Excavating new basements may rarely be an issue outside of London (Edinburgh restricts itself to conversion of cellars), but the recent English High Court decision in Eatherley v London Borough of Camden shows the complexities of applying the definition of “development”.

The judge held that development of a new basement, when there is nothing underneath at present, could involve two activities:

  • enlargement, improvement and alteration
  • also an engineering aspect of excavating a space and supporting the house and its neighbours

As a result, the planning authority should have assessed the additional planning impacts of the engineering works to decide whether they amounted to a separate activity of substance.