Public interest immunity and judicial deference

The puzzle underlying the law of public interest immunity (PII) is well known. In ordinary proceedings all relevant evidence should be placed before the court and the parties, including when the government is one of those parties. 1 But what if some of the relevant evidence – due to reasons in the public interest – cannot be disclosed to the other parties involved? 2 The traditional way in which English law tackles this puzzle is by invoking the law of PII. Ever since the landmark decision in Conway , it has been settled that ‘the courts should balance the public interest in the proper administration of justice against the public interest in withholding any evidence which a Minister considers ought to be withheld’. 3 If the public interest favours disclosure of the evidence, the evidence is admitted and made ‘available to both parties and to the court’; but if the contrary is true the evidence will be excluded altogether from the proceedings and made ‘available neither to the other parties nor to the court’. 4