8E+WWithout prejudice to any other mode of service, a completion notice may be served on a person—
(a)by sending it in a prepaid registered letter, or by the recorded delivery service, addressed to that person at his usual or last known place of abode or, in a case where an address for service has been given by that person, at that address;
(b)in the case of an incorporated company or body, by delivering it to the secretary or clerk of the company or body at their registered or principal office or sending it in a prepaid registered letter or by the recorded delivery service addressed to the secretary or clerk of the company or body at that office; or
(c)where the name or address of that person cannot be ascertained after reasonable inquiry, by addressing it to him by the description of “owner” of the building (describing it) to which the notice relates and by affixing it to some conspicuous part of the building.