16. Any notice or certificate to be given under these Regulations may be given—
(a)by delivering it to that person; or
(b)by leaving it or sending it in a prepaid letter addressed to him, at his usual or last known residence; or
(c)in the case of an incorporated company or body, by delivering it to their secretary or clerk at their registered or principal office, or by sending it in a prepaid letter addressed to him at that office.