Many of us would like more space in our homes, increasingly homeowners are doing this by converting their cellar to create a basement storey. Unlike loft space which lends itself best to creating additional bedrooms, a basement has a much more flexible range of uses, everything from additional family living space to a utility room. In addition basements can be converted with their own external entrance to create a self-contained unit. Converting an existing cellar from a storage area to habitable space involves only a change of use and does not require planning permission. However excavating the floor of a cellar to improve the ceiling height is treated as an extension and so may need planning permission. Modest extensions and alterations can be undertaken without a planning application under Permitted Development rights. In any case you should contact the local authority before planning any works.