Current English Heritage guidance states that the boundary of a conservation area should be identified through appraisal and following guidance. Consideration should be given to whether the immediate setting also requires additional controls that result from designation, or whether the setting is itself sufficiently protected by national policy or the polices in the development plan. This would also be a consideration when deciding whether to include a historic park and garden, and by extension, historic commons and greens.
English Heritage guidance also now recognised that the boundaries of some conservation areas may have been drawn too tightly. For example the full extent of historic rear plots, which are often of archaeological interest and an essential part of the framework of an historic town, were omitted, or the Victorian or Edwardian phases of development, parks, cemeteries and historic green spaces now considered of special interest, were excluded. In such cases the existing boundary may need to be extended.