I am in Derbyshire too .....green belt land, so no way we can have any caravan to live in (except while renovating our farmhouse). Don't know where you are, but I think I am right in saying that you need a large acreage, to prove you need to live on the land to look after your animals. If it was that easy, everyone would be doing it, so I suppose thats why its made difficult.
I would speak to the planners, best to have them on side, as once you cross them, life is difficult. A lady not far from us, had a large acreage, and tried to live in a mobile home - seems she had sold her house and barn to other people. It ended that she got an eviction order served, and she could not live in her mobile home within so many miles radius.