It shall be lawful for any person authorised by the competent authority in this behalf to enter into or upon any building or land in a slum area with or without assistants or workmen in order to make any inquiry, inspection, measurement, valuation or survey, or to execute any work which is authorised by or under this Act or which it is necessary to execute for any of the purposes or in pursuance of any of the provisions of this Act or of any rule or order made thereunder.