Justice Tim Moore of the Land and Environment Court ruled last week the delegates who had considered the proposed mergers of North Sydney, Willoughby and Mosman councils, as well as Strathfield, Burwood and Canada Bay, had failed to consider one and two aspects respectively among those required by the Local Government Act.

On that basis, Justice Moore ruled the proposed mergers could not go ahead.

In contrast, he found no flaws in reports prepared into a proposed merger affecting Hunters Hill, Lane Cove and Ryde Council, while there was also no basis to oppose a merger between Ku-ring-gai and Hornsby councils.

The mayor of Mosman, Peter Abelson, said the council's view was that the delegate who prepared the report into the proposed merger, Ian Reynolds, would have to review the entire report into an amalgamated council, and not just the one element Justice Moore said was deficient.

"He has to take into account any information that has arisen since he wrote his first report in mid-April," Cr Abelson said.

"He can't simply rewrite a few paragraphs and say he's done it," he said.

Mosman Council wrote to Mr Reynolds as well as Minister for Local Government Paul Toole last week setting out its position. A spokeswoman for Strathfield Council said that council had a similar view to Mosman's.

Mr Toole, meanwhile, has not spelled out how the government plans to deal with the identified deficiencies in the Strathfield and Mosman merger reports.

A spokesman for Mr Toole said: "The government is closely examining the findings in relation to the delegates' report."

Should the government have to rerun the public inquiries into potential mergers of affected councils, it would be likely to drag out the process of amalgamations for many months yet.