In the first of a new series of quick answers to planning problems, we look at stretching a planning permission
Having obtained planning permission for a development, can the developer amend it in any way? Some planning authorities will agree minor modifications to developments, some will not. What are the legal principles?
The legal testThe classic test for the validity of an amendment to a planning application is "the result must not be substantially different from the development applied for". It is for the planning authority to exercise reasonable judgment as to whether there is a significant difference or not.
Enlargement of the site between lodging an appeal and its determination, will not automatically make the change invalid, but it has to be treated with special care. Whether the amendment had been subject to public comment is relevant.
Those planning authorities who refuse to allow minor amendments refer to the Sage case (Sage v Secretary of State for the Environment, Transport and the Regions  UKHL 22). However, that was a planning enforcement case and whether a minor amendment was involved was not in issue. The correct current test is as set out above.
These principles raise the potential for planning permissions to be “stretched”. For example, outline planning permission is granted for development of a certain size, for example, by reference to floorspace or numbers of dwellings. It may be possible to obtain reserved matters approval which exceeds such limits if the change is not “significant” or “substantial”. Another example is where an outline permission sets parameter blocks for development, and the details fall within those blocks. Environmental assessment can cause problems where the likely significant environmental effects would change due to the stretching of the permission.
Possible legislative changesThe planning legislation does not allow for minor amendments or "stretching". However, one of the changes in the Planning Bill will allow a person interested in a development site to apply to the planning authority for it to make a change to any planning permission for that site it is if satisfied that the change is “not material”. In deciding whether a change is “material”, the planning authority must have regard to the effect of the change, together with any previous changes it has made, on the planning permission.
The existence of a clear statutory power for minor modifications will be welcome. There may be the possibility for disputes and the spectre of judicial review hanging over the question of whether any given change is "material". Existing case law will still be relevant.
Tim Ayres is senior associate at Pinsent Masons