Hillside Parks Ltd v Snowdonia National Park Authority

A planning permission for a large development will generally be construed holistically. Unless its true construction reveals separate and independent acts of development, material departure from the approved scheme means that the permission cannot lawfully authorise the remaining development. The exception for severable acts is narrow. Minor deviations do not necessarily invalidate a complex development, but physical impossibility of completing a material part of the approved scheme does. A declaration that development may be completed in the future does not guarantee that result against later physical changes or changes in law. Where subsequent development makes completion of the original scheme physically impossible, further development requires fresh planning permission.

Hillside owned land subject to a 1967 planning permission for a 401-dwelling housing estate. In 1987 Drake J declared that the permission had been implemented and that the permitted development could lawfully be completed in the future. Subsequent development was carried out under further planning permissions, materially altering parts of the approved layout.

Hillside sought declarations that the 1967 permission remained valid and capable of completion, and that the Authority was bound by the 1987 Order. The Authority contended that the original scheme was holistic and that later development made its completion physically impossible. The central questions were whether the 1987 decision was legally wrong and whether later events prevented reliance on the declaration.

1. The claim was dismissed. The court held that the 1967 permission authorised a coherent housing-estate scheme, not a collection of freely severable development acts. Its references to clusters of dwellings did not alter that construction. The F. Lucas & Sons Ltd v Dorking and Horley Rural District Council exception therefore did not apply.
2. Planning permissions must generally be construed holistically. Development under a single permission must be carried out fully in accordance with it. Physical impossibility of implementing or completing a material part of the approved scheme renders the remaining development unlawful under that permission. The principle should be applied with practical common sense: immaterial deviations in a large and complex scheme do not automatically invalidate the whole development.
3. Development carried out under later permissions remains lawful by virtue of those permissions. However, where it is materially inconsistent with the original permission, the totality of the development cannot ordinarily be completed wholly in accordance with the original scheme.
4. The court was not satisfied that Drake J had been wrong in 1987. On the limited evidence, the earlier additional permissions could properly have been construed as authorising modifications to the original permission. The backward-looking challenge to the 1987 Order therefore failed.
5. The 1987 declaration was prospective only in the relevant circumstances. It did not determine that completion would remain possible despite later physical alterations or changes in law. By 2019, development in the north-west part of the Site made completion of the original scheme physically impossible. The remaining development required new design and fresh planning permission.
6. The question whether the Authority was bound by the 1987 Order regardless of legal error did not need to be decided.