It is common for developers to submit applications to vary planning permissions in response to changes in social, environmental, market and economic factors. In some cases, what a developer wants to build no longer falls within the parameters of the original planning permission. Sometimes the changes required are so significant that they exceed the limits of section 73 applications (often called minor material amendments) and section 96A applications (often called non-material amendments).
Until recently in this kind of scenario a developer may have considered making a "slot-in" application (sometimes also called a drop-in application): that is to say a standalone planning application that overlaps and slots into a phase or part of an existing consented planning scheme with the intent that the new "slot in" permission will be built out alongside the remainder of the original wider planning consent. Typically, a slot in will relate to a distinct phase, and the intention will be to develop the rest of the planning scheme under the original consent.
However, as a result of the Supreme Court judgment in the case of Hillside Parks v Snowdonia National Park Authority [2022] UKSC 30 "slot-in" applications should be treated with extreme caution due to the risk of "slot-in" permissions (if implemented) potentially making it unlawful to carry out further development under pre-existing planning consents.
Following on from the Hillside Judgment, the High Court has recently handed down judgment in the case of R (on the application of Aysen Dennis) v London Borough of Southwark [2024] EWHC 57 (Admin) which highlights why developers and local authorities should continue to approach this issue with caution.
We consider each of the judgments in turn and summarise the implications for those contemplating seeking changes to existing planning schemes:
Hillside
In the case of Hillside a full detailed planning permission was granted in 1967 for the development of 401 dwellings in Snowdonia National Park with a detailed masterplan drawing, showing the location of each dwelling and the layout of the roads for the estate. Between 1996 and 2011 six planning permissions were granted for dwellings departing from the 1967 masterplan, which were built and occupied.
The question for the Supreme Court was whether, in light of these subsequent permissions, the 1967 permission was still valid. In consideration of this question, the Court upheld the Pilkington principle (Pilkington v Secretary of State for the Environment [1973] 1WLR 1527), which held that where development is carried out pursuant to a subsequent planning permission which makes it physically impossible to carry out development pursuant to an earlier permission, then the earlier permission can no longer be relied upon in respect of development that has not yet been carried out. The Hillside decision explored a concept of "severability": the idea that a planning permission could be expressed in such terms so as to allow a developer to build out part of a site under planning permission A (i.e. the original permission), whilst building out other parts under planning permission B (i.e. a slot in permission). This would only be possible if permission A could be interpreted to have granted consent for development that has severable parts so that implementing a different permission on a severable part did not prejudice the original planning permission. Unfortunately, the Supreme Court did not say what the test for "severability" is, and this is therefore something that is subject to uncertainty. For example, in the context of a phased permission, should each phase be construed as a severable part of the original permission?
Dennis v LB Southwark
In the case of R (on the application of Aysen Dennis) v London Borough of Southwark [2024] EWHC 57, the London Borough of Southwark (LBS) granted an outline planning permission (the OPP) in 2015 for part of the Aylesbury Estate to be delivered in three phases. Part of the first phase (phase 2A) of the OPP was built out by Notting Hill Genesis (NHG) between 2020 and 2023.
NHG then submitted, in 2022, a 'slot-in' application for detailed planning permission for phase 2B to deliver a greater number of new homes, in line with changes to the development plan policies (the Slot-In Application). The officer report in respect of the Slot-In Application considered that, if granted and built out, would not prevent the remaining phases of the OPP being built out as the situation was different to Hillside in that the OPP was a phased permission in outline.
Following a resolution to grant the Slot-in Application, NHG submitted an application under section 96A of the Town and Country Planning Act 1990 to make a non-material amendment to vary the description of the OPP to state that it was a "…severable phased permission…". The section 96A application was subsequently granted.
The claimant challenged LBS' approval and argued that this amendment was in fact "material" (falling outside of the auspices of section 96A) in that "the purpose and effect of the amendment is to change the bundle of rights granted by the OPP".
It was common ground between the parties that if the OPP was not already "severable", then the amendment was material and therefore the grant of the amendment under section 96A was unlawful. The case therefore turned on whether a planning permission that was expressed as a phased permission could be interpreted as being a planning permission whereby each phase was a severable part of the permission. The Court held that "the mere fact that development is to be implemented in phases (following approval of reserved matters) does not alter the effect of the Pilkington principle where an inability to satisfy the physical impossibility test cannot be circumvented. In this regard there is no material difference as a matter of principle between detailed and outline permissions."
The High Court considered the OPP in some detail, noting parts of the planning statement, design and access statement, design code strategy and parameter plans as well as conditions. The Court noted the application documents which appeared to show the intention to deliver comprehensive regeneration of the Estate. The Court considered that the phasing plan, and sequence of delivery of the phases set out in the design and access statement were inconsistent with a servable planning permission. The Court held, looking at the OPP and the submissions as a whole, that there was "no contra-indication, let alone a clear indication, that the OPP was severable".
The court ultimately ruled in favour of the claimant and concluded that the OPP was not severable prior to the grant of the S96A consent, and as such the amendment was a material amendment. The grant of the s96A consent was therefore unlawful and quashed.
Government to legislate?
The Government is currently consulting on the implementation of the new S73B of the Town and Country Planning Act 1990 (as inserted by the Levelling Up and Regeneration Act 2023). The new S73B consenting route is intended to make it easier to achieve changes to existing consents, and would extend to changes to the description of development and to conditions, provided that the effect of the change will not be "substantially different" from that of the existing permission. This could potentially avoid the need for slot in applications in some cases. But the Government has also noted in the consultation material that slot in applications may still be necessary. The Government is looking at how the issues highlighted in Hillside could be legislated for to enable consents to sit side by side in appropriate cases.
Impact
The key lessons from both Hillside and Dennis are as follows:
- Avoid submitting slot-in applications where an existing consent is deemed not fit for purpose for a particular phase, unless you are content that the remainder of the existing consent no longer needs to be relied upon or you have received legal advice that the existing consent is 'severable' and that the slot-in will not make it physically impossible to carry out later phases of the existing consent;
- if you are looking to acquire a site where the planning consent you intend to rely on may have been affected by slot-in permissions, obtain a legal opinion before proceeding;
- when buying land that forms part of a wider planning scheme that has not been fully built out, make sure you obtain appropriate contractual protections from the owners of the wider planning scheme that they will not implement any slot-in permissions that could prejudice the planning consent that you intend to rely on;
- when selling land that forms part of a wider planning scheme that has not been fully built out, if you are retaining land for future development make sure you obtain appropriate contractual protections from buyers that they will not implement any slot-in permissions that could prejudice the planning consent that you intend to rely on in respect of the retained land; and
- when submitting new planning applications, carefully consider how the application documents, description of development and planning conditions can be drafted so as to make it clear that the resulting permission will be a permission of severable parts, i.e. individual acts of development and ensure that planning policies are assessed against each act and justified in planning terms and undertake a legal review before submitting the application. However, even with careful drafting it remains unclear in law what is required to create "severable parts" and therefore caution is advised.
- Watch this space – will the Government introduce legislation to deal with the issues arising from Hillside?
