Development plan prepared prior to the application of this Act to be deemed development plan under this Act

If any local authority has bccn declared as a planning authority for a pliinning iunen and he local aulhoi-ity has prcpared a developn~enl plan for the pliulnin: area beforc thc application of this Act to ha^ area, the develop~ncnt pliin already prepared may bc deemed to be a development plan under seclion 18 or seclion 19 of this Act.