Factual and Procedural Background
The applicants sought judicial review of a planning decision granting permission for 21 wind turbines and ancillary works at Castlebanny, County Kilkenny. The development was made under the strategic infrastructure development regime and affected part of the South Leinster Way. [1][2][3]
The planning application was submitted on 28 January 2021. The decision-maker granted permission on 26 September 2022. The applicants commenced proceedings on 21 November 2022. Earlier High Court and Supreme Court decisions addressed the timing of the proceedings, and the Supreme Court remitted the matter to the High Court. [4][5][6][7][8][9]
Following earlier judgments, the live issues were confined principally to whether the appropriate assessment was legally defective because site-specific conservation objectives were absent for the Kingfisher and Freshwater Pearl Mussel, and whether the State had failed to establish required conservation objectives and measures. [10][11][12][13]
The High Court held that the decision-maker had erred in conducting an appropriate assessment without the relevant site-specific conservation objectives, but considered that the error had no material effect on the assessment or outcome. [14][15][16]
Legal Issues Presented
- Whether the absence of site-specific conservation objectives for the Kingfisher and Freshwater Pearl Mussel invalidated the appropriate assessment and required certiorari. [17][18][19]
- Whether the State had failed to establish required conservation objectives and conservation measures under the Habitats Directive. [20][21][22][23][24][25][26]
- Whether the identified legal error was harmless and whether the court should exercise its discretion to refuse certiorari. [27][28][29][30]
- Whether declaratory relief should nevertheless be granted. [31][32][33]
- Whether a reference to the Court of Justice of the European Union was necessary. [34][35][36][37]
Arguments of the Parties
Applicants' Arguments
- The applicants argued that there were no relevant site-specific conservation objectives when the decision was made and that the appropriate assessment was therefore invalid. [38][39][40][41]
- They argued that the absence of conservation objectives created a jurisdictional defect requiring certiorari, and disputed the application of harmless-error principles. [42][43][44][45][46]
- They contended that the absence of conservation measures also entitled them to relief. [47][48][23][24][25][26]
- They sought a reference to the CJEU concerning whether relief could be withheld where there was no valid appropriate assessment. [36]
Decision-Maker's Arguments
- The decision-maker accepted that the later CJEU judgment identified a legal error, but argued that the error was harmless because the later conservation objectives would not have altered the assessment or decision. [49][27][50][28]
- It argued that certiorari was discretionary and that the absence of material environmental consequences justified refusing it. [27][28][51]
State Respondents' Arguments
- The State respondents submitted that national procedural autonomy permitted the court to grant limited relief, subject to equivalence and effectiveness. [52][53]
- They accepted that the State had lacked relevant site-specific conservation objectives at the material time, but argued that no further relief was warranted. [53][54]
- They maintained that conservation measures were in place and that the applicants had not pleaded or evidenced their inadequacy. [48][55][56][57]
Notice Party's Arguments
- The notice party accepted that a stage-two appropriate assessment could not validly be completed without previously adopted site-specific objectives, but argued that this did not determine the remedy. [58][59]
- It argued that relevant objectives for the SAC existed in 2011 and that the later material merely updated scientific and taxonomic information. [59][60][61][62]
- It relied on uncontested expert evidence that applying the later objectives would not alter the Natura Impact Statement, the appropriate assessment, or the planning decision. [63][64][65][66][15][16]
Table of Precedents Cited
| Precedent | Rule or Principle Cited For | Application by the Court |
|---|
| Save the South Leinster Way & Another v. An Bord Pleanála [2024] IESC 55 | The leave application was not out of time and the matter was remitted. | Recorded as part of the procedural history. [9] |
| Amariei v. Chief Appeals Officer [2026] IESC 22 | Judicial review concerns legality rather than merits; discretion is bounded by principle. | Used to define the court's restrained and discretionary role. [67][68][69][70] |
| Coolglass Wind Farm Ltd v. An Coimisiún Pleanála [2026] IESC 5 | Even an error affecting vires does not automatically require certiorari. | Applied to distinguish legal error from the discretionary remedy of quashing. [71][72][73][74][75] |
| Concerned Residents of Treascon and Clondoolusk v. An Bord Pleanála [2024] IESC 28 | Applicants are confined to their pleadings and complex EU-law arguments must be clearly pleaded. | Applied to reject unpleaded arguments concerning conservation measures. [76][77][78][79] |
| An Taisce v. An Bord Pleanála & Ors. [2022] IESC 8 | The applicant generally bears the burden of proving an environmental-assessment defect. | Applied to the applicants' failure to establish a defect in conservation measures. [80][81][82] |
| O'Donnell v. Dublin City Council [2026] IESC 36 | Harmless-error principles and the two-stage inquiry into invalidity and discretion. | Supported the conclusion that not every breach produces automatic nullity. [42][43][83][84][85] |
| Joined Cases C-27/25 and C-356/25, Knocknamona and Massey | A valid appropriate assessment cannot be conducted without previously adopted site-specific conservation objectives specific to the protected site. | The court accepted that the planning decision contained a legal error on this basis. [86][87][88][89][14] |
| Gemeinde Altrip and Others v Land Rheinland-Pfalz, C-72/12 | A procedural defect need not lead to annulment if it could not have affected the outcome; the court may rely on developer evidence. | Applied as the principal EU-law support for harmless error. [90][91][92][93][94] |
| RAS Medical Ltd v. Royal College of Surgeons in Ireland [2019] IESC 4 | An evidential conflict may be resolved against the party bearing the burden where there is no cross-examination. | Applied because the applicants did not contradict or test the relevant evidence. [95][96][97][98] |
| G. v. DPP [1994] 1 I.R. 374 | Judicial review is discretionary and the court considers the importance or triviality of the breach. | Used in assessing whether certiorari was proportionate. [91][99][100][101] |
| O'Connell v. Behan [2021] IECA 186 | Discretion includes conduct of the applicant, practical value of relief and proportionality. | Used to structure the discretionary analysis. [102][103][104][105] |
| Pat O'Donnell & Co. v. Dublin City Council [2026] IESC 36 | Relevant factors include substantial compliance, triviality, prejudice and public interest. | Applied to the court's assessment of harmlessness and proportionality. [85][106][107] |
| Commission v. Ireland (Derrybrien Wind Farm), C-261/18 | Material breaches of EU environmental law should normally be remedied by certiorari. | Distinguished because the court found no material effect here. [108] |
| B. v. Child & Family Agency & Ors. [2025] IESC 2 | Identified criteria for declaratory relief. | Applied in granting a declaration concerning the legal error. [32][109][110][111] |
| Consorzio Italian Management and Catania Multiservizi SpA v Rete Ferroviaria Italiana SpA, C-561/19 | No reference is required where the point is acte clair or acte éclairé. | Applied in refusing a CJEU reference. [112][113][114][115][116][37] |
| Eco Advocacy v. An Bord Pleanála [2025] IESCDET 74 | A reference is unnecessary where the point does not arise on the pleaded facts. | Supported refusal of the proposed reference. [117][35][118] |
| R. (Bradbury) v. Brecon Beacons National Park Authority [2025] EWCA Civ 489 | A planning decision may stand where the outcome would not have been substantially different had the omitted assessment been available. | Illustrated the comparable harmless-error approach. [119][120][121] |
| Wells, C-201/02 | National procedural autonomy is subject to EU-law requirements. | Supported the compatibility of discretionary domestic remedies with EU law where no material effects exist. [122][123] |
| Save The South Leinster Way v. An Coimisiún Pleanála (No. 2) [2025] IEHC 541 | Declarations are equitable and ordinarily concern a specific legal error. | Used in formulating the criteria for declaratory relief. [124][125][126][127] |
Court's Reasoning and Analysis
The court treated the case as one involving a proven legal error but no demonstrated material consequence. Judicial review was described as concerned with legality rather than merits, and certiorari as a discretionary remedy rather than an automatic consequence of every legal breach. [67][128][129][130]
The court accepted that site-specific conservation objectives were absent for the Kingfisher until 2 July 2024 and for the Freshwater Pearl Mussel until 6 June 2025. It also accepted that the decision-maker erred by conducting an appropriate assessment without those objectives. [131][132][133][134][135][14]
The court then considered whether the error affected the result. The notice party's expert updated the Natura Impact Statement using the later objectives and concluded that the development would still not adversely affect the integrity of the relevant European sites. That evidence was uncontested and was not tested by cross-examination. [15][136][137][16][138][139]
The applicants did not provide expert evidence identifying any environmental consequence or showing that the decision would have been different. The court therefore found that the opposing parties had discharged the burden of showing harmlessness. [140][141][123][142][143]
The court rejected the argument that describing the defect as “jurisdictional” made certiorari automatic. It held that the term indicated an imperative legal obligation but did not remove the court's remedial discretion. [45][144][145]
The court also rejected the argument that receiving developer evidence amounted to the court conducting its own appropriate assessment. It held that the evidence could be used to determine whether the defect had made a material difference. [45][145][93][94]
In exercising discretion against certiorari, the court relied on the harmlessness of the error, the absence of demonstrated environmental harm, the public importance of renewable-energy infrastructure, the disproportionate impact of quashing on the developer, the delay in progressing the project, and the availability of declaratory relief as a more proportionate response. [30][146][147][148][149][150][151][152]
As to conservation measures, the court held that the applicants had not established any defect. Evidence showed that measures were in place, and the applicants had neither properly pleaded nor evidenced why they were inadequate. Arguments that existing measures were legally defective because objectives were absent were unpleaded and were not considered. [56][153][98][79]
The court declined to refer a question to the CJEU. It held that the proposed issue concerned the application of established principles, fell within the court's existing legal framework, and was not supported by authority creating genuine doubt. [34][154][35][115][37][155][156][157]
The court considered declaratory relief separately. It found a specific legal error, refused certiorari, and concluded that the unusual circumstances created sufficient public benefit in formally recording the error. [33][158][159][160][161][162][163]
Holding and Implications
Certiorari refused; declaratory relief granted. The proceedings were dismissed in their entirety except for declarations concerning the absence of site-specific conservation objectives and the resulting error in conducting the appropriate assessment. [164][165][166][167][168][169]
The court declared that the State respondents had failed to put in place the relevant objectives for the Kingfisher and Freshwater Pearl Mussel within the specified periods, and that the decision-maker contravened the Habitats Directive and transposing legislation by conducting an appropriate assessment without them. [166]
The planning permission was not quashed because the court found the error harmless, with no demonstrated environmental consequence or reasonable possibility that the decision would have been different. No new general precedent was stated; the decision applied established principles of discretion and harmless error to the facts of the case. [170][171][166][169]
The applicants were awarded limited costs relating to the declaratory relief, while there was otherwise no order as to costs. [172][173][174][175]