A defendant in an action for defamation who does not plead the defence provided for by section 15 of the Defamation Act 1957 may not adduce evidence in chief, with a view to mitigation of damages, as to the circumstances under which the defamation was published or as to the character of the plaintiff, unless –

(a) the Court or a judge gives leave; or

(b) not less than 7 days before the trial, the defendant furnishes particulars to the plaintiff of the matters as to which the defendant intends to adduce evidence.