The Court: 1. These two appeals, heard together, raise overlapping issues concerning the offences of unlawful assembly and riot under sections 18 and 19 of the Public Order Ordinance (“POO”).[1] 2. The appellant Lo Kin Man (“Lo”) was convicted after trial before A Pang J and a jury[2] of the offence of riot contrary to section 19 of the POO involving an occurrence of public disorder in Portland Street, Mongkok, on 8 and 9 February 2016. His appeal to the Court of Appeal was dismissed.[3] Leave to appeal to this Court was granted by the Appeal Committee[4] in respect of the questions of law and the “substantial and grave injustice” ground set out in Annex 1 to this Judgment. We shall refer to the proceedings leading to the present appeal as “the Lo Case”. 3. In relation to the second appeal, Tong Wai Hung (“Tong”) was charged alongside two other defendants with unlawful assembly and riot under POO sections 18 and 19 in connection with a riot which occurred some three years later amidst the widespread and serious social unrest which has been described in Kwok Wing Hang v Chief Executive in Council.[5] The riot in question took place on 28 July 2019 at Des Voeux Road West. He was acquitted after trial before HH Judge Anthony Kwok in the District Court.[6] This prompted the Secretary for Justice to refer two questions of law to the Court of Appeal for its opinion pursuant to section 81D of the Criminal Procedure Ordinance (“CPO”).[7] Having been provided with its opinion,[8] Tong applied for certification of the two abovementioned questions for leave to appeal to this Court. The Court of Appeal was aware of the grant of leave in the Lo Case and, noting the overlapping issues, granted certification.[9] By consent, the Appeal Committee granted leave to appeal in respect of the said questions which are set out in Annex 2 to this judgment. The proceedings leading to the present appeal are referred to as “the Tong Case”. 4. The questions raised in the two Annexes concern a proper understanding of the structure and elements of the offences created by sections 18 and 19 and their relationship with certain common law doctrines. In particular, issues arise as to (i) the existence and nature of a requirement (if any) for proof of a “common purpose” shared by the defendant and other persons assembled;[10] (ii) the applicability of the doctrine of joint enterprise to the two statutory offences and whether that doctrine enables liability to be established without the defendant being present at the scene;[11] and (iii) whether a defendant can be found guilty under sections 18 and 19 on the basis of “encouragement through [the defendant’s] presence”, without committing acts specifically prohibited by those sections.[12] Under the “substantial and grave injustice” heading, a question is raised as to the consequences of the indictment having made no mention of any participants in the riot other than the named co-defendants who were not convicted after trial together with the defendant.[13] A. The structure and elements of the offences under sections 18 and 19 A.1 The sections 5. A textual examination of the statutory offences is the appropriate starting-point. Indeed, as the relevant provisions form part of a codifying Ordinance, the primary emphasis should be on giving effect to their terms, properly construed, rather than delving too extensively into pre-existing common law authority. As Lord Herschell explained in The Governor and Company of the Bank of England v Vagliano Brothers:[14] “I think the proper course is in the first instance to examine the language of the statute and to ask what is its natural meaning, uninfluenced by any considerations derived from the previous state of the law, and not to start with inquiring how the law previously stood, and then, assuming that it was probably intended to leave it unaltered, to see if the words of the enactment will bear an interpretation in conformity with this view. If a statute, intended to embody in a code a particular branch of the law, is to be treated in this fashion, it appears to me that its utility will be almost entirely destroyed, and the very object with which it was enacted will be frustrated. The purpose of such a statute surely was that on any point specifically dealt with by it, the law should be ascertained by interpreting the language used instead of, as before, by roaming over a vast number of authorities in order to discover what the law was, extracting it by a minute critical examination of the prior decisions, dependent upon a knowledge of the exact effect even of an obsolete proceeding such as a demurrer to evidence.” 6. POO section 18 (unlawful assembly) provides as follows: “(1) When 3 or more persons, assembled together, conduct themselves in a disorderly, intimidating, insulting or provocative manner intended or likely to cause any person reasonably to fear that the persons so assembled will commit a breach of the peace, or will by such conduct provoke other persons to commit a breach of the peace, they are an unlawful assembly. (2) It is immaterial that the original assembly was lawful if being assembled, they conduct themselves in such a manner as aforesaid. (3) Any person who takes part in an assembly which is an unlawful assembly by virtue of subsection (1) shall be guilty of the offence of unlawful assembly and shall be liable – (a) on conviction on indictment, to imprisonment for 5 years; and (b) on summary conviction, to a fine at level 2 and to imprisonment for 3 years.” 7. And section 19 (riot) states: “(1) When any person taking part in an assembly which is an unlawful assembly by virtue of section 18(1) commits a breach of the peace, the assembly is a riot and the persons assembled are riotously assembled. (2) Any person who takes part in a riot shall be guilty of the offence of riot and shall be liable- (a) on conviction on indictment, to imprisonment for 10 years; and (b) on summary conviction, to a fine at level 2 and to imprisonment for 5 years.” 8. As was done in HKSAR v Leung Chung Hang Sixtus,[15] it is convenient for the purposes of exposition to divide up and number (in square brackets) the elements making up the two offences as follows: Unlawful assembly (section 18) [1] When 3 or more persons, [2] assembled together, [3] conduct themselves in a disorderly, intimidating, insulting or provocative manner [4] intended or likely to cause any person reasonably to fear that the persons so assembled will commit a breach of the peace, or will by such conduct provoke other persons to commit a breach of the peace, [5] they are an unlawful assembly. [section 18(1)] [6] It is immaterial that the original assembly was lawful if being assembled, they conduct themselves in such a manner as aforesaid. [section 18(2)] [7] Any person who takes part in an assembly which is an unlawful assembly by virtue of subsection (1) shall be guilty of the offence of unlawful assembly ... [section 18(3)] Riot (section 19) [8] When any person taking part in an assembly which is an unlawful assembly by virtue of section 18(1) [9] commits a breach of the peace, [10] the assembly is a riot and the persons assembled are riotously assembled. [section 19(1)] [11] Any person who takes part in a riot shall be guilty of the offence of riot ... [section 19(2)] A.2 Unlawful assembly 9. Elements [1] to [4] are the constituent elements of an unlawful assembly. Where they are established, the assembly is (as [5] declares) an unlawful assembly. Element [1] requires there to be 3 or more persons [2] assembled together, who conduct themselves in the disorderly manner specified in [3], with the intended or likely consequences stated in [4]. Those persons will be referred to as “the constituent offenders” and their conduct specified in [3] and [4] as “the prohibited conduct”. The true construction of element [4] is dealt with in detail in HKSAR v Leung Chung Hang Sixtus.[16] Notably, the “likely” limb is an aspect of the actus reus requiring the objectionable conduct, objectively assessed, to be likely to produce the reasonable fear of a breach of the peace specified.[17] 10. Element [6] reflects the scheme of graduated liability. An assembly might start off as lawful, then turn into an unlawful assembly and then become a riot. The time such a transformation may take will vary according to the circumstances. An unlawful assembly could develop almost immediately into a riot. 11. Element [7] is the offence-creating provision. Any person who “takes part” in an assembly which is an unlawful assembly commits the section 18 offence. The actus reus is “taking part”. This may or may not involve the same acts as, and should not be confused with, the prohibited conduct of the constituent offenders referred to in [3] and [4]. 12. If the defendant was one of the constituent offenders, by engaging in the prohibited conduct, he or she will (along with other constituent offenders) have taken part in the unlawful assembly that they will together have brought into being. But the defendant need not be one of the constituent offenders and can “take part” by joining in later. This is clear from element [7] which provides that the offence is committed by any person who takes part in the unlawful assembly. The submissions of Ms Gladys Li SC[18] to the contrary are rejected. 13. What then constitutes “taking part” in the unlawful assembly? What acts must the defendant perform? The sections do not spell out the meaning of those words. As a matter of textual analysis, it is implicit that if the defendant is one of the constituent offenders whose conduct falls within [3] and [4] he or she would “take part” since it is by such acts that the unlawful assembly is established, being of the essence of the offence. And if the defendant was not among the constituent offenders, but joined in and similarly did acts prohibited by [3] and [4], he or she would also be found to have “taken part”. 14. However, the offence is not confined to such conduct. As a matter of language, “taking part” is a broad expression. In our view, those words also embrace conduct which does not itself fall within [3] and [4] but which involves the defendant facilitating, assisting or encouraging the performance of such conduct by others participating in the assembly. Such conduct would traditionally give rise to accessorial liability but, by offering such facilitation, assistance or encouragement, the defendant acts in furtherance of the prohibited conduct and may thus also be regarded as “taking part” in the unlawful assembly. In so doing, he or she may attract liability either as a principal offender under section 18 or an aider and abettor. 15. An important feature which emerges from the statutory language is that unlawful assembly is what might be called a “participatory offence”. Thus, the offence requires the constituent offenders who are “assembled together” to “conduct themselves” in the prohibited manner so that the intended or likely fear of a breach of the peace is fear of what “the persons so assembled” will do. Element [6] draws the line between lawful and unlawful assemblies by reference to persons who “being assembled” engage in the prohibited conduct. The offence is committed by someone “taking part” in the unlawful assembly. 16. The defendant must therefore be shown not merely to have been engaging in disorderly conduct alone, but to have acted as part of an assembly with others who were also participants. The offence is “participatory” in that sense. Such participation is a requirement recognised by Lam JA (as Lam PJ then was) in SJ v Leung Kwok Wah,[19] holding that the defendant’s conduct has to be assessed to see if a sufficient nexus with other participants exists to justify regarding them as acting together.[20] His Lordship held that their conduct has to justify the inference that they had what he called “a common purpose in acting in the statutorily prescribed manner;”[21] ie, a shared objective of engaging in the ‘prohibited conduct’ forming elements [3] and [4]. 17. The defendant must accordingly intend to take part in, that is, become part of, the unlawful assembly, being aware of the related conduct of other participants and intending, while assembled together with them, to engage in or act in furtherance of the prohibited conduct. The defendant must, in other words, have what we will call a “participatory intent”. 18. It follows (leaving aside for now accessory and inchoate liability (especially regarding liability for conspiracy and incitement) that may be incurred by a person who is absent[22]), that to be guilty under section 18 as a principal offender, the defendant has to be present as part of the assembly, together with other participants. A.3 Riot 19. The offence of riot builds on that of unlawful assembly. Its starting-point is that an unlawful assembly exists, ie, that elements [1] to [5] are established. Element [8] specifies that when any person taking part in the unlawful assembly [9] commits a breach of the peace, the assembly [10] becomes a riot and the people assembled are riotously assembled. The actus reus of the offence of riot under section 19 is committed [11] when any person “takes part” in the riot. 20. Thus, as with unlawful assembly, the offence of riot has its initial constituent elements which are distinct from the actus reus of “taking part in a riot”. Any person taking part in an unlawful assembly may turn that assembly into a riot by committing a breach of the peace. That person does not have to be one of the constituent offenders who initially constituted the unlawful assembly, but he or she has to be a participant in the unlawful assembly. Any person who “takes part” in a riot which has come into existence commits the offence of riot [11]. Such a person does not have to be the person responsible for the initial, constituent breach of the peace. Neither does he or she have to have taken part in the unlawful assembly prior to it turning into a riot. Any person may take part by joining in after the unlawful assembly has become a riot. 21. Mirroring the analysis regarding unlawful assembly, the defendant’s conduct amounting to “taking part” in the riot must involve acts in furtherance of the riot. It must involve committing breaches of the peace or doing acts facilitating, assisting or encouraging breaches of the peace by others, making the defendant guilty as a principal or as an aider and abettor. We will return below[23] to consider what committing a breach of the peace entails. 22. The offence of riot is also participatory in nature. The constituent act involves a breach of the peace by a person who was taking part in an unlawful assembly. When that occurs, the “persons assembled” are declared by element [10] to be “riotously assembled”. The person who first committed a breach of the peace would thus be taking part in an assembly which has become a riotous assembly. Any other person who commits the offence by “taking part” in the riot, does so as part of the “riotous assembly”. Such person must have a participatory intent, intending to take part in the riot by committing, or acting in furtherance of, breaches of the peace together with other participants engaged in riotous activities. 23. As with unlawful assembly, it follows that liability for the offence of riot as a principal implicitly requires the defendant to be present and acting with the others riotously assembled. Again, this is subject to what is said about accessorial and inchoate liability incurred by persons who are absent, discussed below.[24] 24. It should be noted that the Court of Appeal in the Lo Case[25] and Poon CJHC writing for the Court in the Tong Case[26] omitted reference to the offence-creating, “taking part” provisions when setting out sections 18 and 19. This failure to focus on “taking part” as the actus reus of the two offences appears to have had an important influence on their approach to joint enterprise to which we shall return.[27] B. “Common purpose” 25. In the Lo Case, the appellant’s propositions on “common purpose”, reflected in Annex 1, Questions 1a-1d, may be summarised as follows: (a) The offences of unlawful assembly and riot were common law offences. At common law, it was necessary for the prosecution to prove against the defendant all the elements of the unlawful assembly which then became a riot. These included the prohibited disorderly conduct and a shared intent to engage in such conduct (what we have called a “participatory intent”). (b) Additionally, so the argument runs, it was necessary to prove that the assembled persons had a “common purpose” which they jointly intended to pursue, such as to wreck a dinner or cause a work stoppage.[28] Such a purpose may be referred to as an “extraneous common purpose” which is distinct from and goes beyond the participatory intent to engage in the prohibited conduct or to commit breaches of the peace. It is “extraneous” in that it is not a purpose which relates to any element of the offences but involves an external objective motivating the offenders. Lo’s submission is that the common law required such an extraneous purpose, which might or might not be lawful in itself, to be shared in common by those taking part in the unlawful assembly or riot. (c) It is argued that an extraneous common purpose continues to be required by the POO as a necessary element of both unlawful assembly and riot. The Judge, it is said, erred in failing to recognise, and give directions on, this additional element. 26. The prosecution’s position, adopted by the Judge in her directions to the jury and upheld by the Court of Appeal,[29] is that the prosecution has to prove that the defendant, assembled together with other persons, acted with a participatory intent, intending together with others assembled to behave in the prohibited manner or to commit or further the commission of the prohibited acts or breaches of the peace; but that there is no extraneous common purpose to be proved. 27. The competing arguments raise two questions: (i) What was the position regarding “common purpose” at common law? (ii) To what extent is the common law position still applicable after passage of the POO in 1967? B.1 Common purpose at common law 28. The common law authorities were in some disarray. Some, for instance, referred to the persons assembled having an extraneous common purpose but without necessarily suggesting that such a purpose was an essential ingredient of the offences. Their emphasis was rather on the use of unlawful means to achieve such purpose. 29. Thus, in R v Graham and Burns,[30] many persons assembled with the common purpose of holding a public meeting in Trafalgar Square to demand the release of certain Irish politicians, but the emphasis in Charles J’s direction to the jury (which has often been cited) was on the unlawfulness of the means adopted to pursue that objective: “It has not been suggested that the object of that meeting was not perfectly innocent. There is no doubt whatever that a meeting of British citizens can be held to protest, if they think fit, against the imprisonment of Mr O’Brien, but that is not the point… [The] question is, whether the mode in which it was attempted to assert the right of meeting in Trafalgar-square was or was not unlawful, that is the question you have to consider and decide.”[31] 30. In Field and Others v The Receiver of Metropolitan Police,[32] a number of youths conducted themselves in a disorderly way, pushing against a wall, leading to its collapse. As soon as it fell the caretaker of the premises came out into the street and the youths then dispersed in different directions. Phillimore and Bray JJ conducted a review of the early English authorities, including Lord Coke, Blackstone, Hawkins, Stephen and Lord Holt CJ which revealed markedly different views. Their Lordships concluded from the passages cited: “... that there are five necessary elements of a riot—(1.) number of persons, three at least; (2.) common purpose; (3.) execution or inception of the common purpose; (4.) an intent to help one another by force if necessary against any person who may oppose them in the execution of their common purpose; (5.) force or violence not merely used in demolishing, but displayed in such a manner as to alarm at least one person of reasonable firmness and courage.”[33] 31. Their Lordships therefore held that a riot required proof of a common purpose and its execution “or inception” (elements (2) and (3)). While they considered that there was evidence to justify the judge’s finding that those elements were satisfied, they commented that they “should not have found the same way.” However, the appeal was allowed on the basis that elements (4) and (5) had not been established. The youths had run away when the caretaker emerged so that there was no evidence of any “intent to help one another by force if necessary against any person who may oppose them in the execution of their common purpose”. [34] 32. In R v Caird,[35] the Cambridge riot might be said to have involved the extraneous common purpose of wrecking the restaurant and Greek-themed dinner for political motives. However, Sachs LJ stressed that what mattered was the violence of the protesters’ conduct: “When there is wanton and vicious violence of gross degree the Court is not concerned with whether it originates from gang rivalry or from political motives. It is the degree of mob violence that matters and the extent to which the public peace is being broken.”[36] 33. In R v John McKinsie Jones,[37] a case where picketers who were trying to force a work stoppage visited several different sites sequentially, James LJ stated: “The ingredients of the offence are (i) the actus reus of being or coming together—the assembly, and (ii) the mens rea involved in the intention of fulfilling a common purpose in such a manner as to endanger the public peace.” So again, while a common purpose was mentioned, it was the manner in which it was pursued, endangering the public peace, that was important. 34. McHugh JA (as His Honour then was) when sitting in the New South Wales Court of Appeal,[38] examined the English authorities and stated: “Despite the antiquity of the offence, the precise elements of the offence of riot are not settled. But there is almost unanimous agreement that an essential element is that the rioters must have an intention mutually to assist one another against any person who opposes them.”[39] 35. The mutual assistance element is derived from Hawkins, Pleas of the Crown (1st ed, 1716), Bk 1, p 155. The judgment holds that it was essential for the assembled persons to have a common purpose and an intention to render such mutual assistance: “... the authorities strongly support the proposition that it is an essential element in the offence of riot that each of the participants had the intention to help each other, by force if necessary, against any person who might oppose them in the execution of their common purpose. It necessarily follows that, if a number of persons are charged with the one offence of riot, they must have each had both a common purpose and an intention to help each other, by force if necessary, against any person who might oppose them in execution of that common purpose.”[40] 36. When the English Law Commission reported on Offences Relating to Public Order,[41] it stated, “There is no agreement as to precisely what constitutes an unlawful assembly” and counselled against relying on the authority of the older institutional writers. In relation to “common purpose”, they adopted the alternatives forming part of a working definition of the offence put forward by Smith & Hogan,[42] namely: “(1) An assembly of three or more persons; (2) a common purpose (a) to commit a crime of violence or (b) to achieve some other object, whether lawful or not, in such a way as to cause reasonable men to apprehend a breach of the peace.” 37. Subsequently, the common law offences of unlawful assembly and riot (as well as rout and affray) were abolished and replaced by new statutory offences under the Public Order Act 1986 in England and Wales. Notably, the offence of riot as defined by section 1 is differently structured from the offence under POO section 19 and expressly requires proof of a “common purpose” to be inferred from conduct.[43] B.2 “Common purpose” and sections 18 and 19 38. In our jurisdiction, statutory changes were introduced somewhat earlier by the Public Order Bill 1967 (“POB”).[44] At the Bill’s First Reading, the Attorney-General[45] explained that it was a codifying Bill, stating that it was: “... intended to be a comprehensive piece of legislation dealing with all aspects of public order ... [and] more than a mere consolidation of existing laws ... the opportunity [having] been taken to expand certain provisions and to fill in some gaps ...” He added: “Some of the requirements of the common law in relation to these offences were rather technical and ill-adapted to modern conditions. Although the basic principles of unlawful assembly and riot have been retained therefore certain modifications have been made.” 39. The Objects and Reasons of the Bill[46] make it clear that sections 18 and 19 “replace the common law” as part of the codification exercise. In particular, the intention is to eliminate any requirement for proof of a “common purpose”: “Clauses 18 and 19 introduce provisions dealing with unlawful assemblies and riots and replace the common law in this respect. The proposed statutory provisions are not identical with the common law, which is not adequate in certain respects for local circumstances. Firstly, there will no longer be the necessary element of common purpose before a crowd is an unlawful assembly or a riot. Secondly, an unlawful assembly will become a riot if any person taking part in the assembly commits a breach of the peace.” (Italics supplied) 40. The drafters of the POO were evidently aware of the uncertainties concerning the element of “common purpose” at common law. As we have seen, a common purpose – in the sense of an extraneous common purpose – is not one of the elements of either offence as presently enacted. The Objects and Reasons indicate that this was a deliberate feature of the codification. Thus, it is preferable not to refer to “common purpose” but to recognise instead the requirement of a participatory intent, reflecting the participatory nature of the two offences. It is in any event clear that no requirement for proof of an extraneous common purpose exists. 41. As previously noted, that was the approach to section 18 adopted by Lam JA (as Lam PJ then was) in SJ v Leung Kwok Wah.[47] His Lordship held that the elements of the offence reflected what he called the “corporate” nature of the offence: “... the conduct of the defendants had to be assessed together to see whether this criterion can be satisfied. There must be a sufficient nexus between the conduct of these defendants to justify having them considered together. And the fear required is that such persons so assembled, viz acting together, will commit a breach of the peace.”[48] 42. He added: “... if three persons in a lawful assembly committed acts of the prescribed nature at different parts of the place of assembly for different purposes, sparking off different incidents, involving and affecting an entirely different mix of persons, there would not be a sufficient nexus to turn these independent acts into an unlawful assembly of those three persons.”[49] 43. His Lordship was thus concerned with identifying the participatory requirements of unlawful assembly as a matter of statutory construction and held that the “corporate nature” of the offence entailed proof of a “common purpose” in the sense of what we have called a “participatory intent”. This is how his statement that “the requirement of having a common purpose in acting in the statutorily prescribed manner remains good law in dealing with a charge under s 18”[50] should be understood. He was certainly not suggesting that an additional element involving proof of an extraneous common purpose is required. 44. A Pang J below adopted the same approach, stating in her written directions that a necessary ingredient was that the relevant defendant “assembled together with those people for the common purpose of conducting themselves in a disorderly, intimidating, insulting or provocative manner”.[51] She was thus referring to an intention to take part in the unlawful assembly by doing the prohibited acts, not to an extraneous common purpose. 45. The Court of Appeal endorsed Lam JA’s approach[52] stating (in translation): “According to the true construction of s 18(1), the actus reus that constitutes unlawful assembly must have corporate nature to satisfy the requirement of offenders being jointly responsible. The offenders must have assembled together and conducted themselves in the manner prescribed in the ordinance when assembling. The offenders must have a common purpose so that the court can regard them as assembling to act together. Therefore, the requirement of having a common purpose is still applicable to s 18(1). In other words, the common law requirement of having a common purpose remains an ingredient of the offence of unlawful assembly under s 18(1).”[53] 46. The “common law requirement of having a common purpose” is clearly a reference to a participatory intent. The Court made this clear by adding: “... if the offenders just had the common purpose of conducting themselves in the prescribed manner, it is sufficient to satisfy the requirement of common purpose under s 18(1)”.[54] The Court was not endorsing an “extraneous common purpose”. Indeed, the submission that such a purpose is required was rejected as “completely wrong in law”.[55] 47. The foregoing analysis is equally applicable to the offence of riot. A defendant committing the offence must have a participatory intent. He or she must intend to take part in the riot along with other participants in the riotous assembly. No extraneous common purpose has to be shown. 48. The notion of an extraneous common purpose poses conceptual and practical problems. Rioters may nurture various purposes: to attack the police; to breach a police cordon so as to attack a target on the other side; to disrupt a transportation or other infrastructural system; to oppose a government policy; to cause a government minister to resign; and so forth. They might even be motivated to riot in return for payment by an instigator. Quite apart from the practical difficulties of proving that one or other purpose was shared by the defendants, arguments would arise as to how the extraneous common purpose should be formulated and as to whether motive has to be distinguished from purpose in this context. In contrast, proof of a defendant’s participatory intent may generally be inferred from his or her conduct. 49. Ms Li SC submitted that it is necessary to prove that a defendant took part in a particular unlawful or riotous assembly, sharing a specific extraneous common purpose with other participants in that peculiar assembly, such purpose and such assembly to be identified and spelt out in the indictment and distinguished from other unlawful or riotous assemblies pursuing different extraneous common purposes, forming part of the general mob. Those submissions are rejected. We have already excluded any requirement of proving an extraneous common purpose. Certainly nothing in the language or intent of sections 18 and 19 lends any support for the unworkable and unrealistic approach espoused by Counsel. 50. We would therefore answer Questions 1a and 1b in Annex 1, which postulate the possible requirement of an extraneous common purpose, in the negative. As to Question 1c, as explained above, the defendant must have a participatory intent, intending to participate in the unlawful assembly or riot in concert with other participants, being aware of their related prohibited conduct. We would answer Question 1d, which addresses what we have called a “mutual assistance” element, in the negative as it represents an aspect of the common law that is no longer applicable. C. Joint enterprise and sections 18 and 19 51. Question 2a in Annex 1 asks “Whether the doctrine of joint enterprise applies to the offences under sections 18 and 19 of the POO”. Question 1 in Annex 2 is to like effect. In answering those questions, it is important to note, as explained in HKSAR v Chan Kam Shing,[56] that the common law has developed two forms of the joint enterprise doctrine, referred to as the basic and extended forms. C.1 Basic Joint Enterprise (“BJE”) and Extended Joint Enterprise (“EJE”) 52. The basic form (which Lord Hoffmann called “the plain vanilla version of joint enterprise”[57]) – BJE – involves the co-adventurers simply agreeing to carry out and then executing a planned crime. It is taking part in this criminal joint enterprise that makes all participants guilty as principals, whoever the actual perpetrator(s) of the actus reus might have been. Such liability is independently based on each defendant’s participation in the joint criminal enterprise with the requisite mental state to constitute the offence relevant to the defendant in question.[58] The doctrine is especially efficacious in dealing with situations of evidential uncertainty where, for instance, it is clear that A and B agreed to carry out a murder but it is unclear whether A or B actually struck the fatal blow. Of course, if it is known that both A and B struck the blows which cumulatively killed the victim, they would be jointly guilty of murder as principals. And if it was known that A did the killing while B was present and helped or encouraged A to do it, B would be guilty on the basis of secondary liability as an aider and abettor.[59] And if the agreement to commit the murder is proved, both are liable as conspirators. 53. The extended version of joint enterprise – EJE – addresses the situation where certain defendants (say A, B and C) agree on a certain BJE but, where in the course of carrying out the agreed plan (say, a burglary), one of them (say A) commits a more serious offence (say, murder). The common law (as applied in Hong Kong)[60] holds that B and C are equally guilty of A’s crime on the basis of EJE if it is proved that A’s commission of the further offence (if murder, meaning his acting with intent to kill or at least to cause grievous bodily harm) was foreseen by them as a possible incident of the execution of their planned joint enterprise. 54. As was pointed out in Chan Kam Shing,[61] the joint enterprise doctrine operates alongside the traditional accessorial liability principles. Thus, CPO section 89 makes any person who aids, abets, counsels or procures the commission by another person of any offence guilty of the like offence and so punishable to a like extent. The joint enterprise doctrine also operates alongside the principles relating to inchoate liability for conspiracy, incitement and attempt which are also punishable to the like extent as the principal offences.[62] 55. In examining how far the joint enterprise doctrine applies to unlawful assembly and riot, two questions arise in the present context: (i) is the doctrine invoked in the courts below the BJE or the EJE form of the doctrine? (ii) What consequences does the prosecution allege to flow from application of the doctrine to unlawful assembly and riot? C.2 The Judge’s summing-up and the Court of Appeal’s decision in the Lo Case 56. The trial Judge summed up for the jury on the footing that the defendants could be convicted on the basis of joint enterprise and elaborated as follows (in translation): “If two or more people commit criminal offences together, as mentioned before, but I read out once again, even if each person assumes a different role, if they act in accordance with a common criminal enterprise or agreement, each shall be guilty. Similarly, the words ‘plan’ and ‘agreement’ do not mean that there has to be any formality about it. An agreement commit an offence may arise on the spur of the moment. Nothing needs be said at all. It can be made with a nod and a wink, or a knowing look, or it can be inferred from the behaviour of the parties. The essence of the joint culpability for a criminal offence is that each defendant shares a common intention to commit the offence and played his part in it (however great or small) so as to achieve that common object. In other words, the prosecution alleged in his case that with regard to Counts 3 and 4, they said that the defendant in question committed the offence of riot together with the other defendants listed in the charges.” 57. And in relation to riot, in her written directions, her Ladyship stated: “Where a criminal offence is committed by two or more persons, even if each of them may play a different part, but where they are acting together as part of a joint plan or agreement to commit the offence, each one of them is guilty.”[63] 58. The Judge’s direction therefore concerned a BJE involving participation in an unlawful or riotous assembly. 59. In the Court of Appeal, the focus was on an alleged misdirection on “common purpose”[64] and the Court did not comment on the applicability of the doctrine of joint enterprise while upholding the conviction. It therefore implicitly accepted that the BJE doctrine applies to sections 18 and 19. C.3 The decisions of the Judge and the Court of Appeal in the Tong Case 60. The issue was directly addressed both at first instance and in the Court of Appeal in the Tong Case. The Judge had acquitted the defendants, declining to find by inference that they had been physically present and either taking part in the riot in person or encouraging others who were committing the offence. His Honour also rejected the prosecution’s contention that even if the defendants were not present as part of the said assembly, they should be convicted as participants in a joint enterprise with other rioters. He held that the doctrine was excluded as a matter of statutory construction.[65] As we have seen, this caused the Secretary for Justice to submit questions for the opinion of the Court of Appeal now reproduced in Annex 2 of this judgment. The objective of the Secretary for Justice was to establish that, by operation of the joint enterprise doctrine, it is possible to fix a defendant with liability for riot as principal without that person being present at the scene of the riot. 61. Poon CJHC, with whom the other members of the Court of Appeal agreed, held that Questions 1 and 2 should be answered in the affirmative, taking the view that the joint enterprise doctrine filled what would otherwise be a significant gap in the law of unlawful assembly and riot. He was particularly anxious to hold that persons who played important roles in unlawful assemblies and riots while not physically present at the scene of the criminal assembly should not escape liability: “... unlawful assemblies and riots nowadays are highly fluid in nature. They involve a myriad of participants playing various roles and sometimes with a rather sophisticated division of labour among them. Some physically participate in the unlawful assembly or riot at the scene. Some aid or abet the participants at the scene. Some may not even be present but are clearly participants under the doctrine of joint enterprise. Take the following examples: (1) A mastermind of the unlawful assembly or riot who remotely oversees the situation and gives commands or directions to the participants on the ground. (2) A person who funds or provides materials for the unlawful assembly or riot. (3) A person who encourages or promotes the unlawful assembly or riot by making telephone calls or spreading messages on social media. (4) A person who provides back-up support to the participants in the vicinity of the scene, such as collecting gear, bricks, petrol bombs, other weapons, and other materials to be used by the participants. (5) A lookout stationed in the vicinity who alerts the participants to the advance or deployment of the police. (6) A person who drives a getaway car to allow the participants to leave the scene.”[66] 62. It is evident that Poon CJHC was, like the trial Judge in the Lo Case, referring to the BJE form of the doctrine. The only offences under consideration were the offences of unlawful assembly or riot. No one was seeking to charge any of the participants with a more serious offence committed in the course of their agreed criminal venture so that no question of EJE arose. C.4 On the applicability of the joint enterprise doctrine 63. In our view: (a) On a proper construction of sections 18 and 19 of the POO, the joint enterprise doctrine is not applicable as a basis for fixing a defendant with liability for the offences of riot or unlawful assembly as a principal if he or she was not present at the scene and was not taking part in the criminal assembly. (“The absence point”) (b) On their true construction, POO sections 18 and 19 leave no room for operation of the common law doctrine in its BJE form because the statutory language renders that doctrine otiose and its application would give rise to duplication and possible confusion regarding the central actus reus element of “taking part” in the criminal assembly. (“The taking part point”) (c) The EJE form of the doctrine may be applicable if certain participants in the unlawful assembly or riot can be proved to have foreseen commission by one or more of their number of a more serious offence as a possible incident of the execution of their planned joint participation in the unlawful assembly or riot. (“The EJE point”) (d) The foregoing propositions do not affect potential secondary or inchoate liability for offences under sections 18 or 19 of persons who are not present at the scene. C.5 The absence point 64. The issue here is whether a defendant who is absent and so does not take part in the unlawful or riotous assembly together with others so assembled, can be found guilty of unlawful assembly or riot as a principal offender on the basis of the BJE doctrine. As noted previously, the Court of Appeal in both the Lo Case[67] and the Tong Case[68] omitted reference to the centrally important actus reus element of “taking part” in sections 18 and 19. That resulted in focus on the participatory nature of the offences being lost. 65. As analysed in Sections A.1 to A.3 of this judgment, guilt as a principal offender requires proof that the defendant engaged collectively with other participants in or in furtherance of the prohibited conduct or breaches of the peace. The Ordinance defines participatory offences requiring a defendant not just to “take part”, but to do so as part of an “assembly”, as a person “assembled together” with others taking part. Thus, its language imports a requirement of presence at the scene before one can be held guilty as a principal offender. Such a statutory requirement cannot be displaced by the common law BJE doctrine. The proposition that at common law, a defendant may in certain circumstances be held guilty as a principal according to his own mens rea even though he was not present at the scene where the actus reus was committed only holds good where operation of that doctrine is not excluded by inconsistent statutory provisions. In Chan Kam Shing[69] and Sze Kwan Lung[70] the doctrine was applicable since the substantive offences involved were murder and manslaughter and not statutory offences requiring presence at the scene. C.6 The taking part point 66. This point, which concerns the applicability of the joint enterprise doctrine where the defendant is present at the scene, also flows from recognising the centrality of “taking part” as the actus reus of both offences. Since, as we have just seen, the offences under sections 18 and 19 require proof of the defendant taking part in the disorderly or riotous conduct in common with the other persons assembled, it is otiose and confusing to introduce as a requirement, a prior layer of common intention and collective conduct which merely mirrors the statutory requirement of “taking part”. 67. As noted above, a BJE involves the co-adventurers agreeing to carry out and then executing a planned crime. With the offences of unlawful assembly and riot, proving that the defendants executed their plan would provide proof of their “taking part” in the unlawful assembly or riot and thus establish guilt of the statutory offences, without any need to pray in aid the doctrine of joint enterprise. Their participatory intent would be inferred from their prohibited conduct while assembled together, so from the prosecution’s viewpoint, invoking the BJE doctrine would add the unwarranted burden of showing a prior agreement. From the trial Judge’s point of view, jettisoning BJE in this context would avoid possibly confusing the jury by trying to explain two layers of “taking part” – first in the joint enterprise and then in the unlawful or riotous assembly. 68. This analysis does not leave any gap. As was pointed out in Chan Kam Shing,[71] while a principal carries out the prohibited conduct with the necessary mens rea and an aider and abettor is one who is present and renders assistance or encouragement to the principal in the commission of the offence, liability as a counsellor or procurer does not require the defendant’s presence at the scene: “A person who counsels or procures an offence (referred to also as an accessory before the fact) is not present but provides assistance or encouragement prior to the commission of the offence. Such a person performs the actus reus of ‘procuring’ an offence ‘by setting out to see that it happens and taking the appropriate steps to produce that happening’. A person ‘counsels’ an offence by soliciting or encouraging its commission.”[72] Nor does a defendant who commits the inchoate offence of conspiracy or incitement have to be present at the scene where the principal offence is committed. 69. Thus, to take the examples given by Poon CJHC:[73] The “mastermind” who remotely oversees the situation and gives commands or directions to the participants on the ground would be guilty of incitement or as counsellor and procurer of the criminal assembly. So would the persons who fund or provide materials for the unlawful assembly or riot; or who encourage or promote it on social media. Those who provide back-up support to the participants in the vicinity of the scene, collecting bricks, petrol bombs and other weapons; or who act as lookouts in the vicinity of the riot may either be “taking part” as principals under the POO or liable as aiders and abettors if present at the scene; or, if not present, liable as counsellors or procurers. The culpability of the person who drives a getaway car to help participants leave the scene is likely to include liability for assisting an offender under section 90 of the CPO.[74] 70. There is accordingly no lacuna.[75] Public order can be fully enforced relying on secondary liability and inchoate offences, consistently with the true construction of the statutory offences and without stretching the concept of being “assembled together” beyond its proper limits. As previously pointed out, persons so convicted as accessories or for inchoate crimes are punishable to a like extent as principal offenders.[76] C.7 The EJE point 71. The difficulties associated with applying the BJE doctrine to unlawful assembly or riot do not arise in relation to EJE. There is no duplication or confusion since the liability based on the EJE doctrine relates to the further offence committed in execution of the plan and not just to taking part in the criminal assembly in question. 72. To take a hypothetical example, A, B and C may be among numerous other persons taking part in a riot (satisfying all the statutory elements of the offence) and C then proceeds to commit a further offence – say, of murder, by deliberately stabbing someone to death. If A and B are shown to have participated with C in the riot and foreseen that C might commit murder, meaning his assaulting a victim with intent to kill or with intent to cause grievous bodily harm as a possible incident of the execution of their planned participation in the riot, they could be found guilty of murder on the EJE basis. 73. The point does not arise in the present case since no EJE case is sought to be made against Lo. It is however not an unrealistic consideration. It might, for instance, be possible to prove that a group of persons agreed to take part together in a riot, intending to destroy public property and to erect barriers stopping traffic, while knowing that some amongst them would take along petrol bombs or potentially lethal weapons which they might use. If they proceeded with their plan and the petrol bombs or other weapons were then used to cause serious injury, the EJE doctrine might apply to fix the rioters who foresaw the intentional infliction of such injury as a possible incident of the execution of their agreed plan with liability for the more serious offence. C.8 Presence and the location and scope of the assembly 74. The Court noted in Kwok Wing Hang v Chief Executive in Council,[77] that at the height of the disturbances in 2019: “The frequency of outbreaks of violent protests increased and the locations at which they took place also spread from one or two areas to become a phenomenon described colloquially as ‘blossoming everywhere’in which multiple outbreaks of violence happened simultaneously on Hong Kong Island, in Kowloon and in the New Territories.” 75. And as Poon CJHC observed in the Tong Case:[78] “... unlawful assemblies and riots nowadays are highly fluid in nature.” He pointed to participants assuming different roles and communicating with each other using their phones and on social media. Offenders could not be expected to be assembled as a stationary group with a fixed membership in a single location. Participants would move around in varying groups along main thoroughfares, running into side streets and buildings, spreading out and re-coalescing whether in response to action by the police, in pursuit of different targets or for other reasons. Violence would periodically flare up and die down. Participants would often be in communication with each other, coordinating their activities. 76. It will be necessary in each case for the tribunal to determine where and when an unlawful assembly or riot took place and whether a defendant, if charged as a principal, was present and took part. However, the abovementioned fluidity should be taken into account and an overly rigid view should not be taken of what constitutes the assembly, its location and duration. Evidence regarding the geographical area affected, the conduct of and communications maintained among the participants and the duration of the disturbances should be considered as a whole. The defendant’s role in the assembly, if any, should be considered for the purposes of assessing his or her potential principal, accessorial or inchoate liability. 77. A realistic view should be taken of the duration of the unlawful assembly or riot. So long as three or more participants remain actively engaged in the criminal assembly (not necessarily including the constituent offenders establishing the unlawful assembly nor the person or persons whose breach or breaches of the peace transformed the unlawful assembly into a riot – they may have left), the unlawful assembly or riot remains in being as a matter of law. Such an assembly remains in being as long as the participants remain at the scene even if, in the case of a riot, the violence ebbs and flows. Any person taking part in such a riotous assembly commits the offence. 78. The focus should be on whether the evidence directly proves or supports an irresistible inference that the defendant had taken part in the unlawful assembly or riot. Evidence which might support such an inference could include such matters as the time and place of arrest and items found on the defendant, such as a helmet, body armour, goggles, a respirator, a radio transceiver, plastic ties, laser pointers, weapons and materials to make weapons such as petrol bombs which might have been used by those taking part in the criminal assembly. Such fluidity and the basis of the defendant’s alleged liability should also be borne in mind in the drafting of the charge, catering for alternative possibilities. D. Encouragement 79. Question 2d in Annex 1 asks whether a person can be found guilty of riot “without specific conduct on his part falling under the prescribed conduct provided in sections 18 and 19”, but “merely by virtue of alleged encouragement through his presence”. 80. In her directions to the jury, the Judge stated (in translation): “... mere presence at the scene of crime is not enough to prove guilt. But if you are sure that a particular defendant was at the scene, deliberately by his [mere] presence tried to and did encourage the others to use violent [sic] or threaten to use violence; or if you are sure that his presence at the scene was for playing his role in achieving the purpose of committing riot as jointly agreed by him and other defendants, then he (that is, the defendant) is guilty.” The second occurrence of the word “mere” does not represent a correct translation of the original Chinese and is ignored. 81. It is obviously important to avoid treating innocent passers-by who find themselves caught up in an unlawful assembly or riot as guilty of an offence just because they were present at the scene. Presence at the scene in itself is not enough to constitute “taking part” or aiding and abetting.[79] As the Queensland Court of Appeal held in R v Cook,[80] at common law, mere presence in an unlawful assembly or riot is generally insufficient to found liability. It has traditionally been considered necessary that there be some intentional activity in furtherance of the riot.[81] 82. That is not to say that the bar is set high. It does not take a great deal of activity on the defendant’s part to move the case from the “mere presence” to the “encouragement” category. Thus, in 1810, Mansfield CJ stated in Clifford v Brandon:[82] “The law is, that if any person encourages or promotes, or takes part in riots, whether by words, signs, or gestures, or by wearing the badge or ensign of the rioters, he is himself to be considered a rioter, and he is liable to be arrested for a breach of the peace.” 83. This was echoed more recently in Caird,[83]where Sachs LJ said: “It is the law … that any person who actively encourages or promotes an unlawful assembly or riot, whether by words, by signs or by actions, or who participates in it, is guilty of an offence which derives its great gravity from the simple fact that the persons concerned were acting in numbers and using those numbers to achieve their purpose.” 84. And as Byrne J stated in R v Cook:[84] “Generally, mere presence at the scene of a crime does not involve criminal responsibility. But presence to facilitate the commission of an offence by others has every potential to attract criminal responsibility under s 7 [of the Criminal Code (Qld)]. And so those present to ‘lend the courage of their presence to the rioters, or to assist, if necessary’ may be guilty with the active participants.” 85. Whether a defendant has done enough to constitute “taking part”, especially if by way of encouragement, is a matter of fact and degree, taking all the circumstances into account. 86. Question 2d contains certain rolled-up propositions. Aiders and abettors or counsellors and procurers may obviously perform acts which are not themselves acts of disorderly conduct or breaches of the peace but which offer encouragement or assistance to others in the commission of such acts, thus founding secondary liability (or, as previously explained, possibly also liability as principals for “taking part”). Thus, if the defendant’s presence occurs in circumstances qualifying it as “encouragement” of the prohibited conduct by others, then the answer to Question 2d would be in the affirmative. But mere presence without more is not treated as encouragement, whether for the purpose of “taking part”, or accessorial or inchoate liability. 87. In her summing-up (including in her written directions), the Judge did on a number of occasions correctly direct the jury that their task was to decide whether the appellant had taken part in the riot, coupled with the requirement of a “common purpose” in the sense of a participatory intent discussed above. The case against Lo was that he was a principal offender who had repeatedly performed acts amounting to breaches of the peace. He was not just an innocent by-stander nor even someone who had merely encouraged others. The appellant’s defence was that he had been misidentified, a defence which the jury plainly rejected. E. Breach of the peace 88. As we have seen, breaches of the peace are the distinguishing feature of a riot. In this jurisdiction, R v Howell[85] has often been cited as authority for what constitutes such a breach. Watkins LJ there stated: “... there is a breach of the peace whenever harm is actually done or is likely to be done to a person or in his presence to his property or a person is in fear of being so harmed through an assault, an affray, a riot, unlawful assembly or other disturbance. It is for this breach of the peace when done in his presence or the reasonable apprehension of it taking place that a constable, or anyone else, may arrest an offender without warrant.”[86] 89. With its focus on an act which actually harms a person, or in his presence, harms his property, or is likely to cause such harm, etc, this appears to be a markedly narrow formulation. In recent experience, rioters have often engaged in wanton damage to property which is not privately owned and not done in the presence of the owner – such as tearing down road railings to make barriers, digging up bricks to use as projectiles, smashing traffic lights, damaging CCTV cameras, throwing Molotov cocktails into Mass Transit Railway stations and vandalising shops identified with persons of opposing political views. Such acts often occurred in the middle of the night when the premises were closed and no owner was present. Plainly, such conduct also constitutes breaches of the peace. 90. In R (Laporte) v Chief Constable of Gloucestershire,[87]Lord Bingham of Cornhill put the proposition derived from Howell more widely, stating that “the essence of the concept was to be found in violence or threatened violence”. We would adopt that as a general approach to the phrase “breach of the peace” in the context of section 19. Someone who commits or threatens an act of violence against another person or another’s property or acts so that such violence may reasonably be apprehended, commits a breach of the peace. 91. As is apparent from the passage cited above, Watkins LJ’s statement in Howell was made in affirming the existence of a common law power of arrest without warrant. His reason for referring to the presence of the person apprehending a breach of the peace is indicated as follows (especially in the words italicised): “... even in these days when affrays, riotous behaviour and other disturbances happen all too frequently, we cannot accept that there can be a breach of the peace unless there has been an act done or threatened to be done which either actually harms a person, or in his presence his property, or is likely to cause such harm, or which puts someone in fear of such harm being done. There is nothing more likely to arouse resentment and anger in him, and a desire to take instant revenge, than attacks or threatened attacks upon a person’s body or property.”[88] 92. Thus, the power of arrest, based on an apprehended breach of the peace, was held to arise so that such situations could be prevented from deteriorating into public disorder involving provoked retaliation by persons present and feeling threatened in respect of their persons or property. 93. In POO sections 18 and 19, that policy consideration is covered by element [4]. Conduct prohibited under section 18(1) includes conduct which would “provoke other persons to commit a breach of the peace”. Thus, the concept of a “breach of the peace” in sections 18 and 19 includes, but is not confined to, situations which might give rise to provoked retaliation as envisaged in Howell. In cases involving actual or threatened violence to property, the owner of such property need not be present for there to be a breach of the peace. F. Substantial and grave injustice: non-conviction of the named co-defendants 94. The indictment against Lo alleged that: "LEUNG Tin-kei, LEE Nok-man, LO Kin-man [the appellant] and LAM Ngo-hin, between the 8th day of February, 2016 and the 9th day of February, 2016, at Portland Street, Mong Kok, Kowloon, in Hong Kong, took part in a riot.” 95. Where justified by the evidence, it is common (and good practice) to add the allegation that the defendant’s participation in the unlawful assembly or riot was also “with persons unknown” or “with persons not before the court”. That was not done in Lo’s case and, at the end of the trial, while he was convicted, the jury were unable to reach a verdict in respect of the other three named defendants. Since the offence requires proof of the collective action of at least three persons assembled together as a constituent element, it was a material irregularity to convict the appellant alone without an averment in the indictment regarding the existence of other constituent offenders. Lo argues that this amounted to such a substantial and grave injustice as to require the quashing of his conviction. 96. Such a situation was addressed by the English Court of Appeal in R v Abdul Mahroof,[89] where the appellant was charged with two others (named Biney and Sayers) with violent disorder contrary to section 2 of the Public Order Act 1986, an offence which is constituted “Where three or more persons who are present together use or threaten unlawful violence and the conduct of them (taken together) is such as would cause a person of reasonable firmness present at the scene to fear for his personal safety ...”. 97. The facts were decidedly different from the present case. The evidence was that the appellant and Sayers went to Biney’s home to confront him about a debt he owed the appellant. The threatened violence was alleged only to involve those three men, they being the only persons named in the indictment as participants. A witness testified that there were also two other persons present but they “appeared to be on the fringe of the argument by just adding the odd word during the argument”.[90] The jury acquitted Biney and Sayers, and the question arose whether, given the elements of the offence, the appellant could nonetheless be convicted on his own. 98. On this issue, the Lord Chief Justice stated: “... the question comes down to this: Was it a sufficient allegation in the indictment if no mention was made in the indictment of any other potential participant except the three men, namely, Biney, Mahroof and Sayers? ... It seems to us that the answer to that, and as a consequence the answer to the certified question, is ‘Yes, subject to two very important qualifications’: first of all, that there is evidence before the jury that there were three people involved in the criminal behaviour, though not necessarily those named in the indictment; secondly, that the defence are apprised of what it is they have to meet.”[91] 99. The Court held that it was a material irregularity to convict the appellant in the circumstances. Application of the proviso was considered but, on the facts described above, the Court felt unable to say that there was no miscarriage of justice. The only other persons who might have supplied the needed three participants were the two men at the fringes of the argument, offering little basis on the evidence for being treated as constituent offenders under section 2. The Court decided instead to substitute a conviction for an offence that did not depend on the participation of others. 100. The circumstances of Lo’s case are very different. It is important to note that the guilt of a defendant charged under POO sections 18 or 19 is not dependent on the conviction of anyone else. The prosecution must prove that he or she took part in the criminal assembly which was constituted by at least three persons. If the evidence is incontrovertible that there was such a criminal assembly and that the defendant took part in it with the necessary participatory intent, the elements of the offence are proved and the fact that no one else was charged or convicted, including the only persons named as co-participants, does not exonerate the defendant. In cases where the defendant is convicted but not the only other alleged participants, the failure to include a reference in the indictment to “persons unknown” or “persons not before the court” as co-participants is a material irregularity but by no means necessarily fatal to the prosecution. 101. There was undoubtedly evidence before the jury in the present case that there were at least three persons other than his co-defendants who had taken part in the criminal assembly in which Lo had participated. Thus, the Court of Appeal noted that some 500 people gathered on Portland Street that night behaving in a riotous manner[92] and considered it incontrovertible that Lo (referred to as the 2nd applicant) directly took part in the riot: “The 2nd applicant appeared in Portland Street back at around 9 o’clock in that evening, assisting the hawkers to push hawker trolleys out to the pavement; and subsequently he together with others scolded the FEHD staff and obstructed the police in the investigation of the taxi incident. Police officers testified that they witnessed the 2nd applicant twice throwing objects from the crowd to the police line. The footage produced in court also showed that the 2nd applicant at later stages threw objects to the police line and picked up mud and sand from the ground to attack the police for a total of 11 times.”[93] 102. The evidence of the mob’s activity was described in detail, the Court of Appeal observing[94] that: “The trial judge took into consideration that there were some 500 people gathering on Portland Street, and that the crowd confronted the police for almost four hours, threw objects at the police line, splashed liquid in front of the police line and put up resistance by holding weapons, and also that a police officer was persistently kicked on his head after being pushed to the ground. Moreover, the case happened in a very crowded area of the city on the night of Lunar New Year Day. The violence involved caused extreme danger to the safety of citizens. In the course of it, someone was hit by a concrete slab thrown out, immediately fell onto the ground and lost consciousness. Someone was injured and bled as a result of being struck by a brick. The trial judge found the violence on Portland Street to be of large scale and extremely serious.” 103. The trial Judge’s written directions required the jury to be sure that Lo did take part in an unlawful assembly and a riot involving “3 or more than 3 persons assembled together”, not limited to his named co-defendants. Her Ladyship expanded on this in her oral directions: “The third point is in relation to Count 3 we reviewed yesterday, namely the riot on Portland Street where [Lo] was involved. You will remember what I said. I said that the prosecution relied on the scene, the situation at the scene, the number and state of the crowd and the behaviour of [Lo] etc. to prove the first element of the offence of unlawful assembly ... Of course, the prosecution case, as I said, was to look at the overall situation on Portland Street, the number of people, and the actions of [Lo], etc. that night. He asked us to infer that at Portland Street that night [Lo] did take part in an unlawful assembly.” 104. It was on this basis that the Court of Appeal noted that in sentencing Lo, “the trial Judge held that he “had been actively taking part in the riot of Charge 3”.[95] There was thus ample evidence for the jury to be satisfied of Lo’s participation and so for the first condition referred to in R v Abdul Mahroof to be met. 105. There can also be no doubt that Lo was fully aware that the case against him was of his participation in the riot in Portland Street over some six hours, culminating in his arrest at about 3:00 am. He knew that the prosecution case, based on video footage, was that he had, among other things, on eleven occasions in the course of the riot, thrown objects at the police. He denied having done this, his defence being one of misidentification. But the jury obviously found the case against him proved beyond reasonable doubt. 106. Ms Li SC relied on R v Worton,[96] a case involving a fight in a public house, where the English Court of Appeal held that the two Mahroof conditions had been satisfied but, Lloyd LJ, giving judgment for the Court, went on to say: “In cases of this kind, where there are only three defendants accused of violent disorder, it is not in our view sufficient that the offence should be defined in general terms, as it was here. It is necessary that the Judge should go on and warn the jury specifically that if any one of the three defendants should be acquitted of violent disorder, then they must necessarily acquit the other two, unless satisfied that some other person not charged was taking part in the violent disorder. This the recorder in the present case never did.”[97] 107. While holding that a direction in the aforesaid terms is necessary, it is clear that Lloyd LJ was not ruling out application of the proviso in cases where that direction is not given. Thus he noted that the prosecution had invited the Court to apply the proviso but declined that invitation on the basis that “... we cannot be convinced that the jury would necessarily have reached the same result if they had been given a full and proper direction.”[98] 108. In the present case, in the light of the evidence described above, we are satisfied that the jury plainly would have reached the same conclusion if fully directed so that application of the proviso is appropriate. The case for quashing the conviction on the basis of substantial and grave injustice is not made out. G. Conclusions and disposition of the appeals 109. We summarise our conclusions as follows: (a) POO section 18 defines the elements which constitute an unlawful assembly and makes “taking part” in the unlawful assembly so constituted the actus reus of the offence. The constituent elements are for three or more persons assembled together to conduct themselves in the prohibited disorderly, etc, manner intended or likely to cause a reasonable apprehension that the persons so assembled will commit or provoke a breach of the peace. Any person who takes part in an unlawful assembly commits the offence. (b) POO section 19 builds on section 18, making the existence of an unlawful assembly one of the constituent elements of the offence of riot. A riot comes into being when any person taking part in an unlawful assembly commits a breach of the peace, turning the assembly into a riotous assembly. The offence is committed by any person who takes part in a riot so constituted. (c) Both offences are participatory in nature. The defendant must be shown not just to have been acting alone but to have taken part in the unlawful or riotous assembly, acting together with others so assembled, being aware of their related conduct and with the intention of so taking part, ie, with a participatory intent. There is no requirement for the persons taking part to share some extraneous common purpose. (d) To “take part” in the relevant criminal assembly, the accused must perform the acts prohibited, ie, by behaving in the prohibited disorderly, etc fashion (section 18); or committing a breach of the peace (section 19); or acting in furtherance of such prohibited conduct by facilitating, assisting or encouraging those taking part in the criminal assembly. (e) Mere presence at the scene of an unlawful or riotous assembly does not give rise to criminal liability. However, if the accused, being present, provides encouragement by words, signs or actions, he or she may be held to be “taking part” and guilty as a principal or held to be an aider and abettor. In deciding whether a defendant was present at the scene, the court should take into account the possible fluidity of the criminal assembly and the communications maintained by participants with each other in ascertaining the time, place and scope of the assembly in question. (f) To be guilty as principal offender under section 18 or 19, the defendant must be present at the scene, taking part in the unlawful or riotous assembly together with others so assembled. However, a person who promotes or acts in furtherance of an unlawful assembly or riot while not present at the scene may be guilty as a counsellor and procurer of the relevant offence or guilty of conspiracy or incitement to commit such offence and would be punishable to a like extent as the principal offender. Moreover, a person who assists an offender is liable under section 90 of the CPO. (g) The common law doctrine of joint enterprise in its basic form cannot operate in a manner inconsistent with the statutory language. It cannot be relied on to fix liability as a principal offender on a defendant who was not present and not acting as part of an assembly together with others so assembled, as required by the two sections. Even in cases where the defendant is present at the scene, the basic joint enterprise doctrine is inapplicable, being otiose and liable to cause confusion, since the actus reus of each of the statutory offences already involves “taking part” with others assembled together. (h) The inapplicability of the basic joint enterprise doctrine does not leave any gap since culpable conduct of absent defendants who engage in promoting or acting in furtherance of a criminal assembly is covered by secondary and inchoate liability offences. In given circumstances, the extended form of joint enterprise may operate to fix participants with liability for more serious offences committed in executing their joint plan. (i) “Breach of the peace” in the context of sections 18 and 19 includes, but is not confined to, situations which might give rise to provoked retaliation. It extends to cases involving actual or threatened violence to persons or property, without any need for the owner of such property to be present. (j) In drafting an indictment alleging unlawful assembly or riot against a defendant, it is good practice to allege, where the evidence permits, participation by other persons unknown. Failure to do so may be a material irregularity where the defendant is convicted but not the only other named defendants so that the requirement of 3 or more constituent offenders may not be met. In such cases, the question whether the proviso should be applied depends on whether the evidence plainly establishes that there were at least three persons involved in the criminal assembly in which the defendant took part and on whether the defendant fairly knew the case he or she had to meet. 110. Lo’s appeal must be dismissed. The ground of appeal[99] based on the submission that the Judge had erred in not requiring the jury to find an extraneous common purpose has been rejected.[100] The other grounds, reflected in the other questions in Annex 1 have little bearing on Lo’s case. While the trial Judge erroneously considered joint enterprise applicable, this had no practical effect in Lo’s case since his conviction does not depend on application of that doctrine. Nor was it alleged against him that he was guilty by having encouraged others by his presence.[101] The case against him, amply supported by the evidence and properly dealt with in the summing-up, was that he was present and actively took part in the riot over several hours. We have held that the content of the indictment and non-conviction of the other named defendants constituted a material irregularity but that this is a clear case for application of the proviso. 111. The Tong Case comes to this Court via a reference under CPO section 81D to the Court of Appeal on two questions of law. Since, by virtue of section 81D(4), such a reference does not affect Tong’s acquittal, the issues before this Court are confined to the questions of law set out in Annex 2. It is unnecessary and would be inappropriate to conduct a review of the trial Judge’s findings of fact. In answer to Question 1, we have held that BJE is inapplicable but that, in given circumstances, EJE may be applicable. As to Question 2, we have held that the doctrine attributing liability as a principal offender to a defendant who is absent by application of the BJE doctrine is inapplicable as inconsistent with the statutory language. We have emphasised that a defendant who promotes or acts in furtherance of an unlawful assembly or riot while not present at the scene may be liable as a secondary party or as a conspirator or inciter of the main offence and punishable to the same extent. We have also dealt with the effect of mere presence and what constitutes encouragement in the present context.[102] We have accordingly addressed the questions set out in Annex 2 and so disposed of Tong’s appeal. There is no need for any consequential orders to be made. FACC 6/2021 Ms Gladys Li SC and Mr Lawrence Lau (both assigned by the Director of Legal Aid), Mr Kin Lau and Mr Jason Ko (both on a pro bono basis), instructed by Bond Ng Solicitors, for the Appellant Mr Anthony Chau, DDPP(Ag), Mr Ivan Cheung, SPP, Ms Karen Ng, PP and Mr Wilson Lam, PP, of the Department of Justice, for the Respondent FACC 7/2021 Mr Philip Dykes SC, Mr Hectar Pun SC, Mr Anson Wong Yu Yat and Ms Ferrida Chan, instructed by S. T. Cheng & Co, for the Appellant Mr Anthony Chau, DDPP(Ag), Mr Ivan Cheung, SPP, Ms Karen Ng, PP and Mr Wilson Lam, PP, of the Department of Justice, for the Respondent Annex 1 Question 1a In order to establish the offence of riot under section 19 of the Public Order Ordinance (Cap 245) (“POO”), whether proof of the unlawful assembly required that at least 3 persons be assembled together for a “common purpose” which was distinct from the intention of committing the statutorily prescribed acts, namely, conducting oneself in a disorderly, intimidating, insulting or provocative manner; and therefore whether the Trial Judge had erred in law in directing the jury that the element of “common purpose” is satisfied if they are satisfied that the Applicant assembling together with other defendants had the intention of conducting themselves in a disorderly, intimidating, insulting or provocative manner? Question 1b If the answer to Question 1a is in the affirmative, whether there is a legal requirement that the said prescribed acts and the breach of the peace must be committed with the specific intent to achieve the “common purpose” by such means? Question 1c For the common purpose to be a substantive element in the offence of riot, whether the Prosecution is required legally to prove that such alleged common purpose must be shared, mutually understood or communicated between the accused to a standard that there is a meeting of minds, or the Prosecution is simply required to prove that the same purpose was held individually by the accused without the need to prove further mutual understanding or communication? Question 1d Whether it is a distinct element of riot under section 19 of POO that the defendants must have the mutual intention to assist each other, by force if necessary, against any person who might oppose them in the execution of the common purpose? Question 2a Whether the doctrine of joint enterprise applies to the offences under sections 18 and 19 of the POO? Question 2d Whether a person could be found guilty of riot without specific conduct on his part falling under the prescribed conduct provided in sections 18 and 19, but merely by virtue of alleged encouragement through his presence? On the substantial and grave injustice ground, whether a material irregularity arises in that the indictment does not mention any potential participants other than the co-defendants who were not convicted. Annex 2 Question 1 (1) “For the offences of unlawful assembly and riot respectively under sections 18 and 19 of the Public Order Ordinance, Cap 245, whether the common law doctrine of joint enterprise as elucidated in HKSAR v Chan Kam Shing (2016) 19 HKCFAR 640 is applicable?” (“Question 1”), and Question 2 (2) “If Question 1 is answered in the affirmative, for the offences of unlawful assembly and riot, whether the principle that a defendant’s presence at the scene is not always necessary for criminal liability under the common law doctrine of joint enterprise as enunciated in Sze Kwan Lung & Others v HKSAR (2004) 7 HKCFAR 475 is applicable?” (“Question 2”) [1] Cap 245. [2] HCCC 408/2016 (18 May 2018). [3] Poon CJHC, Chu and Pang JJA, cited as HKSAR v Leung Tin Kei [2020] HKCA 275 (29 April 2020) (“CA-Lo Case”). [4] Ribeiro Ag CJ, Fok PJ and Stock NPJ [2021] HKCFA 17 (17 May 2021). [5] (2020) 23 HKCFAR 518 see §§87-97. [6] [2020] HKDC 588 (24 July 2020). [7] Cap 221. [8] Poon CJHC, Macrae VP and A Pang J, cited as Secretary for Justice v Tong Wai Hung [2021] HKCA 404 (25 March 2021) (“CA-Tong Case”). [9] [2021] HKCA 807 (7 June 2021). [10] Annex 1, Questions 1a to 1d. [11] Ibid Question 2a; Annex 2, Questions 1 and 2. [12] Ibid Question 2d. [13] Annex 1. [14] [1891] AC 107 at 144-145. In a criminal law context, see also R v Fulling [1987] QB 426 at 431-432; R v Smurthwaite (1994) 98 Cr App R 437 at 440; and R v Platt (2016) 1 Cr App R 22 at §27. [15] [2021] HKCFA 24 at §17. [16] [2021] HKCFA 24. [17] Ibid at §§37 and 40. [18] Appearing for Lo with Mr Lawrence Lau, Mr Kin Lau and Mr Jason Ko. [19] Sitting as an additional Judge of the Court of First Instance, on an appeal by way of case stated [2012] 5 HKLRD 556. [20] Ibid at §19. [21] Ibid at §§22 and 83. [22] See §§68-70 below. [23] Section E of this judgment. [24] See §§68-70 below. [25] CA-Lo Case at §24. [26] CA-Tong Case at §§35-36. [27] In Sections C.4 to C.7 below. [28] Examples taken from R v Caird (1970) 54 Cr App R 499 and R v John McKinsie Jones (1974) 59 Cr App R 120 discussed in Section B.1 below. [29] CA-Lo Case at §§51-63. [30] (1888) 16 Cox CC 420. Along the same lines, see Tse Chung v R [1967] HKLR 452 at 455-456, per McMullin J. [31] Ibid at 432. [32] [1907] 2 KB 853. [33] Ibid at 860. [34] Ibid. [35] (1970) 54 Cr App R 499. [36] Ibid at 506. [37] (1974) 59 Cr App R 120 at 127. [38] Anderson v A-G (NSW) (1987) 10 NSWLR 198. [39] Ibid at 113. [40] Ibid at 114-115. [41] Law Com No 123 (24 October 1983) at §5.2. [42] Criminal Law, 4th ed, (1978) p 750. [43] Section 1(1): “Where 12 or more persons who are present together use or threaten unlawful violence for a common purpose and the conduct of them (taken together) is such as would cause a person of reasonable firmness present at the scene to fear for his personal safety, each of the persons using unlawful violence for the common purpose is guilty of riot.” ... (3): “The common purpose may be inferred from conduct.” [44] While such changes were made against the background of the extremely serious riots in 1967, the legislation had apparently been in preparation for some two years previously: Second Reading of the Bill, Official Report of Proceedings of the Legislative Council 15 November 1967, p 474. The POO came into force on 17 November 1967. [45] Sir Denys Roberts, later Mr Justice Roberts NPJ. Official Report of Proceedings of the Legislative Council 1 November 1967, pp 438 and 440. [46] Ibid, p 444at §9. The Explanatory Memorandum of a Bill, including its Objects and Reasons, is admissible for ascertaining the statutory purpose: See HKSAR v Cheung Kwun Yin (2009) 12 HKCFAR 568 at §§12-14; HKSAR v Li Kwok Cheung George (2014) 17 HKCFAR 319 at §37; and, most recently, Secretary for Justice v Leung Kwok Hung [2021] HKCFA 32 at §25. [47] [2012] 5 HKLRD 556. [48] Ibid at §19. [49] Ibid at §21. He added that in such a case, such persons might each be separately guilty of an offence under POO section 17B. [50] Ibid at §22. [51] CA-Lo Case at §26. [52] Ibid at §§57-61. Lam JA’s approach was also cited with approval by the Court of Appeal in CA-Tong Case at §63. [53] Ibid at §58. [54] Ibid at §61. [55] Ibid at §§59 and 60. [56] (2016) 19 HKCFAR 640 at §41. [57] Brown & Anor v The State (Trinidad And Tobago) [2003] UKPC 10 at §13. [58] HKSAR v Chan Kam Shing (2016) 19 HKCFAR 640 at §§33 and 63. [59] Ibid at §§41-44, 63. [60] Ibid at §§45-56, upholding the Privy Council’s decision in Chan Wing Siu [1985] 1 AC 168; and declining to follow R v Jogee [2017] AC 387. The narrow view adopted in the UK in Jogee that the intent must be both shared and specific, is not part of the law of Hong Kong. [61] Ibid at §98. [62] Crimes Ordinance (Cap 200) sections 159A and 159C (conspiracy); sections 159G(1) and 159J(1) (attempts). Incitement is punishable at common law. [63] See CA-Lo Case at §26. [64] CA-Lo Case at §23. [65] CA-Tong Caseat §§4-5, 19-24. [66] Ibid at §56. [67] CA-Lo Case at §24. [68] CA-Tong Case at §§35-36. [69] HKSAR v Chan Kam Shing (2016) 19 HKCFAR 640 at §6. [70] Sze Kwan Lung v HKSAR (2004) 7 HKCFAR 475 at §37 (offences of manslaughter and arson). [71] (2016) 19 HKCFAR 640 at §§8-14. [72] Ibid at §12. [73] Cited at §61 above. [74] Section 90(1): “If a person has committed an arrestable offence, any other person who, knowing or believing him to be guilty of the offence or of some other arrestable offence, does, without lawful authority or reasonable excuse, any act with intent to impede his apprehension or prosecution shall be guilty of an offence.” [75] As was acknowledged by Mr Anthony Chau, DDPP (Ag) appearing for the Respondent with Mr Ivan Cheung, SPP, Ms Karen Ng, PP and Mr Wilson Lam PP. [76] CPO, section 89 and Crimes Ordinance (Cap 200) sections 159A, 159C, 159G(1) and 159J(1). [77] (2020) 23 HKCFAR 518 at §90. [78] CA-Tong Case at §56. [79] HKSAR v Chan Kam Shing (2016) 19 HKCFAR 640 at §10. [80] (1994) 74 A Crim R 1 at 6. [81] See R v Atkinson (1869) 11 Cox CC 330 at 332; Anderson v A-G (NSW) (1987) 10 NSWLR 198 at 212; Boxer v R (1995) 81 A Crim 299 at 310. [82] (1810) 2 Camp 358 at 370; 170 ER 1183 at 1187. [83] (1970) 54 Cr App R 499 at 505. [84] (1994) 74 A Crim R 1 at 8-9. [85] [1982] QB 416. [86] Ibid at 427. [87] [2007] 2 AC 105 at §§27-28. Cited in Chow Nok Hang (2013) 16 HKCFAR 837 at §77. [88] [1982] QB 416 at 426. [89] (1989) 88 Cr App R 317. [90] Ibid at 319-320. [91] Ibid at 321. [92] CA-Lo Case at §13. [93] Ibid at §14. [94] Ibid at §37. [95] Ibid at §39. [96] (1989) 154 JP 201. [97] Ibid at 203-204. [98] Ibid at 204. [99] Reflected in Questions 1a-1d of Annex 1. [100] Section B.2 of this judgment. [101] As reflected in Questions 2a and 2d of Annex 1. [102] Sections C.8 and D of this judgment.