Harmless Error and Material Contravention: Certiorari Limits for Have-Regard-To Local Area Plans

Introduction

This commentary examines the High Court’s decision in Ryanair Designated Activity Company v An Bord Pleanála [2025] IEHC 194 (Humphreys J., delivered 4 April 2025). The applicant, Ryanair DAC, challenged a grant of planning permission for an underpass at Dublin Airport on a multiplicity of grounds—ranging from alleged breaches of the EU Water Framework Directive to climate and habitats law, and finally to a purely domestic point concerning an alleged mis-phrasing in the Inspector’s report on contravention of the Local Area Plan (“LAP”). By the time of the leave-to-appeal hearing, only the LAP point remained. The core issue before Humphreys J. was whether a mere semantic slip in describing a contravention of the LAP as “immaterial” rather than “justified” could amount to a material error warranting certiorari in the absence of any statutory provision (in particular, s. 37(2) of the Planning and Development Act 2000) making the distinction legally consequential.

Summary of the Judgment

The Court rejected the application for leave to appeal. It held that:

Ryanair’s sole remaining ground—an infelicity in the inspector’s wording—did not give rise to any substantive legal error because there was no statutory requirement to treat an LAP contravention as “material” or “immaterial” under s. 37(2) of the 2000 Act.
Even if an error had occurred, it was “harmless”—it made no difference to the outcome, since the inspector explicitly treated the contravention as justified and the board’s jurisdiction and discretion were unaffected by the choice of words.
The criteria for leave to appeal in planning judicial review cases require a real, determinative legal point of public importance. A purely semantic or discursive error that does not change the decision-making process fails the “determinative difference” test.
Decisions should be read so as to give them validity where a sensible reading is available. The inspector’s report, read as a whole, plainly addressed justification for the contravention and thus cured any semantic slip.

Analysis

Precedents Cited

The judgment draws extensively on both domestic and EU jurisprudence concerning harmless error, the interpretation of administrative decisions, and the threshold for leave to appeal in judicial review of planning decisions.

Materiality and harmless error doctrines (UK and EU):
- Walton v. Scottish Ministers [2012] UKSC 44
- Champions v. North Norfolk DC [2015] UKSC 52
- Gemeinde Altrip v Land Rheinland-Pfalz (C-72/12) (Opinion A.G. Cruz Villalón, and subsequent CJEU judgment)
Reading decisions as valid where possible:
- R. (Champion) v. North Norfolk DC [2015] UKSC 52
- Rostas v. DPP [2021] IEHC 60
- St. Margaret’s Recycling v. An Bord Pleanála [2024] IEHC 94
Leave to appeal criteria in planning judicial review:
- Concerned Residents of Treascon and Clondoolusk v. An Bord Pleanála [2024] IESC 28
- GOCE Ltd v. An Bord Pleanála [2025] IEHC 43
- S.A. v. Minister for Justice and Equality (No. 2) [2016] IEHC 646
- Monkstown Road Residents Association v. An Bord Pleanála [2023] IEHC 9

Legal Reasoning

The High Court’s reasoning unfolds in two complementary threads:

Assumption and statutory context:
Ryanair’s argument assumed that the distinction between “material” and “justified” contravention of an LAP has legal significance. That assumption, objectively necessary for its point to work, implies the application of s. 37(2) of the Planning and Development Act 2000. The Court had already rejected the applicability of s. 37(2) in Ryanair v. An Bord Pleanála (No. 1) [2025] IEHC 74. Absent s. 37(2), neither materiality nor immateriality of an LAP contravention affects the board’s discretion or jurisdiction.
Harmless error and purposive reading:
Even if the inspector’s report had used a less felicitous word (“immaterial”), the substantive judgment demonstrates that there was no misunderstanding of the LAP’s content. More importantly, the inspector expressly treated the contravention as “not a reason to refuse permission” and addressed justification in a broader context. Under settled case law, administrative decisions should be read so as to uphold validity where a coherent interpretation is available. A semantic slip that makes no material difference cannot sustain certiorari.

Impact

This decision cements the application of the harmless error doctrine in Irish planning judicial review and clarifies the limited legal effect of “have-regard-to” instruments such as Local Area Plans:

It confirms that a local authority’s or board’s failure to comply strictly with a “have-regard-to” document is not in itself a jurisdictional defect.
It reinforces the requirement that any alleged error must be shown to make a determinative difference to the decision outcome before leave to appeal can issue.
It underscores the courts’ duty to read decisions so as to preserve validity where reasonably possible, discouraging hyper-technical challenges based on word choice alone.
Future appellants will need to demonstrate both a statutory or constitutional breach and a real, material impact on the decision-making process to satisfy the leave-to-appeal criteria.

Complex Concepts Simplified

Have-regard-to document

A statutory plan (such as a Local Area Plan) which a decision-maker must consider but is not strictly bound to follow. Non-compliance with it does not automatically invalidate a planning decision.

Certiorari

A prerogative remedy whereby a superior court quashes an inferior decision on grounds of illegality or procedural unfairness.

Harmless error

An error in law or procedure that does not affect the substantive outcome of a decision. Courts will not quash a decision for a harmless error.

Section 37(2) of the Planning and Development Act 2000

A statutory provision that makes “material contravention” of certain plans a legal ground for refusal of permission or appeal. Its non-application here meant that materiality vs. justification had no statutory bite.

Leave to appeal criteria

A planning judicial review can only proceed to appeal if the point:

Properly arises on the pleadings;
Is a pure question of law;
Is of exceptional public importance;
Is determinative of the outcome;
Is brought within the statutory time.

Conclusion

Ryanair DAC v An Bord Pleanála [2025] IEHC 194 establishes an important precedent on the interface between judicial review, harmless error doctrine, and the treatment of “have-regard-to” documents in Irish planning law. The decision clarifies that:

Semantic slips or non-material mis-phrasing in an inspector’s report do not suffice to found certiorari where no statutory provision renders them consequential.
Courts are duty-bound to read administrative decisions so as to uphold validity where a sensible interpretation is available.
Appellants must demonstrate a real, determinative legal error of public importance and actual impact on decision-making to obtain leave to appeal.

By reinforcing the harmless error principle and the delineation of jurisdictional limits in planning judicial review, this judgment promotes certainty, efficiency, and substance-over-form in the adjudication of complex infrastructure and environmental challenges.