'Public interest' is a wide concept involving what is a legitimate concern to the public. Instances include the conduct of people holding public office, the conduct of a political party, the conduct of a clergyman and artistic works such as plays and books. It extends as far as the criticism of a restaurant's food in a newspaper review.
The Defamation Act 2005 s.29 provides a defence of honest opinion where the expression of opinion is related to a matter of public interest and based on ‘proper material’ that is substantially true or based on privileged material.
The "Public Interest" factor seems to be the 'common factor' in common and criminal law.
Sadly the 'Public Interest' factor also seems to have been blurred and lost in the mist over the last thirty to forty years, maybe that is why in 'today's world' we need a Wikileaks etc to 'keep the bastards honest'!
It is also interesting to note how the "model litigators" all profess to adhere to the principle of the 'Public Interest' in their publically available fluffy (K's phrase that is apt) documentation/governances (see CDPP example here:
http://www.cdpp.gov.au/Publications/...tionPolicy.pdf ), yet when it comes to practise they all go into damage control, or ego mania, or "it wasn't me officer", or (like MT in another thread) bury their head in the sand!
Hey Mick T this is for you mate, from Sophocles god bless his soul:
"The kind of man who always thinks that he is right, that his opinions, his pronouncements, are the final word, when once exposed shows nothing there. But a wise man has much to learn without a loss of dignity."