In the 2022 case of Hillside Parks Ltd v Snowdonia National Park Authority, the Supreme Court considered the effect of successive and mutually inconsistent planning permissions granted for development of the same site. It held that development carried out under a ‘drop-in’ permission, which makes the development under the earlier permission ‘physically impossible’ to complete, will render unlawful further development under the earlier permission.

What is a ‘drop-in’ permission?

A consented development can be varied by applying for either a non-material or a minor material amendment under the Town and Country Planning Act 1990. There can be legal and practical difficulties with these options, which has led to the use of so-called ‘drop-in’ permissions. 

A drop-in permission is granted following a standalone planning application to alter a discrete part of a wider development that has already been approved under an earlier permission. This option was previously attractive to developers, as it appeared to allow a small area of a wider development to be altered more easily without requiring updated reports to be prepared in relation to the site as a whole. Drop-in permissions appeared to provide a level of flexibility for developers, especially on larger schemes which will be built-out over several years.

How did the Hillside case come about?

Planning permission for a site in Snowdonia National Park was granted for the development of 401 homes in 1967.

The 1967 permission was partially implemented with 41 houses being built. However, between 1996 and 2011 several drop-in permissions were granted, a number of which were described as varying the 1967 permission. Concerned with the way the site was being developed, the park authority obtained advice that the implementation of successive, inconsistent permissions meant it was no longer physically possible to continue development under the 1967 permission. Hillside Parks Limited was therefore told to stop carrying out development.

The developer turned to the courts, seeking confirmation that the 1967 permission remained valid and the development could be completed. Both the High Court and the Court of Appeal found that the 1967 permission could not be lawfully completed because the subsequent drop-in permissions were inconsistent with it.

What did the Supreme Court say?

The Supreme Court dismissed Hillside’s appeal, although it did distinguish between physical impossibility and ‘mere incompatibility’ - a later drop-in permission that is merely incompatible with an earlier permission will not render unlawful further development under the earlier permission.

Why is this judgment so important?

For developers, deciding whether implementing a later permission is physically impossible or merely incompatible with earlier development may be an impossible task. While this part of the judgment leaves some very much reduced scope for drop-in permissions, establishing the effect of a subsequent proposal on an existing permission will in each case be a question of fact and degree.

Developers and their lenders will need to stay alert to the risks of implementing successive, overlapping planning permissions, particularly in relation to larger schemes involving multiple developers.

This article is for general information only and reflects the position at the date of publication. It does not constitute legal advice.