In planning law, the legal error is not that the decision-maker treated policy as decisive. Planning policy is part of the legal framework within which discretion is exercised. The real question is whether the policy was understood and applied according to its own terms.
A policy may be misconstrued where its words are read too widely, too narrowly, or without regard to their planning context. A criterion intended to guide judgment may be treated as if it imposed an automatic refusal. A policy which requires assessment may be applied as though it leaves no room for assessment. At that point, the complaint is no longer that the Tribunal reached an unattractive planning conclusion – it is that it reached that conclusion through a legally wrong route.
The same applies to qualifying language. Words such as “normally”, “unless”, “where appropriate”, “having regard to”, “subject to”, or “in exceptional circumstances” are not ornamental. They shape the legal operation of the policy. If the decision-maker ignores those words, it is not applying the policy as written, but a simplified and stricter version of it.
Nor may facts be forced into a policy conclusion which the policy, properly construed, cannot sustain. The court should not reweigh the planning evidence. But once the facts found by the Tribunal are accepted, there may still be a legal question: were those facts capable, in law, of satisfying or breaching the policy criterion relied upon? If not, the error is not merely factual. It is an error in the legal application of policy.
The dividing line is therefore this: disagreement with the Tribunal’s planning evaluation is usually a matter of fact or merits. But misunderstanding the policy, ignoring its qualifications, converting discretion into prohibition, or attaching to the facts a legal consequence which the policy does not permit, is a point of law. That is where planning judgment crosses into legal error.
