Subject to any rules made in this behalf, any officer of the Board generally or specially authorised by the Board in this behalf, may, at all reasonable times, enter upon any land or premises and there do such things as may be reasonably necessary for the purpose of lawfully carrying out any of its works or of making any survey, examination or investigation, preliminary or incidental to the exercise of powers or the performance of the functions by the Board under this Act:
     Provided that no such officer shall enter any building or any enclosed court or garden attached to a dwelling house, unless with the consent of the occupier thereof, without previously giving such occupier at least seven days' notice in writing of his intention to do so.