no solid foundation for imputing that the helper had previously lied in her statement, the Appellant would be bound by the finality rule. Thus, the Appellant did not suffer any substantial or grave injustice. DISPOSITION: 9. Accordingly, the Court unanimously dismissed the appeal.