Uses of land and buildings in contravention of Plans

After coming into operation of any of plan in a sector, no person shall use or permit to use any land or building in that sector otherwise than in conformity with such plan : Provided that it shall be lawful to continue to use, upon such terms and conditions as may be prescribed, any land or building for and to the extent for and to which it is being used upon the purpose on the date on which such plan comes into force.