Planning Permission vs Building Control

I received planning permission for a house. This house design had a stairs with a winder in the middle. We built the house. Building Control now say it is not acceptable as winders if not avoided should be at the bottom. But I got planning permission so how can it now be wrong?. Part B (which I am now aware of) uses the word preferably in relation to not using a winder, can this become never at the stroke of a pen?