Under common law, public-interest privilege prevents the compulsory disclosure of documents or information which is against the public interest.
The public interest in disclosure is the principle that a court of justice ought not be denied access to relevant information, and that the opposing party should have access to all relevant information to make their case.
The court may, of its own motion, prevent admission of evidence if it thinks it may disclose privileged information.
However, if the information has been published elsewhere this is a very strong factor towards the public interest of disclosure.
[5] When people seek to protect their narrow and private interests, it is called private-interest privilege.