Tailpiece conditions and why they are unlawful
A condition that lets the authority approve something materially different from the permission, by correspondence and without publicity, is unlawful. Here is how to spot one and what to do about it.
A tailpiece condition planning officers still draft looks harmless on the page: the scheme shall be carried out in accordance with the approved plans, unless otherwise agreed in writing by the local planning authority. Those last eight words are the tailpiece, and where they allow the authority to approve something materially different from what was permitted, they are unlawful. The High Court has quashed permissions over them, because a condition cannot hand an authority a private power to permit development that the public never saw.
The wording survives because it feels pragmatic. Everyone wants flexibility. The problem is that this is flexibility of the wrong kind.
What a tailpiece looks like
The construction is a condition that states a requirement and then qualifies it with an open-ended escape.
"The development shall be carried out in accordance with drawing numbers listed below, unless otherwise agreed in writing."
"The approved materials shall be used, unless otherwise agreed in writing by the local planning authority."
"No more than 48 dwellings shall be constructed, unless otherwise agreed in writing."
The third is the clearest example of the problem. A permission for 48 dwellings with that tailpiece is, on its face, a permission for any number of dwellings the authority later agrees to in correspondence, with no application, no publicity and no right of appeal for anybody.
Why open-ended wording is objectionable
Four of the six tests that a condition has to satisfy are strained or broken by a tailpiece.
Precision fails first. A condition has to tell the reader what is required, and one that may be set aside by unrecorded agreement does not.
Enforceability fails next. An officer attempting to enforce the condition has to prove that nothing was agreed in writing by anybody at the authority at any time, which is a negative that is difficult to establish on a file that has been open for a decade.
Necessity is questionable, because the system already contains the mechanisms for change: an application under section 73 to vary a condition, and a non-material amendment under section 96A. A tailpiece exists to avoid both.
And reasonableness fails in the wider sense, because the statutory route for changing a permission carries publicity, consultation and a right of appeal, and the tailpiece route carries none of them. Third parties lose their ability to comment on a material change. That is the point the courts have fastened on.
The effect on certainty
A permission is a public document that binds the land. Anyone buying the site, lending against it or living next to it should be able to read the decision notice and know what may be built.
A tailpiece breaks that. The reader has to find out whether anything was "otherwise agreed", which means a file search, an information request, or an assumption. On a site changing hands years after the grant, that history is often lost.
It also creates a trap for the developer. Reliance on an officer's email agreeing a change, where the change was material, does not make the development lawful, and the resulting building may be unauthorised despite an apparently helpful exchange. Our note on the six tests a condition has to meet sets out the framework the courts apply.
The distinction that matters
Not every condition referring to later approval is a tailpiece, and this is where the subject gets muddled.
A condition requiring details to be submitted and approved is perfectly lawful. "No development above slab level shall take place until details of external materials have been submitted to and approved in writing by the local planning authority, and the development shall be carried out in accordance with the approved details" is a proper condition. It identifies something not yet fixed and provides a route to fix it.
A tailpiece is different in kind. It takes something that has been fixed by the permission and allows it to be unfixed by agreement.
| Lawful | Unlawful |
|---|---|
| Approves outstanding details later | Allows approved matters to change later |
| Scope is defined by the condition | Scope is open ended |
| Produces a decision on an application | Produces correspondence |
Ask one question of any condition: does this allow the authority to approve something materially different from what was applied for. If it does, it is a tailpiece.
Acceptable ways to build in flexibility
Flexibility is a legitimate objective and there are proper routes to it.
Where quantum may move, apply for a range or use parameter plans with maximums and minimums, so the permission itself accommodates the variation. Where a detail may change, leave it to a details condition rather than approving it and then qualifying the approval. Where a tolerance is needed on levels or dimensions, state the tolerance numerically in the condition.
Where the change is minor in substance, section 96A exists and is quick. Where it is more than minor but the development remains in substance what was permitted, section 73 is the route, and it produces a new permission that a purchaser can read.
A well-drafted Planning Statement can head this off by proposing condition wording at application stage, including the tolerances the scheme needs. Officers under time pressure frequently adopt suggested wording.
Rewriting one before the decision is issued
The window is short and most applicants miss it.
Draft conditions normally appear in the officer's report, which is published before a committee meeting and is often available on request before a delegated decision. Read them. Where a tailpiece appears, write to the case officer with alternative wording that achieves the same practical flexibility lawfully, usually by converting it into a details condition or by stating a numeric tolerance.
Where the condition is a pre-commencement one, there is a further lever: the authority has to obtain the applicant's written agreement before imposing it, and that exchange is the moment to propose better wording.
Officers are not attached to tailpieces. They are attached to not having to deal with the scheme again, and a condition that gives them a defined approval route achieves the same thing.
Living with an existing permission that carries one
If the permission is already granted, three positions are worth distinguishing.
For an immaterial change, section 96A is available regardless of the tailpiece and produces a clean record. Use it.
For a material change, do not rely on the tailpiece. Apply under section 73, accepting that the condition's invalidity does not make the change lawful. Where the reserved matters route is open on an outline permission, our note on the five reserved matters covers what can still be settled that way.
For a permission you are buying, raise it in enquiries. A tailpiece is a defect in the title to the permission, and the seller should be asked what, if anything, was ever "otherwise agreed", with the correspondence produced.
One honest uncertainty: whether an unlawful condition can be severed from a permission, leaving the rest standing, depends on the facts and is not something to assume either way without advice.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
Browse the 66 report types to see which documents support a section 73 application to vary a condition.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is a tailpiece condition?
A condition that states a requirement and then qualifies it with open-ended wording such as unless otherwise agreed in writing by the local planning authority. Where that wording would allow the authority to approve something materially different from what was permitted, without an application or publicity, the condition is unlawful.
Is every condition mentioning later approval a tailpiece?
No, and the distinction matters. A condition requiring details to be submitted and approved before a stage of work is perfectly lawful, because it identifies something not yet fixed and provides a defined route to fix it. A tailpiece takes something the permission has already fixed and allows it to be unfixed by correspondence.
Can I rely on an officer's email agreeing a change under a tailpiece?
Not for a material change. The invalidity of the condition means the agreement does not authorise the development, and the resulting building may be unauthorised despite the exchange. For an immaterial change use section 96A; for a material one use section 73, which produces a permission a purchaser can actually read.
How do I get a tailpiece removed before the decision?
Read the draft conditions in the officer's report, which is published before committee and often available before a delegated decision. Write to the case officer proposing alternative wording that achieves the same flexibility lawfully, usually a details condition or a stated numeric tolerance. Officers commonly adopt suggested wording when it is offered early.
What should a buyer do about a permission carrying a tailpiece?
Raise it in pre-contract enquiries and ask the seller what, if anything, was ever agreed under it, with the correspondence produced. A tailpiece makes the permission uncertain on its face, since the reader cannot tell from the decision notice what the permission now authorises without searching the planning file.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.