A communication that does not fit into one of the class privileges may nonetheless be protected under the "case-by-case privilege" on an ad-hoc basis where the requisite criteria are met.
Case-by-case privilege can be invoked where:
- the communication originates in a confidence that the identity of the informant will not be disclosed;
- the confidence is essential to the relationship in which the communication arises;
- the relationship is one which should be sedulously fostered in the public good; and
- the public interest in protecting the identity of the informant from disclosure outweighs the public interest in getting at the truth.
Confidentiality of journalistic sources can be measured on a case-by-case basis based on the "Wigmore criteria". Where appropriate, "the courts will respect a promise of confidentiality given to a secret source by a journalist or an editor. However, where the public's interest in protecting sources is outweighed by other interests promises of secrecy cannot be maintained."
The fourth criteria of the test has found not be made out where a journalist would not reveal a source who had potentially forged documents implicating a former prime minister in a illegal transaction.
R v National Post,  1 SCR 477, 2010 SCC 16 (CanLII)
see "case-by-case privilege" above
- R v National Post, ibid.
National Post, ibid.