Hillside not a landslide: Getting development done post Hillside and Dennis judgements

What matters

What matters next

Following the recent High Court decision in R (Dennis) v LB Southwark [2024] EWHC 57 (Admin), Shoosmiths’ planning practice has received a raft of queries over the issue of ‘drop in’ consents, and the future-proofing of planning permissions for large multi-phased developments.

There has been much debate on the issue.

The purpose of this analysis is to cut through that noise and provide practical guidance on:

  • Setting up a planning permission from the outset to maintain maximum flexibility, without falling foul of the issues that arose in the Hillside and Dennis cases
  • The scope to alter the approved development once planning permission has been obtained

The analysis seeks to focus on ways to ensure that the decisions reached in both cases do not become further barriers to development, in a market and political environment that is already difficult.


Pilkington v Secretary of State for the Environment [1973]

This case established the principle that where two or more planning permissions have been granted on the same area of land and development has been carried out under one of those permissions, if that development has made it physically impossible to carry out development approved by another consent, then that may no longer be relied upon = commonly referred to as the ‘Pilkington Principle’.

The rationale behind the decision was that the Court wanted to avoid the risk of development taking place selectively under a mixture of planning permissions, where the impact of the combination of development has not been assessed as a whole and where it is physically impossible to carry out the remainder of the consent.

Hillside Parks Ltd v Snowdonia National Park Authority [2022]

The judgement in the Hillside case clarified the Pilkington Principle.

In the Hillside case, planning permission had been granted in 1967 for an estate of 401 dwellings. The planning permission was accompanied by a master plan, which specified the location of each house and the layout of the roads serving the development. However, of the 41 houses that had actually been built on the site, none of them reflected the requirements of the master plan, as the developers had instead relied on a series of separate planning applications to develop the site out.

In 2017, the Snowdonia National Park Authority informed the owners of the site, Hillside Parks Limited, that it could no longer continue to build out in accordance with the 1967 permission.

This prompted Hillside to take High Court proceedings, seeking a Declaration that the 1967 permission remained valid and could be carried out to completion, as set out in a previous High Court Declaration obtained in 1987. This had stated that the 1967 permission could still be lawfully completed in accordance with the master plan “at any time in the future”.

The case went all the way to the Supreme Court, which ruled in the National Park’s favour and reached the several conclusions.

Firstly, it applied the Pilkington Principle, concluding that because of the multiple separate consents obtained on the site, it was no longer possible to continue building out under the 1967 permission, and therefore no further lawful development could take place pursuant to the 1967 consent.

The Court also made it clear that the starting point for interpreting a planning permission for a multi-unit development is that the consent is for the development as a whole, and does not authorise a set of permissions to construct each individual element of the scheme. However, a planning permission can be constructed to be deliverable in separate elements if the application is prepared and assessed on this basis, and the permission is expressly stated to be severable.

Finally, the Court fully endorsed the Pilkington Principle, but then added that the principle should not be taken too far. The Court made it clear that the benefit of a planning permission will not be lost if there are minor, rather than material departures from it, and this is particularly relevant when considering changes to large multi-unit developments.

R (Dennis) v LB Southwark [2024]

This case related to introducing the word ‘severable’ into the description of development on an outline permission via the use of a Section 96A non-material amendment application.

The High Court determined that if a planning permission is not severable in the first place, then it is not made severable simply by seeking to amend it by inserting the word ‘severable’ in the description of development. Therefore, the applicants needed to show that the outline permission was severable in the first instance as a matter of fact.

The Court examined whether there was evidence that the original outline was in fact intended to be severable, and whether the merits of the original scheme had been assessed on this basis.

The Court concluded that it had not.

In reaching this decision, the Court looked at the several aspects of the original application.

On the approach to phasing, the Court concluded that phasing provisions were not sufficient evidence of a severable permission. Phasing is common on large outline schemes, with different component parts and that is not inconsistent with a single permission. The design and access statement required phasing to come forward in a particular way, evidencing that the outline permission was not severable.

The parameter plans and physically discrete nature of the phases were also not inconsistent with a single permission.

Different phases were granted with separate time limits for implementation. Again, the Court held that this was not inconsistent with a single planning permission, and this does not mean that it can be disaggregated.

Making a consent severable to allow for changes to the scheme at a later stage

The Hillside and Dennis cases turned on their own facts and the conclusions should not be interpreted to mean that applicants are “stuck” with consents as they were originally granted.

It is still possible to maximise the flexibility of a consent by considering the following factors.

From the outset, planning and technical teams should be instructed that flexibility is needed in how the development is to come forward. The team then needs to draft the Planning Statement, Environmental Statement and all other supporting documents on the basis of this approach. For example, it needs to be clear in all the documents that each discrete element of the development has been assessed on its own merits, as well as the development as a whole having been assessed.

The crucial element here will be to work out how to break down each element of the proposed development for this piece by piece assessment. The parts of the development being assessed may need to be smaller than usual phased development parcels, especially if an organisation wants to maximise the ability to tweak the scheme over time.

The aim is to build up an evidence trail from the outset that each jigsaw piece of the development has been assessed. This involves two things – firstly, fixing the parameters of the proposed development that will take place on each jigsaw piece (scale, height, massing etc.); and then clearly showing how the impact of the proposed development (up to those parameters) has been assessed both as a free-standing jigsaw piece, but also how all the pieces fit together as a whole and have been assessed, and found to be acceptable in planning terms. Retaining an assessment of the impact of the development as a whole is important is important to avoid any risk of the EIA falling foul of the rules against “salami slicing” of assessments.

The importance of this is that, once each jigsaw piece has been assessed and deemed acceptable by the local planning authority (LPA) then, as long as the organisation stays within those parameters, there should be less of a problem with modifying parts of the development - either by applying for new reserved matters approvals or through obtaining new “drop in” detailed approvals.

Once this evidence base has been built up in the planning application document, the position can be strengthened further by using a description of development that makes it clear that the development is intended to come forward as a multi-phase, severable development scheme.

This approach then needs to be followed through by the LPA in the Committee Report.

In Dennis, there was no evidence in the approach taken in the officer’s report and nothing in the environmental statement that supported the position that component phases could come forward separately.

What is needed is an evaluation in the Committee Report that each “jigsaw” piece has been considered against the development plan and that each element of the scheme has been assessed on its own merits, as well as part of the wider assessment of the overall development scheme.

The final thread is consideration of how the planning conditions, and any Section 106 agreement are to be drafted to ensure that the requirements of the conditions and agreement can be complied with on a phased, or even sub-phased basis.

Amending an existing consent

Even if it does not say on the face of a planning permission that it is severable, the case of Hillside does not completely prevent any drop-in permissions from being utilised, but the drop-in permission must not make it physically impossible to carry out the development approved by the original consent, otherwise the original consent cannot lawfully be continued. If the difference between one planning permission and a later one is not material, the earlier one may still be capable of implementation.

It is possible to minimise the risk of a drop-in application creating a Hillside issue by:

  • Ensuing that the new application accords with the Pilkington Principle, i.e. ensuring the delivery of the new element of development does not render the rest of the original consent physically incapable of being built out.
  • The drop-in application needs to integrate into the overall scheme, without compromising the ability to deliver the remainder of the originally consented scheme.
  • Ensuring that the new element of development - when added to the original consented development - does not take the scheme as a whole beyond the assessed parameters of the original consent.
  • Ensuing the quantum and type of development is not materially different to that authorised under the original consent.
  • Minimising any amendments to key infrastructure serving the development, for example access routes, as changes to these are generally more likely to give rise to Hillside issues - they could well constitute a material change to the approved development, taking the proposed changes outside of the parameters of the original consent.
  • Considering the use of Section 96A and 73 applications to update the phasing of the overall development to illustrate how the drop-in application fits in with the rest of the scheme, and would not act as a physical barrier to the rest of the development site being built out.


This information is for general information purposes only and does not constitute legal advice. It is recommended that specific professional advice is sought before acting on any of the information given. Please contact us for specific advice on your circumstances. © Shoosmiths LLP 2024.



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