UK: Navigating drop-in permissions post-Hillside

Fifty years and a few months have passed since the High Court’s landmark judgment in Pilkington, which found that where two planning permissions exist in relation to the same land, both permissions cannot be implemented if they are mutually inconsistent.

Pilkington was concerned with a couple of bungalows on a small-holding. Today, though, planning professionals often grapple with how best to reconcile physically incompatible permissions when securing changes to some of the country’s largest and most complex development proposals.

David Wood looks at the latest development in the law and makes the case for a legislative fix.

The background

Pilkington set in train a long and increasingly knotty line of authorities concerned with the compatibility of planning permissions, scheme changes and, most recently, the widely used practice of drop-in permissions.

The Planning Court kicked off 2024 by handing down its decision in R (on the application of Dennis) v Southwark London Borough Council, the latest tangle in the line and the first case to grapple with drop-in permissions in the post-Hillside world.

The Supreme Court held in Hillside Parks Ltd v Snowdonia National Parks Authority that overlapping permissions can coexist where the earlier permission was unequivocally granted as a severable consent.


In Dennis, the planning authority granted a non-material amendment under section 96A of the Town and Country Planning Act 1990 to insert the word “severable” into the description of development of an outline permission for the phased redevelopment of the Aylesbury Estate.

Treating the outline permission as severable would allow the developer to implement a drop-in permission to replace an existing phase of development with a new (otherwise incompatible) form of development.

The claimant argued that on its true construction the outline permission was not, in fact, severable, and that the amendment to make it severable could not be treated as non-material – because its purpose and effect was to make it more flexible, disapplying the Pilkington principle.

The High Court agreed with the claimant and found that the outline permission was not severable before the section 96A amendment.

It was a single planning permission with provisions for phasing. The parties had agreed that, if the outline permission was not already severable, section 96A could not be used to make it so.

The amendment opened up the ability to “mix and match” development by accommodating drop-in permissions, significantly enlarging the “bundle of rights” conferred by the permission.

The amendment was, therefore, material, and went beyond the scope of the powers in section 96A. The purported non-material amendment to the outline permission has been quashed.

On the facts of the case, it is straightforward to see how the High Court arrived at the decision it did. But while the High Court said a lot about the factors that point away from severability – neither phasing alone nor the insertion into a permission of bare terms will be sufficient – it understandably did not make any concrete suggestions as to how severability of a planning permission should be achieved.

What next?

Hillside strategies” necessarily vary from scheme to scheme, and present some real challenges to developers, planners and their advisers alike.

Those formulating consenting strategies need to consider carefully how to future-proof permissions, which need to be made unequivocally severable.

Even so, the treatment of site-wide plans or controlling documents poses real challenges. Those with existing developments involving drop-in permissions need to health-check their consenting strategy with the findings of the High Court in Dennis.

One of the key challenges faced by those promoting drop-in permissions has been to demonstrate to planning authorities the robustness of the structure proposed. Some authorities can be reluctant to engage with the approach given the perceived risks and uncertainty brought about by the recent case law.

The decision in Dennis is unlikely to give those authorities the confidence to embrace the drop-in solution. Yet, for a litany of reasons, the Supreme Court’s proposal in Hillside that developers should simply secure a fresh permission for the entire site surely is not the answer.

Developers, planners and, ultimately, the courts, have had to navigate their way through this uncertainty for half a century. A legislative fix is now long overdue.

There had been a brief window for optimism on this front during the passage through the Lords of the Levelling-up and Regeneration Act 2023, but Lord Lansley’s proposal to allow the Secretary of State to introduce secondary legislation to resolve Hillside conflicts did not make the final cut.

Instead, the 2023 Act left practitioners with the new section 73B of the 1990 Act (applications for permission not substantially different from existing permission), which has yet to come into force and the utility of which remains to be seen.

What form might such a fix take? If we assume that the practice of using drop-in permissions is here to stay, why not start by establishing that outline planning permissions are deemed to be severable, allowing defined phases to be taken out and replacement development slotted in?

This would require developers and authorities to engage in the judicious use of conditions and planning obligations to ensure that amended developments continue to be coherent, integrated proposals that work as a whole.

Scheme changes will need to be explained with clarity and transparency, and subject to full consultation and environmental impact assessment to ensure public confidence in and understanding of the system. That said, those engaging in best practice are doing all this already.

Scheme changes and drop-in permissions give rise to considerable uncertainty and planning risk.  Navigating that risk is a poor use of the resources of planners, developers and the courts. It is time for legislation to step in.

An earlier version of this article appeared in EG on 13 February 2024.


Authored by David Wood.


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