What is the scope of response permitted under the defence of qualified privilege?

As for the scope of response permitted under the defence of qualified privilege, the court quoted Lord Atkinson in Adam v. Ward, [1917], A.C. 309., at p. 339, as follows: ... a person making a communication on a privileged occasion is not restricted to the use of such language merely as is reasonably necessary to protect the interest or discharge the duty which is the foundation of his privilege; but that, on the contrary, he will be protected, even though his language should be violent or excessively strong, if, having regard to all the circumstances of the case, he might have honestly and on reasonable grounds believed that what he wrote or said was true and necessary for the purpose of his vindication, though in fact it was not so.