Mamman v. Salaudeen  13 NWLR (Pt. 958) 478 at 507-508, paras. H-C, Onnoghen J.S.C.:
The full Judgment is available here.
A closer look at the rule set down by Kopes, L.J. would reveal that it is not every letter written by a lawyer in the course of his legal duties to his client that is privileged. The rule requires that the communication must be reasonably necessary and usual in the discharge of his duties, and in the interest of his client. In other words, if the communication is not reasonably necessary (even being merely necessary may not suffice) and was not in the usual discharge of his duties (that is, for other personal purposes) and was not in the interest of his client (a lawyer should naturally act in his client’s interest), then the communication may not be privileged as the lawyer may be liable to a claim in defamation.