Revert to a previous planning approval - Public forum - Planning Advisory Service (PAS)

One planning application has been approved and mostly completed;  some time later a new application is made and approved which changes the design of the residue of the first application.  For that residual work, does the NEW approval supersede and cancel the first approval, OR is it acceptable to revert to the first-approved design and complete it without further consultation (ie, can you ignore the second approval and complete the work according to the first approved application)?