The legal definition of agriculture is as follows:
"Section 336 of the Town and Country Planning Act 1990 defines ‘agriculture' as including:
‘horticulture, fruit growing, seed growing, dairy farming;
the breeding and keeping of livestock (including any creature kept for the production of food, wool, skins or fur, or for the purpose of its use in the farming of land);
the use of land as grazing land, meadow land, osier land, market gardens or nursery grounds; and
the use of land for woodlands where that use is ancillary to the farming of land for other agricultural purposes.’"
It technically doesn't matter if this is for personal use or a business, if this is how the land is used and there is an income (even self sufficiency) it is classed as agricultural, although some councils will create grey areas and deny this.
Someone mentioned Chapter 7, I rang them last year about a similar issue, but on a much smaller scale, and they were very helpful, but I think they were stopping the helpline.
There used to be a rule that certain livestock kept on a plot more than 6 acres helps to get planning permission, even if it's temporary, under the caravan act, and it may be easier to get planning for a log cabin whose dimensions come under the caravan act, so that might be worth looking into. IIRC pigs and alpacas were among the livestock that can help, as you need to be on site more. This might have changed though.
Hiring a land barrister (may be a different wording, but basically a barrister who knows the laws surrounding planning and agriculture inside out) can be helpful, as any council created issues (which they are VERY good at doing!) can be overturned immediately. It can be costly, but cheaper in the long run.