Hillside Revisited 4: Physical differences must be material?

United KingdomScotland

1. Introduction

This is the fourth Law-Now in a series on the Supreme Court’s judgment in Hillside Parks Ltd v Snowdonia National Park Authority. The first Law-Now is available here, the second here and the third here.

In Hillside,[1] the Supreme Court confirmed and to some extent clarified how to approach overlapping planning permissions.

2. The Supreme Court Judgment in Hillside

A key point from the judgment in Hillside, is the Supreme Court’s analysis on the use of overlapping/inconsistent planning permissions on the same piece of land – known as “the Pilkington principle”.

Pilkington considers the consequences of multiple planning permissions being implemented on the same site. For example “Permission A” and then “Permission B”, where Permission B has been implemented and developed and Permission A has not been implemented (or has been implemented but has not been completed).

The Supreme Court concluded in Hillside that development rights under Permission A cease to be available if it is “physically impossible” to develop under Permission A because of the Permission B development.

Helpfully, the Court emphasised that the Pilkington principle should not be interpreted too rigidly. Some non-material physical differences between the developments under Permissions A and B will not be enough to make reliance on Permission A unlawful. The Court noted that it would be unrealistic for all future development pursuant to a planning permission to be unlawful unless there is “exact compliance” with the planning permission in large multi-unit developments.[2]

The Court suggested that the physical differences between Permissions A and B would only be fatal to Permission A if they are material in the context of the scheme as a whole. This is the “ordinary presumption” which must now be applied, although what is or is not material is a matter of fact and degree that will depend on the circumstances of each case.[3]

The Court drew an analogy with s96A Town and Country Planning Act 1990 which authorises non-material amendments to planning permissions. It can be inferred from the judgment that if a physical difference between the developments is something that could ordinarily be consented as a change to Permission A, then this will not render development pursuant to Permission A unlawful

This means that if there is a small difference between the way the proposed development aligns with the highway, or a minor difference in the orientation of the building then development may continue pursuant to Permission A. However, caution must be exercised because the effects of a change must be considered when deciding whether it is non-material. For example, if a small change to the orientation of a building has a significant impact on the privacy of residents on adjoining land then this may be too material. In this case the change could render it impossible to continue with development under Permission A.

Hillside also provides authority that a mere inconsistency between the conditions attached to two planning permissions does not mean that the developer must necessarily choose between them in terms of which to rely on for future development. Please refer to our earlier Law-Now for further explanation of this aspect of the judgment.

3. Conclusion

The Supreme Court’s judgment in Hillside approves the longstanding Pilkington approach whilst couching it in clear terms (“physical impossibility”) and providing the useful, common-sense clarification that physical differences which are not material will not be automatically fatal.

The piding line between “material” and “non-material” physical differences will need to be carefully considered on a case-by-case basis and whilst bearing in mind the whole context of the development. The risk of falling fouling of Pilkington is the potential loss of valuable development rights.


[1] Hillside Parks Ltd v Snowdonia National Park Authority [2022] UKSC 30.

[2] Hillside, [69].

[3] Hillside, [69].