There has been a huge amount of authoritative commentary on the issue of disclosure in the aftermath of “near misses” like the Liam Allan case. Sadly, in the absence of the scrutiny that followed his case and others, it is unlikely there would be any significant response from those who are responsible for the investigation and prosecution of criminal offences. If, as the review following Mr Allan’s case found, it is an issue of “lack of knowledge” then this is a symptom of the system and not an isolated case. But this article looks at the discrete issue of what is known loftily as the doctrine of Public Interest Immunity, or PII; an area of the law of evidence characterised by some of the gravest miscarriages of justice in this country for decades.

It is a halting observation of the doctrine that it is in fact the permissible suppression of relevant evidence by the state to the accused. The operation of the doctrine is only triggered where the threshold for disclosure is otherwise met and applies where the public interest in not making disclosure outweighs the interests of the accused in having full disclosure. Surprisingly its origins are civil, not criminal law, although its use in the latter has proliferated and greatly overshadows its use in the former. It is an exceptional remedy but this exceptionality has been normalised through over use.

One of the leading cases in its evolution was R v Davis, Rowe and Johnson [1993] 1 WLR 613 (otherwise know as the M25 three) – a murder case – where the state failed to disclose the fact that an informer was paid in excess of £10,000 by the police for information implicating the accused. The convictions were later quashed. (Mr Rowe went on to have a successful career as a BBC journalist). An earlier case, Judith Ward (1992) 96 Cr App R 1, unquestionably wrongly convicted of the M62 bombings, resulted in the requirement that the judge, not prosecutor should decide whether PII should be granted in criminal proceedings.

PII has had a chequered past before the European Court of Human Rights. Over the years, since Ward and other cases, the principles have developed and the procedure set down in part in legislation and the Criminal Procedure Rules.

In the United Kingdom, the leading case remains R v H; R v C [2004] UKHL 3. This offers a series of possible solutions where the state wish to suppress ordinary disclosure whilst achieving fairness to the defence, including the provision of summaries of sensitive intelligence, redacted documents or the appointment of a special advocate. Where none of these solutions are practicable, then either disclosure must be made or the proceedings discontinued. The option of dropping a case may seem extreme but it does happen, even in the most serious of cases, including terrorism: see for example the recent Northern Irish case of Duffy.

Where an order is made, a critical safeguard is the duty on the part of the prosecutor and judge to keep that decision under review. In light of the existing and seemingly systemic issues emerging around standard disclosure, it is probably a reasonable assumption to make that these are also likely to present in cases where PII is asserted.

Some fortification of this assumption can be found in the Crown Prosecution Service’s own guidance on PII in national security cases.

The position in relation to national security cases is different. The CPS website notes that “the preferred means by which [MI5, MI6 and GCHQ] seek to claim PII before a court” (emphasis added) is by way of Ministerial Certificate. Such a certificate – the issue of which has no statutory basis and has not so far been challenged domestically or before Strasbourg – requires the relevant Minister (the Secretary of State for the Home Department in the case of MI5 and for Foreign and Commonwealth Affairs in the cases of MI6 and GCHQ) to be satisfied that any disclosure “would cause real risk of serious prejudice to an important public interest”. The certificate is placed before the trial judge, usually at a type three hearing. In Guardian News and Media Ltd & Ors v Incedal [2014] EWCA Crim 1861 (in the context of in camera proceedings) the Lord Chief Justice held that the court will “pay the highest regard” to what the Secretary of State says in the certificate on national security issues providing there is an evidential basis for it. For more reflections on Incedal see here. National security is an issue for the executive; Secretary of State for the Home Department v Rehman [2003] 1 AC 153; determining whether there is evidence supporting the view and whether open justice should be fettered are decisions for the judiciary. Again, this is the position in principle; practice is likely to vary in different Crown Courts throughout the country. It is noteworthy that if the prosecutor makes the application (and it is envisaged by the CPS it may not always be the prosecutor who does so) he or she is merely trustee for the material, which “must be returned to the [intelligence] Agency after the hearing”. How the on-going review – the critical safeguard – of the material can take place effectively in such circumstances is difficult to envisage.

What is clear is that in the face of catastrophic failings within a transparent and accountable legislative framework, it is likely similar concerns pervade the darker corners of disclosure in the criminal justice system, particularly when that most formless of legal concepts, national security, is at large.