Your situation is probably way out of my situation, hope this helps to some degree

I contacted our council for our allotment ( garden at the back of the house ) and was told they hadn't classified them yet so brought them under greenhouse regs 12ft x 10ft max.
The councillor for allotments could not give a proper classification so I guess I could have fought a bigger unit. She did, however, talk me through the regulations and what I could have and what was definitely not allowed. I think each council borough must have their own regs, this may be true for private or agricultural land too, so I would keep on the good side and make contact with the respective councillor. I have found them more helpful if you try to stay within the regulations and sort things out in person or speaking to them.