The controversial demolition of historic buildings on a Victorian mailboat pier in Dun Laoghaire by a semi-state company could contravene planning regulations, the local authority that sanctioned the works has admitted.

In early September, the Dun Laoghaire Harbour Company demolished a group of derelict buildings on the Carlisle pier in Dun Laoghaire without planning permission.

An Taisce have expressed "grave" concern that Dún Laoghaire Rathdown Council indicated to the harbour company at the time that they did not need planning permission to demolish the buildings and then allowed the firm to carry out the works.

The national trust maintains the harbour company should have sought permission to demolish the buildings because they are located within the area of the harbour itself, a protected structure.

Kathleen Holohan, head of the council's planning department, had stated that the demolition works constituted "exempt development" be­cause the pier fell outside the curtilage of those elements of the harbour, which are protected structures.

But in a letter to councillors last week, county manager Owen Keegan indicated that the local authority had significantly altered its opinion of the status of the works.

"The initial view of the planning authority was that the proposed works were exempt and did not require a grant of planning permission. This view was communicated, in good faith, to Dun Laoghaire Harbour Company," he said.

"However, on more detailed examination... the planning authority formed the view that there was, in fact, uncertainty in relation to the planning status of the works."

Contractors working on behalf of the council demolished several of the buildings on the pier last month.