Prior to 1998 there was some debate in the cases as to whether mobile homes were or were not buildings with regards to planning. The factors of permanence and attachment are the relevance considerations.
This issue was settled in 1998 in the case of Measor v. Secretary of State for the Environment, Transport and the Regions. The case was heard in the Queen's Bench Division of the High Court and is therefore binding on planning inspectors. In it the Judge stated:
"In my judgment, it would conflict with the purpose of the Act and common sense to treat mobile caravans as "buildings" as of right. While I would be wary of holding that, as a matter of law, a "structure" that satisfied the definition of, for example, a Mobile home under s.13(1) of the 1968 Act could never be a building for the purpose of the [Town and Country Planning] Act 1990, it seems to me that Éby reference to the definitions in the [Caravan Site and Control of Development] Act1960 and the 1968 [Caravan Sites]Act it is clear that in the present case the caravans lacked that degree of permanence and attachment to constitute buildings"
Despite the Courts being anxious not to state that a caravan or mobile home could never be a "building", generally they are not. The Measor principle has been restated and approved in a number of cases since 1998.
As recently as 19th June 2002 Mr Justice Forbes in the case of Massingham v Secretary of State for Local Government and the Regions stated at paragraphs 15 and 19,
" The judgment in the Measor case restated the approach to the definition of a building for the purposes of development control which had been well settled in previous cases including Barvis Limited v Seceretary of State  In acknowledging that it would be wrong to say that a mobile home could never be a building. In this case I am in no doubt that the mobile home fails the tests of permanence and attachment established by the courts"
" I can see no basis upon which it can be said that the Inspector fell into error when reaching his conclusion to the effect that what had happened on the site constituted neither operational development nor development consisting of a change of use from a caravan to a permanent dwellinghouse"
In the Massingham case, the mobile home in question was being used as a second home and was supported by concrete slabs. Despite the fact that the wheels of the home remained on the caravan, the axles were supported on blocks, and as Forbes J. pointed out elsewhere in the judgment the connection to mains services is not relevant in determining whether a caravan is a building.