It definitely varies from council to council. We are an agricultural holding so for most things we don't need PP, but because of a very tricky neighbour who puts in complaints about anything that anyone within a several mile radius does, we were advised to apply for Approval (rather than PP - the difference is that Approval doesn't take long and doesn't cost much, nor do you require full drawings (here anyway)
When we first came to live here, we didn't need permission or approval for anything unless to do with the house. Now all has changed.
When the chappie came from the council to view where we intended to put up our shed (it's a bit bigger than many sheds
) he signed off without a murmur, and said "whilst I'm here, is there anything else you want to do?" So I mentioned we still needed a handful more sheep shelters, he glanced at what we already have and gave his approval immediately (our shelters are sturdy, with a straining post at each corner, so definitely not mobile).
So councils can be helpful, but I know from others experiences that they can also be bolshie. Good luck with navigating the planning laws.