I think one of the obvious things here is also where the thing is placed.  If you are in the middle of an area which is undergoing lots of building then you may have probs, if not, if you are in the back of beyond then build what you feel like as chances are no one will ever say anything.  

BUT they can do.  If you are in the middle of doing whatever you have decided to do and the forestals (forest police) turn up they will ask for permissions and all that.  If you don't have them you will have a building inspector there the next day and the police who are there to take away your cement mixer etc so you have to stop.  

Everybody has always ignored building regs and will continue to do so I suppose.  But now the difference is nothing illegal will ever become so (or at least that is what I am told).  Not a problem then all steam ahead but it will also never feature on the deeds of the land, can't be legally sold, can't be mortgaged and will not be respected if the council wants to build a road or something.