If the owner of a building on or to whom a notice was served or delivered, fails to resume or to complete the erection of such building within the periods specified in such notice and the local authority in question is of the opinion that such building is unsightly or dangerous to life or property or derogates from the value of adjoining or neighbouring properties, such local authority may by notice in writing, served by post or delivered, order such owner to demolish such building, to remove the material of which such building consisted and any other material or rubbish from the site in question, and to otherwise clean up such site.