Application to replace extant PP vs new application?

[cjard]

My building has planning permission for change of use, but I want a different set of plans (still a change of use, but a very different layout). The difference between the two is large and the LPA advise a new application is required

To submit an app for 2 dwellings is £770, but I note in the fee structure there is a "New application to replace extant" at £500

My question is, when does the new application replace the existing permission?
When it's submitted (i.e. it's £270 cheaper, but it kills an approved PP, it might then be refused, leaving a building with no PP) or
When it is decided? (i.e. it will only replace the existing PP if it is approved, so the building will only have one approved plan whereas if I pay the extra £270, the new passes, then there's a choice of schemes to implement?)

In my logic, I think it should be the latter, that the new app doesn't kill the old app unless the new app passes..

 

[DevilDamo]

Basically, you have a current planning approval. You wish to make changes to the drawings, which are normally covered by a "Non-material amendment" application form. However, if the LPA decide the amendments are too significant, then they can request a new "Full" application be submitted. So the only choice you have is to submit a Full application. It would go in your favour that an existing permission is still intact. If the new application is refused, you still have the old approval to fall back on.

The "New application to replace extant" application is as it states... to replace an existing that is due to expire. It would normally be a like for like replacement and maybe minor changes could be incorporated. But this form cannot be used as the changes are not minor.