What are Caravans?
Caravan refers to any building that’s designed to be lived in and can be transported by road. The term ‘caravan’ covers traditional touring caravans, static caravans and mobile homes.
Touring caravans, motor homes and caravan holiday homes and collectively know as Leisure Accommodation Vehicles (LAV). Twin-size mobile homes are referred to as Residential Park Homes (RPH).
Touring Caravans: These are the ones we see towed behind cars. Designed for occasional recreational use. They are built to BS EN 1645 and must meet the requirements for the construction and use of road vehicles.
Motor-caravans incorporate the living accommodation similar to that of a touring caravan onto a motor base vehicle and are therefore designed specifically for touring. They are built to BS EN 1646 and must be road legal.
Static caravans, also called holiday caravans and single units, are designed for recreational use not yearlong residential use. They are not directly towed on road but transported in one complete section on a HGV trailer. They are built to BS EN 1647.
Mobile homes, known as twin-unit caravans, are assembled from two sections. They are not designed to be directly towed on road by a vehicle but must remain transportable in one section and two separate sections. Mobile Homes designed for residential use are often referred to as Park Homes, which are built to BS 3632.
Other Vehicles such as motorised caravans or converted coaches can also be caravans but any form of tent is not.
Notes on; Case Law.
Refer to the actual documents in all cases. This is not legal advice.
Brightlingsea Haven Limited and another v. Morris and others 2008 EWHC 1928 (QB)
On conforming to the mobility test. Site Access…
‘The two opposing constructions are these: whether the structure must be capable of being moved by road from one place to another, with no specific places or roads in mind, or whether the structure must be capable of being moved from where it is and moved by road to another place. I have concluded that the first construction is the correct one. My main reason is that it is consistent with the purpose of the Act that, if a structure is once a caravan, it should remain a caravan if it is itself unaltered, regardless of where it is. If a lodge meeting the requirements of the section and so a caravan is assembled on a site, it should not cease to be a caravan if it becomes boxed in by other lodges and cannot be got out because lifting apparatus cannot sufficiently approach… In my judgment the test which the structure has to pass is as follows. It must either be physically capable of being towed on a road, or of being carried on a road, not momentarily but enough to say that it is taken from one place to another. It is irrelevant to the test where the structure actually is, and whether it may have difficulty in reaching a road’.
Carter and Another -v- Secretary of State for the Environment and the Carrick District Council 
1 WLR 1212
This case law gives clarity to the mobility test, twin-units must be movable when assembled as a whole.
In this case The Secretary of State has taken the view that, to satisfy the definition ‘a structure must be capable of being moved as a structure (that is, in one piece)...’ This view was upheld by the Court of Appeal. The reasoning appears perhaps most clearly from the judgment of Russell LJ
"In order to qualify for the description 'caravan' in section 29 it is therefore 'the structure' that has to possess two qualities. The first part of the section provides that it is necessary for 'the structure' to be designed or adapted for human habitation. This, in my view, clearly contemplates the structure as a whole, as a single unit, and not the component parts of it. The second quality which 'the structure' has to possess is mobility. The structure has to be capable of being moved by being towed or transported on a single motor vehicle or trailer. 'The structure' contemplated by the second part of the section is, in my judgment, precisely the same structure as that contemplated by the first part of the section, not a structure which has been dismantled before loading has taken place. In my view the second limb of the definition can therefore refer only to a whole single structure and not to component parts of it."