Inconsistent permissions and the Pilkington principle

Holding two planning permissions over the same land is common and perfectly lawful. What is not always possible is implementing both. Where development carried out under one permission makes it physically impossible to build out the other in accordance with its approved plans, the second permission cannot be implemented. That is the Pilkington principle, taken from the 1973 case of the same name, and the Supreme Court restated it in Hillside Parks Ltd v Snowdonia National Park Authority in 2022.

The practical danger is not holding the permissions. It is starting work under one of them without working out what it does to the other.

Holding more than one permission on a site

A planning permission attaches to the land and, once granted, cannot be abandoned by the person who obtained it. That principle, settled in Pioneer Aggregates, means an unwanted permission does not evaporate because the owner changed their mind.

So sites accumulate permissions. An outline consent from 2015, a full permission from 2019, a section 73 variation from 2022 and a drop-in application for one phase can all sit live at once. Each section 73 permission is a new and independent permission that exists alongside the original rather than replacing it, which is why the file grows.

None of that is a problem in itself. The problem arrives when someone assumes that holding a permission means it can still be used.

Why implementing one can kill another

Pilkington concerned a smallholding where permission had been granted for a bungalow on one part of the land, and that bungalow was built. A second, earlier permission authorised a bungalow on a different part of the same holding, on plans that showed the remainder of the land undeveloped.

The court held that the second permission could no longer be implemented. Building the first bungalow meant the development authorised by the second permission, read with its approved plans, could not be carried out. The land was no longer in the state the second permission assumed.

Hillside applied the same reasoning to a large multi-phase residential scheme where successive later permissions had been granted and partly built. The Supreme Court held that where a later permission is materially inconsistent with an earlier one for a single scheme, continuing to build out the earlier permission may become unlawful, and that a permission for a multi-unit development is not normally severable into separately implementable parts.

The test the courts apply

The question is framed by reference to the permission you want to use, not the one already implemented.

Look at what that permission authorises, including its approved plans and conditions, and ask whether it is still physically possible to carry out that development in accordance with them, given everything that has been done on the land. If the answer is no, the permission is incapable of implementation, whatever anyone intended.

Two points follow that catch people out. Intention is irrelevant. And it is a question of physical possibility rather than of planning merit, so the fact that a council would happily grant the scheme again does not revive a permission that can no longer be carried out.

Partial implementation makes the analysis harder rather than easier. Works that have begun but not completed still change the state of the land, and an assessment has to be made on the facts as they stand.

Overlapping red lines and drop-in permissions

The commonest live example is the drop-in application: a fresh permission for one plot or one block within a larger consented scheme, granted while the wider scheme is being built out.

Before Hillside, drop-ins were used routinely to keep phasing flexible. After it, the risk is that the drop-in is materially inconsistent with the wider permission, so that building the drop-in prevents lawful completion of the rest.

Mitigating that takes deliberate drafting rather than optimism. The options in use include applying under section 73 to vary the parent permission so that the whole scheme remains internally consistent, securing a fresh permission for the entire remaining development rather than for one plot, and drafting the parent permission from the outset so that it is expressed as a series of severable phases with conditions that work independently.

Section 73B of the Town and Country Planning Act 1990, inserted by the Levelling-up and Regeneration Act 2023, was enacted to provide a route for varying an existing permission in these circumstances. Commencement of provisions in that Act has been staged, so check the current position on legislation.gov.uk before building a strategy around it.

Recording which permission was implemented

Most disputes in this area are evidential. Years later, nobody can say with confidence which permission the works were carried out under.

Fix that at the time. A short implementation file should contain the decision notice relied on, the discharge of any pre-commencement conditions with the approval letters, the notice of commencement where one was required, dated photographs of the works that constitute a material operation, the building control records and the contractor's programme showing the start date.

1. Decide, before any work starts, which permission you are implementing.
2. Discharge the pre-commencement conditions on that permission, not on another one.
3. Carry out a material operation that is authorised by that permission.
4. Photograph it, dated, with a plan showing where on the site it was.
5. Write a file note recording the decision and the evidence, and keep it with the title deeds.

That last step costs an hour and has resolved arguments that would otherwise have cost a scheme.

Checking before you start work

Where the position is doubtful and the money is real, apply for a certificate of lawfulness under section 191 or 192 of the 1990 Act. A certificate of proposed use or development is the only formal way to establish that what you intend to do is lawful, and it is a sensible expense on any site with a tangled permission history.

Pre-application advice is not a substitute. An officer's view is helpful and it does not bind the authority, and it will not assist against an enforcement notice.

The title review matters too. Overlapping red lines, land sold off since the original permission and third party interests all bear on whether a permission can still be carried out. A permission whose red line includes a strip the applicant sold to a neighbour in 2018 is not capable of implementation in accordance with its plans, however willing the council is.

Do the check at the point of purchase, and again before any spade goes in. The two moments produce different answers on sites where work has happened in between.

Where a fresh application is the answer, a Planning Statement setting out the full planning history, what has been implemented and why the new permission is needed does more than any amount of correspondence. Browse all 66 report types for the wider bundle. Two other procedural traps worth knowing about sit nearby: holding directions, which can suspend a decision the council has already resolved to make, and the deemed refusal appeal for non-determination, which starts a different clock entirely.

This is general guidance, not legal advice. Whether a particular permission remains capable of implementation is a question of fact and law on the specific site, and you should take advice from a planning solicitor before relying on any view of it.