A defendant in a proceeding for libel or slander who has not by the defendant's defence alleged the truth of the statement complained of shall not, except by leave of the Court at the trial, give evidence in chief at the trial with respect to—
(a) mitigation of damages;
(b) the circumstances of publication; or
(c) the character of the plaintiff—
unless the defendant gives particulars of the evidence to the plaintiff by notice served not less than seven days before the trial.