Public interest immunity

Public-interest immunity (PII) is a principle of English common law under which the English courts can grant a court order allowing one litigant to refrain from disclosing evidence to the other litigants where disclosure would be damaging to the public interest. This is an exception to the usual rule that all parties in litigation must disclose any evidence that is relevant to the proceedings. In making a PII order, the court has to balance the public interest in the administration of justice (which demands that relevant material is available to the parties to litigation) and the public interest in maintaining the confidentiality of certain documents whose disclosure would be damaging. PII's have been used in criminal law against large organised criminal outfits and drug dealers where the identity of paid police informants could be at risk.

An order that PII applies would usually be sought by the British government to protect official secrets, and so can be perceived as a gagging order. Where a minister believes that PII applies, he signs a PII certificate, which then allows the court to make the final decision on whether the balance of public interest was in favour of disclosure or not. Generally, a court will allow a claim of PII without inspecting the documents: only where there is some doubt will the court inspect the documents to decide whether PII applies.

Originally, a government minister was under a duty to advance a PII point where PII could be relevant, and the court took a certificate from a minister claiming PII as final and conclusive. However, over time, there has been an increase in both the ability of a minister to make a disclosure, notwithstanding the potential application of PII, and the ability of the courts to review a claim of PII. In Conway v Rimmer [1968], the House of Lords held that the courts retained the final decision on whether PII should be upheld, and, in R v Chief Constable of West Midlands, ex parte Wiley [1995], the House of Lords decided that a minister could discharge his duty by making his own judgment of where the public interest lies (that is, to disclose or to assert PII). In practice, this is thought to have led to a reduction in the number of cases when PII is asserted.

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