The Law of Harmless Errors

Key Contacts: Alice Whittaker – Partner

“For a certain type of observer, the fate of a single roost containing a single bat will be viewed as a trivial basis for a debate about the validity of the planning permission. That is perhaps understandable at a superficial level but is a misconception. Obviously the issue isn’t trivial if you are the bat.”

In Doyle & Others v An Bord Pleanála & Others [2025] IEHC 158, the High Court determined that it would trivialise judicial review and be an exercise in self-indulgence to quash decisions merely because of things that ultimately made no difference (at least in the absence of a mandatory provision that compels such an approach).

Background

The judicial review (which is ongoing) relates to two planning permissions granted by An Bord Pleanála for a data centre, energy centre, and associated infrastructure (ABP-314474-22), and 110kV GIS substation, and two 110kV grid connection cables and associated infrastructure (ABP-313895-22) at a 60-hectare site near Ennis, County Clare.

The judgment, delivered on Friday 21 March 2025, relates solely to one issue, whether an error to which the Board admits is material enough to warrant invalidating and quashing the Board’s decision to grant permission.

The balance of legal issues pleaded by the applicant in the judicial review will be determined in subsequent stages of the proceedings.

The Admission of Error

The Board admitted that it had made an error and would concede to an Order quashing the decision, as it was concerned that it had “failed to identify, consider and assess the potential impacts of the Proposed Development on bat fauna“. The report of the Inspector appointed by the Board to report on the matter (on which the Board relied) stated, incorrectly that, in relation to bats, “no roosts were recorded during surveys“.

In fact, the revised Environmental Impact Assessment Report (EIAR) had identified that a survey of one of the buildings (Building 6C) had revealed a single bat roost for a single Leisler’s Bat. The EIAR identified significant overall potential for bats and bat roosts in old farm buildings, stone walls, trees, and hedgerows within the proposed development site.

The developer opposed the quashing of the permission, arguing that it would be a disproportionate and unnecessary response to what amounted to a harmless error.

The applicant for judicial review argued that the error was significant, particularly as it related to a species that is strictly protected under Annex IV and the destruction of roosts is specifically prohibited under Article 12 of the Habitats Directive.

Harmless Error – Legal Principles

The judgment helpfully summarises the key legal authorities on the concept of a harmless error in decision-making, both in the domestic legal and EU law context.

The Court discerned the following legal principles from the case law:

1. A decision should not be quashed for error (including in application of EU law) if the error was harmless and did not materially affect the result. It would trivialise judicial review and be an exercise in self-indulgence to quash decisions because of things that made no difference, at least in the absence of a mandatory provision that compels such an approach.
2. Whether an error would have affected the result is a determination that must be made by the Court. The Court can make this determination based on the evidence, including evidence provided by an interested party, such as the developer.
3. The Court should exclude any reasonable possibility that the error would have made a difference to the actual outcome, although absolute certainty is not required.
4. The party asserting harmlessness carries the burden of proof.
5. Whether public participation was materially compromised is also relevant.
6. Where by contrast the error would have had a material effect on the outcome: (i) any breach of EU law should normally be remedied by the quashing of the decision (certiorari); and (ii) where the error relates to purely domestic law the court has a wider discretion although is not fully at large.

Application of legal principles to the facts

The evidence established that bats swap roosts regularly (every two to ten days for Leisler’s Bat), that the single roost in Building 6C contained just one bat, and that as bats are highly mobile, this single roosting bat would likely have moved to a different location by the time the proposed development is carried out.

While bat roosts are strictly protected from destruction under Article 12(1)(d) of the Habitats Directive, destruction occurs at the point of executing the permission, not at grant. The assessment properly factored in bat mobility between application and execution.

The relevant Bat Guidance establishes that the proper approach to assessing impacts should consider potential roost features overall, rather than focusing on any single confirmed roost, and this was the approach taken by the ecological experts, Scott Cawley, in their risk assessment for the proposed development.

The EIAR identified that the site contains several potential roost features and anticipated the possibility of new roosts being established between the dates on which surveys were carried out and the development is undertaken following the grant of planning permission. As mitigation, the EIAR committed to pre-construction checks for bats in specific buildings and locations of potential roost features, and the inclusion of protocols for bat exclusion or removal by licensed specialists if bats are found. If bats or their roosts are identified, the developer would seek a Derogation Licence from the Minister for Housing, Local Government and Heritage (NPWS) for the safe and humane removal and relocation of any species present in the buildings by a suitably qualified ecologist.

These mitigation measures were ultimately made binding on the developer through planning conditions recommended by the Board’s Inspector and included by the Board. The approach to mitigation was precautionary in nature, and would have been identical whether dealing with confirmed or potential roosts, as the measures were designed to address both scenarios.

Public participation was not undermined, as the EIAR correctly stated the position with respect to the single bat roost in Building 6C, and the Court also noted that there were no submissions or observations throughout the application and appeal process with regard to significant effects on bats or their roosts.

The fact that the Board determined that it should concede to a quash of its decision is not determinative, and the question of whether an error is harmless is a matter for the Court, based on the totality of the evidence.

The test is whether reasonable doubt can be excluded regarding a different outcome, not whether the Board would have “definitely” made the same decision. The Court is entitled to form this view based on the logical consequence of the evidence.

“the potentiality necessarily includes the actuality“.

The EIA accounted for potential bat roosts in its surveys, assessments, and proposed conditions, and therefore the actual occupation status of any roost at a given time did not materially affect the outcome. The mitigation measures required by the planning conditions adequately addressed the impacts on bat populations regardless of whether the particular bat roost was documented in the Inspector’s report.

Observations on Legal Advocacy

The developer’s legal submissions were praised for their “remarkable efficiency”, and the Court re-stated its desire that practitioners in the Planning and Environmental List would focus on the quality rather than quantity of their legal points, and the value of time-limited hearings and expedited procedures in judicial proceedings.

Future Considerations

This judgment relates solely to ‘module 1’ of a modular hearing in which there are further substantive legal arguments to be addressed, including (in summary):

• whether the EIA could be validly determined in the absence of a derogation licence from the NPWS for the removal of bat roosts and/or disturbance of bats;
• whether the Board complied with section 15 of the Climate Action and Low Carbon Development Act 2015, as amended (and as discussed in a previous article);
• whether the Board’s decision that the proposed development would have potentially positive environmental impacts was irrational, given that it was based on a future switch to sustainable renewable gas, which would require such fuel to be available in sufficient quantities during the operational lifetime of the data centre, which the applicant considers unlikely;
• whether the Board acted irrationally in not requiring mitigation of the greenhouse gas emissions from the proposed data centre;
• whether the Board gave too great weight to the Government Statement on the Role of Data Centres in Ireland’s Enterprise Strategy July 2022 (Data Centre Strategy), in setting the policy framework for data centres in Ireland, where that strategy has not been the subject of a Strategic Environmental Assessment (SEA), and has therefore not been given the status of a ‘plan or programme’ to which the SEA Directive applies; and
• whether the Board failed to ensure that the permission would not cause a deterioration of water quality status, contrary to the Water Framework Directive (an argument that is discussed in a previous article).

The State’s adoption of the Data Centre Strategy is also challenged in these proceedings on the basis that the State failed to ensure that it was subject to a prior assessment and determination in accordance with the SEA Directive.