User of land and buildings in contravention of plans

After the coming into operation of any of the plans in a zone no person shall use or permit to be used any land or building in that zone 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 by regulations made in this behalf, any land or building for the purpose for, and the extent to which it is being used upon the date on which such plan comes into force.