The High Court has quashed a Bord Pleanála decision to grant planning permission for more than 200 homes in Blackrock, Co Dublin.

Southwood Park Residents Association challenged the board’s permission last February for the Cairn Homes development on 7.9 acres on the grounds of Chesterfield House, a protected structure, on Cross Avenue.

The application, because it was for a strategic housing development, was dealt with under fast track legislation which allows builders to bypass the normal local authority planning process and go straight to An Bord Pleanála for permission.

The only way to challenge it was by way of judicial review in the High Court which began on Tuesday.

On Wednesday, Mr Justice Garrett Simons, in a preliminary ruling, said the failure of the developer to include in its online planning documents information relating to the potential impact of the development on various species of bat, which are protected under EU law, was fatal to the validity of the permission. An earlier version of the document was posted online in error.

This appeared to have happened due to inadvertence and none of the parties were aware of it until the action began this week, he said.

While Cairn Homes conceded that, as that regulations requirement had not been fulfilled, it said the permission should be set aside on that narrow ground.

Rather surprisingly, the judge said, An Bord Pleanála argued the breach was of a minor, or “de minimis”, nature and did not affect the validity of its decision to grant permission.

He said the regulations “could not be clearer in their terms” and the failure to post the correct version online represented a breach of those regulations. The board’s reliance on case law in relation to “de minimis” breaches was misplaced, he said.

It “cannot be characterised as trivial, technical or insubstantial”, he said.

The effect of it was that it undermined undermined public participation in the planning process and distorted the interpretation of the planning permission itself, he said.

The judge quashed the decision after he was told by Eamon Galligan SC, for Cairn, that a new planning application would be submitted.

He awarded costs against the board saying this was a case which should have been compromised once the breach was discovered.