Live/work units, if they are such that they provide the opportunity for living and working within a single self-contained unit and neither the residential nor the business use is ancillary to the other, would be classified as a sui generis use in the context of the Town and Country Planning (Use Classes Order) 1987, as amended.
Where a single dwelling is used for both living and working, but the primary use remains as a dwelling and the business use is ancillary, this use would fall within the “C3: Dwelling Houses” class of the Town and Country Planning (Use Classes Order) 1987, as amended.
It is for local planning authorities to determine, taking into account individual characteristics, as to which class or otherwise a particular premises belongs.