Once PP has been granted, the use of the land; buildings etc, is established and set forever........... or until another application is made and granted.
The only possible difficulty would be if certain conditions or "reserved matters" were attached. These have to be fulfilled within either 2,3 or 5 years, depending on a variety of considerations.
Have a close look at the original consent. Check for any of the above. That's the only way you'll find out where you stand.