The High Court has begun hearing a challenge to permission for a long-stalled €10 million Supermac’s motorway plaza in Co Clare.

Representing himself in the action, engineer Michael Duffy is asking the court to overturn An Bord Pleanála’s 2022 decision to approve Pat McDonagh’s plan for the development off the M18, at Kilbreckan, Doora, outside Ennis.

Mr McDonagh, who is founder and owner of the fast-food chain, first lodged plans for the plaza a decade ago. An Bord Pleanála denied him planning in 2016 before he secured a grant from Clare County Council in December 2020, which the board upheld in October 2022.

Mr Duffy, from Kilfenora, Co Clare, alleges there were flaws in the board’s Appropriate Assessment, which screens for a project’s potential harmful effects on special areas of conservation.

On Tuesday he also submitted that the board should not have taken “verbatim” Irish Water’s assessment of the capacity of the nearby Clareabbey wastewater treatment plant. He said the board could take the agency’s view into consideration but “had a duty to look beyond that”.

He said he had raised concerns about the facility’s capacity in his objection to Mr McDonagh’s planning application, while the Environmental Protection Agency reported it was overloaded in 2018.

An Bord Pleanála, as the respondent decision-maker, and Mr McDonagh, who is a notice party, are contesting the case and deny his claims. Mr McDonagh was present in court for the first day of the hearing.

Clare County Council is also a notice party but is not participating in the case, the court heard.

The board maintains its appropriate assessment and decision are not flawed and should stand. It also takes issue with how Mr Duffy has pleaded his claim.

Mr McDonagh’s legal team argues, among other points, that Mr Duffy’s complaints are premised on a selective and incorrect reading of An Bord Pleanála documents.

The High Court gave Mr Duffy permission last July to proceed with his action, but on narrower grounds than he wanted. Mr McDonagh’s lawyers had asked the court to preclude Mr Duffy from advancing to a full hearing.

The case before Mr Justice David Holland continues on Wednesday.