Nothing in this Act contained shall authorize any person to purchase, take, use, or interefere with any land, soil, or water, or any right in respect thereof, or to take away, lessen, prejudice, or alter any of the rights, privileges, powers, or authorities, vested in or enjoyed by Her Majesty’s Principal Secretary of State for the War Department for the time being, without the previous consent of the same Principal Secretary signified in writing under his hand, which consent the said Principal Secretary for the time being is hereby authorized to give.