Subject to any rule made in this behalf, any person, generally or specially authorised by the Board in this behalf, may, whenever it is necessary so to do, for any of the purposes of this Act, at all reasonable times, enter upon any land or premises and make any inspection or inquiry or do such other act or thing as may be prescribed:

Provided that no such person shall enter any building or any enclosed courtyard or garden attached to a dwelling-house (unless with the consent of the occupier thereof) without previously giving such occupier at least twenty-four hours notice in writing of his intention to do so.