[9] The expression in the public interest directs attention to that conclusion or determination which best serves the advancement of the interest or welfare of the public, society or the nation and its content will depend on each particular set of circumstances. There will, as in the present case, often be competing facets of the public interest that call for consideration when making a final determination as to where the public interest lies and these are sometimes loosely referred to, in my view, as opposing public interests. In the present case, broadly speaking, the competing aspects of the public interest include the benefits conferred on the public by the transparency of government processes and the need for confidentiality in certain circumstances.
[10] The expression the public interest is often used in the sense of a consideration to be balanced against private interests or in contradistinction to the notion of individual interest. It is sometimes used as a sole criterion that is required to be taken into account as the basis for making a determination. In other instances, it appears in the form of a list of considerations to be taken into account as factors for evaluation when making a determination. By way of example, town planning legislation frequently lists a number of factors that a local council or planning body is required to take into account when making a determination, with a concluding consideration being a generalised reference to the public interest and the circumstances of the case.
[11] The indeterminate nature of the concept of the public interest means that the relevant aspects or facets of the public interest must be sought by reference to the instrument that prescribes the public interest as a criterion for making a determination. In this respect, the well-known observations of Deane J in Sean Investments Pty Ltd v MacKellar (1981) 38 ALR 363 at 375 are apposite. In that case, his Honour was considering the different process of determining the relevant considerations to take into account in the exercise of a broad statutory discretion, however, the approach is relevant in the present case. His Honour said:
In a case such as the present, where relevant considerations are not specified, it is largely for the decision-maker, in the light of matters placed before him by the parties, to determine which matters he regards as relevant and the comparative importance to be accorded to matters which he so regards.
[12] The public interest is not one homogenous undivided concept. It will often be multi-faceted and the decision-maker will have to consider and evaluate the relative weight of these facets before reaching a final conclusion as to where the public interest resides. This ultimate evaluation of the public interest will involve a determination of what are the relevant facets of the public interest that are competing and the comparative importance that ought to be given to them so that the public interest can be ascertained and served. In some circumstances, one or more considerations will be of such overriding significance that they will prevail over all others. In other circumstances, the competing considerations will be more finely balanced so that the outcome is not so clearly predictable. For example, in some contexts, interests such as public health, national security, anti-terrorism, defence or international obligations may be of overriding significance when compared with other considerations.
13 "The public interest" is a nebulous concept unless given further content of a legally normative nature: Oshlack v Richmond River Council (1998) 193 CLR 72 at [30] per Gaudron and Gummow JJ. Much civil litigation concerns the public interest, including most constitutional and administrative law matters and some ordinary civil actions: Oshlack at [71] per McHugh J. If characterisation as public interest litigation were sufficient reason to depart from the usual order as to costs, that order would cease to be usual in large areas of litigation. The expression "in the public interest" requires a consideration of the subject matter, scope and purpose of the statutory enactment in which it is contained: O'Sullivan v Farrer (1989) 168 CLR 210 at 216 per Mason CJ, Brennan, Dawson and Gaudron JJ.