During the period of operation of this Act, no relief shall be available under the provisions of section 3 in respect of the following encroachment or unauthorised development, namely:--
         (a) encroachment on public land except in those cases which are covered under clauses (a), (b) and (c) of sub-section (1) of section 3;
         (b) removal of slums and Jhuggi-Jhompri dwellers, hawkers and urban street vendors, unauthorised colonies or part thereof, village abadi area and its extension, in accordance with the relevant policies approved by the Central Government for clearance of land required for specific public projects.