What do Pilkington and Hillside Mean for "Drop-In Applications"?

What is Pilkington?

The Pilkington principle, arising from Pilkington v Secretary of State for the Environment (1973), states that a planning permission becomes void if implementing it renders other existing permissions on the same site unachievable. It emphasises that development must remain consistent with earlier permissions unless revoked or varied.

What does Hillside have to do with Pilkington?

The Hillside judgement (Hillside Parks Ltd v Snowdonia National Park Authority, 2022) reaffirms Pilkington while addressing inconsistencies in planning permissions for multi-phase developments. It clarifies that implementing a materially inconsistent permission nullifies prior permissions for the same site. For example, if Permission B physically conflicts with and is implemented after Permission A, then completing Permission A becomes legally and practically impossible.

What are 'drop-in applications'?

The judgement has critical implications for "drop-in" applications, a practice where developers seek to modify parts of larger schemes without affecting the whole. Hillside highlights that such strategies are risky unless permissions are clearly severable and require careful legal drafting to ensure that inconsistencies do not arise. This is particularly evident in cases where courts may demand a fresh, unified application covering the entire site, adding cost and complexity.

What are the implications of Hillside for future planning permissions?

Crucially, Hillside introduced practical clarity by confirming that prior works under a valid permission (e.g., Permission A) remain lawful even if further development is stopped due to incompatibility. This safeguards developers from enforcement action for work lawfully carried out.

Hillside reinforces the need for cohesive planning strategies, discouraging piecemeal development and emphasising the importance of careful, proactive planning, especially in complex, phased developments.

Caution is required when using 'drop-in' applications