the use classes orders made under the Town and Country Planning Act, 1947, followed the example of the Model Clauses made under the 1932 Act in listing a number of “special” industries which were regarded as being sufficiently noxious to warrant special precautions in their siting. These were listed under five use classes, and before land or buildings, whether previously used for other industries or not, could be used for any of these classes, planning permission had to be obtained. A change from one special industrial class to another also needed permission.