Retrospective could cost a lot of money if they want to get bloody with you.
Cherwell Council made a man with big balls take a decent building down near here a few years ago.
Frankly, the sort of outfit that are able to do what you want, you really dont want anyway.
Retrospective cost the same as if you apply before building
It’s appeals if you get turned down that can cost big money, no more or less likely to get turned down retrospectively than before building, it’s the same process