The appeal is now argued on evidence you've already given

§1What actually changed

From 1 April 2026 the Planning Inspectorate operates a new procedural guide for appeals relating to applications dated on or after that date. Two things in it matter.

The first is procedural: a Part 1 expedited written representations procedure is now the default route for most appeals. Faster, tighter, less room for the elaborate.

The second is the one that changes behaviour. An appellant cannot introduce evidence that was not already before the local planning authority — unless there has been an exceptional material change in circumstances. A new policy. A relevant court judgment. A relevant appeal decision.

Not "unless it's important". Not "unless you have a good reason". Exceptional.

§2What it kills

There was a way of working that made a certain kind of sense. Submit an application without the expensive supporting work — no daylight assessment, no viability appraisal, no heritage statement beyond the minimum. See what the council objects to. If refused, commission the reports that answer the actual objections and put them in at appeal, where an Inspector reads them fresh.

It saved money on schemes that sailed through. It concentrated expenditure on the fights that were real.

It no longer works. If the daylight assessment wasn't before the officer, it generally can't be before the Inspector. The appeal is fought with the file the council had.

§3The transitional trap

Here is the part that will catch people this year, and it's worth being precise about.

The new guide applies to appeals relating to applications dated on or after 1 April 2026. Applications dated on or before 31 March 2026 fall under the previous procedural guide.

So through 2026 and well into 2027, two regimes run side by side — and which one governs your appeal has nothing to do with when you appeal. It is fixed by the date of the application. An application submitted in March 2026, refused in the autumn, appealed in the winter, is on the old rules. One submitted in April is not.

If you are advising on an appeal right now, that date is the first thing to check, and it is not intuitive.

§4What it means if you haven't applied yet

The application is now the last moment at which you can make your case.

That reframes the economics of supporting evidence. The reports that used to look like optional expenditure at application stage are now the only opportunity to get that material into the process at all. Commissioning a survey after refusal buys you a document you may not be permitted to use.

It also raises the value of getting the objections right in advance. The whole point of the old approach was that the council told you what to argue about. Now you have to anticipate it — which means reading the constraint layer, the planning history, the recent decisions of that authority on comparable schemes, and the policies the officer will actually apply.

That is a planner's job rather than a designer's, and this rule change is the clearest argument for that distinction anyone has produced in years.

§5What it means if you're already refused

The strategic question has narrowed to one thing: can the case be won on the material the council already had?

If the file contains the evidence, appeal. If the reasons for refusal identify a gap that could only be filled by material you never submitted, an appeal is likely to fail on that gap — and the better route is usually a fresh application containing the missing evidence, or a negotiated amendment.

That assessment is worth doing properly before spending on an appeal, because the appeal deadlines are unforgiving and the appeal fee and professional time are not recoverable. Twelve weeks from a householder or minor commercial refusal. Six months from most others. Twenty-eight days from an enforcement notice.

§6The exceptional circumstances aren't nothing

It's worth not overstating this. The exception is real: policy changes, relevant judgments, relevant appeal decisions.

And 2026 has been an unusually busy year for exactly those things — the Planning and Infrastructure Act 2025 is being commenced in stages, biodiversity net gain changed twice in a fortnight over the summer, and a revised NPPF has been expected since the spring. Where a scheme was determined under a policy position that has since moved, there may genuinely be something to say.

That is a narrow door, not an open one. But it is a door, and it's worth checking before assuming it's shut.