If any such Obstructions or Projections were erected or placed against or in front of any House or Building in any such Street before the passing of the special Act, the Commissioners may cause the same to be removed or altered as they think fit; provided that they give Notice of such intended Removal or Alteration to the Occupier of the House or Building against or in front of which such Obstruction or Projection shall be Thirty Days before such Alteration or Removal is begun, and, if such Obstructions or Projections shall have been lawfully made, they shall make reasonable Compensation to every Person who suffers Damage by such Removal or Alteration.