Avoiding the 'Unreasonable Behaviour' costs award
From February 2026, PINS has widened what counts as unreasonable behaviour. With the 'Submit Once' model, a misleading claim carries real financial consequences.
David Robinson
Founder, Planning Appeals
In planning appeals, "unreasonable behaviour" isn't just a matter of opinion — it's a financial liability. As of February 2026, the Planning Inspectorate has widened the net for what constitutes unreasonableness, and the costs will be falling on the parties involved.
What is changing?
The new guidance clarifies that submitting inaccurate, misleading, or poorly evidenced claims is now a fast track to an Award of Costs. If a Local Authority or an Appellant causes the other side to incur wasted expense — for example, by having to hire a specialist to debunk a "hallucinated" or unverified claim — the Inspector can order that party to pay the other's professional fees.
Why this matters
With the "Submit Once" model, you cannot retract or fix a misleading statement once the appeal is underway. Your initial submission carries the full weight of potential financial penalty. Being able to verify everything you submit has never been more important.
How to adapt
- Verify every fact: Don't take a summary at face value. If you are going to cite sources or relevant cases, don't rely on AI summaries. Professional bodies and PINS have issued guidance regarding the use of this emerging technology.
- Use the "Source" button: Every extraction on planningappeals.co.uk is a research signal that must be verified, and can link directly to the source text to help you meet the "reasonableness" threshold. Cite sources with confidence and strengthen your argument today.
Source check: See Section 3.2.2 regarding "Unreasonable Behaviour" and costs in the new PINS procedural guidance for applications dated on or after 1 April 2026: https://www.gov.uk/guidance/planning-appeals-procedural-guide-for-appeals-relating-to-applications-dated-on-or-after-1-april-2026#introduction
PINS has also issued guidance on the use of artificial intelligence in casework evidence: https://www.gov.uk/guidance/use-of-artificial-intelligence-in-casework-evidence
Strengthen your next argument
Search 200,000+ appeal decisions. Inspector reasoning, traced back to the original application.
Related articles
Why verifiability is the new standard
In planning, 'trust me' is not a valid citation. With the 2026 PINS changes, the ability to trace and verify every argument has never been more important.
How to use data to strengthen a planning argument
From 1 April 2026, your planning submission must do all the heavy lifting. Here's how targeted planning intelligence — and correct policy interpretation — can sharpen your argument from the start.
Consistency & costs
The 2026 PINS guidance shifts the entire burden of defence onto the Officer's Report and Committee Minutes. Transparency is now a financial necessity.