My questions are:
1. Is it possible to get round permitted development rules by renting additional land to make it up to 5 hectares?
2. Does anyone know the rules around creation of a hardstanding under PD?
3. If we build a "hay storage shed" then later start using it for housing animals is this likely to be an issue?
4. What are the rules about having a crappy caravan for storage and somewhere to make a cup of tea/get out of the rain? Similarly if I wanted to store a livestock trailer there is that allowed?
1. Yes. When I applied, all I had to do was state the size of my holding, and did not have to specify if owned or rented.
2. Depends how much hardstanding you want, and if anyone's going to notice.
3. No. It's what most people do to get animal housing because if you initially state that you are planning to put animals in, then there are more regulations involved. Put animals in later and no one local can remember what you actually applied for initially and so it becomes accepted.
Unless you keep your animals so close to someone's house that they become a nuisance and trigger a complaint. If the complaint is unreasonable (ie your building is say 100yds from their house) you put in planning permission for change of use. This is generally easier to get than applying for animal housing in the first place, as you have already achieved getting the building, so even if animal use is refused, then you still have the building.
4. Technically even a mobile building requires planning permission(although people will tell you otherwise) But in practice, if it's not an absolute eyesore and looking like an encampment, and no one complains, then it is usually tolerated and the planners don't bother.