Sch THIRD para 6
For the purposes of this Schedule a notice may be served— (i) by registered post or by delivery to or at the residence of the person to whom it is addressed; or (ii) if the responsible authority are unable after reasonable enquiry to ascertain the name and address of the person upon whom' it should be served, by addressing it to him— (a) by name, if his name is known; or (b) if his name is not known, by the description of " owner" or " occupier " of the premises (naming them) to which it relates, and by delivering it to some person on the premises, or, if there is no person on the premises to whom it can be delivered, by affixing it or a copy thereof to some conspicuous part of the premises.