The issue to maddress is not whether any residential use is deemed development by it being a change in use, but whether a) the residence could be ancillary to some lawful use or b) a change that does not amount to a material change.

Both require an assesment of fact and degree.

The fact is that there has to be some framework to define a use as residential and secondly whether that residence is sufficient to be material. However even if a change in use is material it still could be ancillary to an otherwise lawful use.

Examples of use that would otherwise be a material change in use requiring planning permission because it is in fact the main use are:-

a) The stationing of equipment or the residence of animals (which clearly includes humans) on land without there being development requires that it is ancillary to the main or combined lawfull uses of the land.

b) the three categories of lawful use are
(i)the existing lawfull use
(ii) agriculture
(iii)foresty.

For instance a horse may be resident in a field for work. Any animal  reared for business or trade or the keeping of an animal as it feeds from the land. Each of these instances the animal is either a major part of the agricultural use of the land as in breeding or feeding or an ancillary use as in working for relatively short period of the year.

A problem occurs when land is used to support animals that are being used for personla or social pleasure.

Likewise the storage of caravans or tractors on land is not a lawful use, useless either it has continued for so long that it is has been established by virtue of time or permission, or there presence is due to their use in  agriculture or forestry.

The logic is that living or animate beings, static or movable equipment can only lawfully occupy land where they are an integral part of an agricultural, foresty or general  land maintenance.

Ther are a number of cases where this has been tested, the few that have come to my attention are
1
2
3
Each of these cases explore whether a change in use is a material change in use and therefore would be classes as development for the purposes of the Act, as a consequence of changes in intensity or  is either a separate and new use of the land or if it is ancillary or part of the existing lawful use or uses.

In 1. The question was: - Is the provision of a caravan, used for workers, in the grounds of a hotel ancillary to the lawful use of the site as a hotel or is it  a separate dwelling that would require its own planning consent.

In 2. The question was:- When is the stationing of caravan, deemed to be a separate use or ancillary. In this case it was considered that a caravan can be used ancillary to agriculture as it's primary function was supporting agriculture, whether as storage for crops, related office work, a temporary shelter for animals or workers or as accommodation for workers managing land.

In 3. The question arose as to the fact and degree of the human residence. It wa acknowledge that the caravan can be use for accomodation where the occupant is mainly employed in lawfull uses, whethe those uses are lawful dueto being outside planning control or existing due to planning permission, but where the degree of accomodation apperars to consistine largley of time and activitils not related to lawfull use then such a use is a separate use and may be considerd a material change is use.

The issue is clearl one onf degree. In three above the appellant failed to show that the intensity of residence was consistent with the quantity of work. The Inspector said that without any substantial evidence is was not shown within reasonable probabilikty that a large part of the residence was not relatede to the  sole lawfull use .