The government guidance that sets out when planning permission is required has been amended following the High Court's decision in Ricki Sage v Secretary of State for Housing, Communities and Local Government & London Borough of Bromley . Paragraph 014 has been removed which previously said:
"Do I need planning permission to home work or run a business from home?
Planning permission will not normally be required to home work or run a business from home, provided that a dwelling house remains a private residence first and business second (or in planning terms, provided that a business does not result in a material change of use of a property so that it is no longer a single dwelling house). A local planning authority is responsible for deciding whether planning permission is required and will determine this on the basis of individual facts. Issues which they may consider include whether home working or a business leads to notable increases in traffic, disturbance to neighbours, abnormal noise or smells or the need for any major structural changes or major renovations."
You can read what the judge, Sir Duncan Ouseley, said about the guidance in the judgment here.
For an overview, you can also read the story about the case here.