Androcles link appears to relate to static caravan owners having a pitch on a caravan site. Such caravan site owners will already have planning permission for the running of a caravan site of x pitches. Under that permission, the planning permission permits the owners to occupy the site under set conditions - and one of those is often a limit on the number of months in the year that the owner can reside there.
Your situation is entirely different - you are living on agricultural land with (presumably) no planning permission for a dwelling, temporary or permanant. Hardly surprising, then, that the local authority development control people are showing an interest.
The 'loophole' in the Town & Country Planning Acts that are referring to probably relates to agricultural occupancy. If a worker is engaged in agricultural or forestry work, and a planning application is made for a new dwelling or a temporary dwelling for that worker in the countryside, that application will not normally be denied. The dwelling ends up with an agricultural tie, which means it can only ever be occupied by something in agricultural or forestry work. This part of the law is simply to stop lots of people putting new houses up in the countryside - however it is accepted that houses of agricultural workers need to be near to their work.
To what extent you and your landlord can use that, I am really not sure - how does your boyfriend gain employment in the 9 months of the year he isn't picking fruit? I think the Planning Authority will take a pretty dim of it, if he is working elsewhere than on the land. I have never heard that agricultural occupancy extends to being 'security' on a farm - however it does extend to jobs looking after livestock.