What you need to know
- The Supreme Court has provided clarification on the de minimis principle and doctrine of harmless error in planning law.
- Courts should not quash public body decisions for inconsequential or immaterial mistakes.
- A key consideration is whether the underlying purpose of the relevant statutory rule has been met.
- It is important to bear in mind that judicial review is a discretionary remedy.
- Generally, legislation does not provide for what the effect of non-compliance with a statutory requirement should be. Instead, the courts must decide this.
Not every mistake in a statutory process should result in a public body’s decision being quashed. That is the central message from the Supreme Court’s judgment in O’Donnell.[1]
The case involved a judicial review challenge to a local authority decision to re-zone land. The Supreme Court held that the alleged error made by the local authority "was an adequate compliance" with the relevant statutory rule. It also held that, even if an error was made, it was too insubstantial and trivial to justify quashing the decision.
What happened?
The judicial review applicant sought to challenge a decision by Dublin City Council to re-zone land. Its planning consultant made a submission on its behalf during the public consultation process on re-zoning. The local authority was statutorily required to prepare a report on the submissions it received. In the report, it was required to identify all persons who made submissions. In this case, the local authority identified the applicant’s planning consultant, rather than the applicant itself, as having made a submission.
While the High Court found that this breached the requirement and quashed the rezoning decision, the Supreme Court disagreed and overturned that ruling. The Supreme Court found the purpose of the list was administrative. It was to record who made submissions so as to show they had been accounted for. It held this requirement could be satisfied by listing either the name of the applicant or its planning agent. On this basis, the Supreme Court held that the listing of the applicant’s planning consultant was an adequate compliance with the statutory requirement.
The Supreme Court also held that, even if it was an error, it was too insubstantial and trivial to justify quashing the decision. The Court then embarked on a consideration of the doctrine of harmless error in planning law.
Main principles of ‘harmless error’
The first question is whether the legislation expressly says, or clearly implies, that non-compliance makes a decision invalid. If it does, the court must implement that consequence.
If invalidity is not expressly required, the court must look at the practical effect of non-compliance. This involves considering all the circumstances and asking:
- Has there been substantial compliance?
- Is the breach technical or trivial?
- Has anyone suffered material prejudice?
- Does the public interest require the decision to be invalidated?
A defect is more likely to be harmless where the underlying objective of the statutory rule has still been met. In O’Donnell, the local authority had recorded the submission, summarised it and responded to it. The applicant also knew that its own agent had made the submission.
The Supreme Court highlighted that judicial review is a discretionary remedy. Mr Justice Hogan held that:
The truth of the matter is that the court will invalidate an order only if the right remedy is sought by the right person in the right proceedings and circumstances and, it might be added, at the right time… Save possibly in the quite exceptional cases where the illegality is patent, an administrative decision remains valid unless and until it is set aside”.
However, the Court also stressed that statutory obligations must be respected. Courts should not excuse material non-compliance which affects the integrity of a decision or undermines the rights of affected people. Mr Justice Woulfe noted:
It is the duty of the Court to give effect to that which the Oireachtas has ordained should be done… The Courts should not generally be asked to excuse or disregard what the Oireachtas has prescribed should be done”.
How ‘harmless error’ should be applied in practice
Some of the key principles to bear in mind when applying the doctrine of harmless error include:
- Identify the purpose of the requirement, not just the wording. Ask what the rule was designed to achieve.
- Check whether the decision-maker substantially achieved that purpose, even if the process was imperfect.
- Ask whether the error made any real difference to participation, fairness, the information before the decision-maker or the outcome.
- Look for actual or realistically possible prejudice, rather than relying on abstract assertions of unfairness.
- Keep proportionality in mind. Quashing a decision may be wrong where the defect is technical, no one was misled and the decision-making process remained sound. However, quashing remains appropriate where:
- The failure is material
- The statutory purpose is compromised, or
- Third-party rights may have been affected.
Endorsement of harmless error
Provided the doctrine of harmless error is applied appropriately, the Supreme Court has held it should continue to be the guiding principle in cases like O’Donnell. Mr Justice Hogan held that the principle is:
the one which best complies with the requirements of the rule of law and the objective of safeguarding democratic legitimacy”.
Non-compliance with statutory requirements may be excused if the underlying statutory objective is not compromised and where no material prejudice is caused.
Conclusion
The Supreme Court’s decision in O’Donnell is a useful reminder that judicial review is not a search for perfection. Public bodies must comply with statutory requirements. However, courts will look carefully at whether an alleged defect actually matters. For decision-makers, the practical lesson is to:
- Design processes that meet both the letter and purpose of the legislation
- Document compliance clearly, and
- Be ready to explain why any procedural error did not affect fairness, participation or outcome.
For more information and expert guidance, please reach out to a member of our Planning & Environment team.
[1] Pat O’Donnell & Co v Dublin City Council [2026] IESC 36
