Subject to the provisions of this section, any notice or other document required or authorised to be served or given under this Act may be served or given either—
Where the notice or document is required or authorised to be served on any person as having an interest in premises, and the name of that person cannot be ascertained after reasonable inquiry, or where the notice or document is required or authorised to be served on any person as an occupier of premises, the notice or document shall be taken to be duly served if—
Where the notice or other document is required to be served on or given to all persons having interests in, or being occupiers of, premises comprised in any land, and it appears to the authority required or authorised to serve or give the notice or other document that any part of that land is unoccupied, the notice or document shall be taken to be duly served on all persons having interests in, and on any occupiers of, premises comprised in that part of the land (other than a person who has given to that authority an address for the service of the notice or document on him) if it is addressed to " the owners and any occupiers " of that part of the land (describing it) and is affixed conspicuously to some object on the land.