What is the test for the defence of privilege in a defamation case?

It is important to note that the plaintiff must show that malice is the dominant purpose of the communication if the defence of privilege is to be defeated. People can act on a variety of motives, some more pure than others and a court should not too readily impute the worst of these motives to a party acting on an occasion of privilege. In Horrocks v. Lowe, [1975] A.C. 135, Lord Diplock made the following observation at p. 150-51: Judges and juries should, however, be very slow to draw the inference that the defendant was so far actuated by improper motives as to deprive him of the protection of the privilege unless they are satisfied he did not believe what he said or wrote was true or that he was indifferent to its truth or falsity. The motives with which human beings act are mixed. They find it difficult to hate the sin but love the sinner. Qualified privilege would be illusory, and the public service that it is meant to serve defeated, if the protection which it affords were lost merely because a person, although acting in compliance with a duty or in protection of a legitimate interest, disliked the person whom he defamed or was indignant at what he believes to be that person’s conduct and welcomed the opportunity of exposing it. It is only where his desire to comply with the relevant duty or to protect that legitimate interest plays no significant part in his motives for publishing what he believes to be true that express malice can properly be found.