The proposed use of any premises - freehold or leasehold- must be authorised under planning legislation. Where there is to be a change of use, planning permission must be obtained. However an application for planning permission does not need to be submitted where the change is within a category or 'class' of the Town and Country Planning (Use Classes) Order 1987. These classes are often adopted in practice and B1 includes, for example, uses as offices which are not primarily open to visiting members of the public.