(1) Where any land situated in any area is required by the master plan or a zonal plan to be kept as an open space or unbuilt upon or is designated in any such plan as subject to compulsory acquisition, then if at the expiration of five years from the date of operation of the plan under section 11 or where such land has been so required or designated by any amendment of such plan, from the date of operation of such amendment, the land is not compulsory acquired, the owner of the land may serve on the Government a notice requiring his interest in the land to be so acquired.
(2) If the Government fails to acquire the land within a period of six months from the date of receipt of the notice, the master plan or, as the case may be, the zonal plan shall have effect after the expiration of the said six months as if the land were not required to be kept as an open space or unbuilt upon or were not designated as subject to compulsory acquisition.