Relevant principles
20The general principle was stated by Gibbs ACJ in Sankey v Whitlam [1978] HCA 43; (1978) 142 CLR 1 at 38-39.
"The general rule is that the court will not order the production of a document, although relevant and otherwise admissible, if it would be injurious to the public interest to disclose it. However the public interest has two aspects which may conflict. These were described by Lord Reid in Conway v. Rimmer (43), as follows:
'There is the public interest that harm shall not be done to the nation or the public service by disclosure of certain documents, and there is the public interest that the administration of justice shall not be frustrated by the withholding of documents which must be produced if justice is to be done.'
It is in all cases the duty of the court ... to decide whether a document will be produced or may be withheld. The court must decide which aspect of the public interest predominates, or in other words whether the public interest which requires that the document should not be produced outweighs the public interest that a court of justice in performing its functions should not be denied access to relevant evidence. In some cases, therefore the court must weigh the one competing aspect of the public interest against the other, and decide where the balance lies."
21As is pointed out in Alister v The Queen [1984] HCA 85; (1984) 154 CLR 404, where a party seeks the production of and access to documents in respect of which a claim to immunity is made, the party seeking access first must demonstrate a legitimate forensic purpose for having the documents produced. It is only in the event that such a purpose is demonstrated, that both aspects of the public interest require consideration by the undertaking of the balancing exercise and, when doing so, the Court may inspect any documents produced: Alister v The Queen at 412, 414, 438-439, 456; Air Canada v Secretary of State for Trade [1983] 2 AC 394 at 436, 439; R v Saleam (1989) 16 NSWLR 14 at 18-19; Attorney-General for New South Wales v Stuart (1994) 34 NSWLR 667 at 675-676, 681, 690.
22It has long been recognised that there is a public interest in the protection against disclosure of the identity of police informers. The leading English cases include Marks v Beyfus (1890) 25 QBD 494 and D v National Society for the Prevention of Cruelty to Children [1978] AC 171. In the latter case the practice which had developed by the time of Marks v Beyfus was described as having hardened "into a rule of law" that the informer's identity should not be disclosed "except where upon the trial of a defendant for a criminal offence disclosure of the identity of the informer could help to show that the defendant was innocent of the offence": per Diplock LJ at 218.
23In Cain v Glass (No. 2) (1985) 3 NSWLR 230, McHugh JA (with whom Kirby P agreed on this question) said of that rule (at 248):
"... the courts in this State should continue to apply the rule that no question of weighing competing public interests arises when a claim is made that the name of a police informer should be disclosed. The rule is absolute and is relaxed only 'where upon the trial of a defendant for a criminal offence disclosure of the identity of the informer could help to show that the defendant was innocent of the offence'. I have stated the exception in the language of Lord Diplock in D v National Society for the Prevention of Cruelty to Children (at 218). In the same case Lord Simon of Glaisdale said (at 232) that the sources of police information 'must be forthcoming when required to establish innocence in a criminal trial."
Priestley JA considered (at 242-243) that the court was still required to undertake a balancing exercise of the competing interests.
24As this passage from McHugh JA's judgment shows, the exception to the informer rule has been described in different ways. In Marks v Beyfus Lord Esher MR (with whom Lindley LJ agreed) described it (at 498) as being that disclosure should be made where the judge is of the opinion that "it is necessary or right in order to shew the prisoner's innocence". Bowen LJ (at 500) said the exception applied when the judge "saw that the strict enforcement of the rule would be likely to cause a miscarriage of justice" because of the risk of innocent people being convicted.
25In DPP v Smith (1996) 86 A Crim R 308 this Court said (at 311-312) with reference to these cases that there was powerful authority for the proposition that, at common law, when a claim for immunity from production is made in respect of the identity of a police informer, the court before whom the claim is made does not undertake for itself, afresh, a balancing exercise, weighing one interest against the other because that balance has already been struck and is reflected in the various statements of the exception to the rule.
26As this Court also noted in DPP v Smith , there are contrary views as to the extent to which a weighing of the competing interests is still required when a claim is made to protect the identity of a police informer. Those contrary views have been stated in this Court: see R v Meissner (1994) 76 A Crim R 81 at 88; and in other intermediate appellate courts: see Jarvie v Magistrates Court of Victoria at Brunswick [1995] 1 VR 84 at 89-90; R v Werner Paul Roberts [2004] VSCA 1; (2004) 9 VR 295 at [103]; Haydon v Magistrates Court of South Australia [2001] SASC 65; (2001) 87 SASR 448 at [13]-[18]; R v McKelliff [2004] SASC 63; (2004) 87 SASR 476 at [20]-[27]; and Australian Securities and Investment Commission v P Dawson Nominees Pty Ltd [2008] FCAFC 123; (2008) 247 ALR 646 at [22]-[28]. It is not necessary in this case to resolve these different views because on either approach the primary judge erred in the exercise he undertook.
27As Doyle CJ notes in Haydon v Magistrates Court of South Australia (at [17]), on either approach the court is required to make an assessment of the significance to the defence case of the material which identifies the police informer and the need to disclose his or her identity. In DPP v Smith (at 311-312) the rule was described as requiring non-disclosure except where disclosure could help show that the accused is not guilty. In Jarvie v Magistrates Court of Victoria , Brooking J considered (at 89-90) that the balance would incline in favour of disclosure once it was demonstrated that "there is good reason to think that disclosure of the informer's identity may be of substantial assistance to the defendant in answering the case against him". The latter formulation was adopted in R v Meissner at 88; R v Mason (2000) 77 SASR 105 at [36]-[45]; Haydon v Magistrates Court of South Australia at [29]-[31], [118]; and R v McKelliff at [26].
28An assessment of the significance of the material which identifies the police informer directs attention to why disclosure is required to avoid the likelihood of substantial prejudice to the accused. The circumstances in which that may be the case include that mere disclosure of the identity of the informer will help to show that the accused is innocent, that disclosure is necessary to adduce evidence of information which will help to show that the accused is innocent and that disclosure will lead to the production of other evidence which will have that consequence: Cain v Glass (No. 2) at 250-251; R v Mason at [38]-[44].
29Another factor to be taken into account, when addressing the exception to the rule and balancing the competing public interests, is the stage which the criminal proceedings have reached. In Cain v Glass (No. 2) the question was whether the exception applied to committal proceedings. McHugh JA (with whom Kirby P agreed) concluded (at 251) that the rule applied "at all stages of criminal proceedings" including the committal stage and that "(r)ejection of the claim at one stage will not preclude an application at a subsequent stage". At each stage it was necessary to consider the question being addressed and whether, in that context, disclosure of an informant's identity would assist the defendant. At the trial stage it is sufficient to require disclosure "that the jury might reasonably think that the evidence which is likely to result from the disclosure, will lead to an acquittal" (at 251).
30The authorities also make clear that for the non-disclosure rule to apply or the public interest against disclosure to prevail, it is not necessary to show the existence of any real or imminent threat or danger to the particular informer in the event of disclosure. That is because the public interest and rationale for the rule is to ensure that sources of information which assist police in discharging their duty of preventing and detecting crime do not dry up: D v National Society for the Prevention of Cruelty to Children at 218, 232; Cain v Glass (No. 2) at 233-234, 247; DPP v Smith at 311. That interest is put at risk if the anonymity of those sources is not respected and protected. In R v Mason Bleby J noted (at [29]-[31]) that the existence of a threat to the informer is not a condition precedent to the operation of the informer rule. The same point was emphasised by McHugh JA in Cain v Glass (No. 2) (at 253-254) when addressing whether it was relevant to consider the safety of police informers who were witnesses:
"... the anonymity of the informants is entitled to be protected whether or not they are likely to be in danger. It is precisely because informants may often be in danger that the public interest requires that their anonymity should be protected. It is not for individual judges or magistrates to weigh up the competing public interest. The law has already done so. The public interest always requires the protection of the informant unless disclosure will assist in the protection of the liberty of the subject in criminal proceedings."