David Benson-Pope.

The Dunedin City Council got it wrong when it voted - without debate - to pull its support for a unitary council investigation.

Now it is having another go.

It emerged yesterday the motion tabled by Cr David Benson-Pope at a council meeting earlier this month did not comply with the council's standing orders.

The motion, to rescind councillors' earlier support for investigating a possible merger of the city council and Otago Regional Council, needed to have the signed support of one-third of councillors before being considered.

It did not, and nor did the move satisfy a requirement for "sufficient information to satisfy the decision-making provisions" under the Local Government Act, a report by council chief executive Sue Bidrose said.

The errors were identified only after councillors had voted to pull their support for the investigation, helped by Cr Kate Wilson, who used a "closure motion" to prevent debate on the move.

Dr Bidrose had since sought legal advice on the situation, which confirmed the outcome of the April 30 vote needed to be revoked, or the council could face a legal challenge.

As a result, councillors would again consider the matter - and a new motion from Cr Benson-Pope that complied with standing orders - at next week's council meeting.

The notice of motion was signed by Mayor Dave Cull and eight city councillors, suggesting it was again likely to be approved.

Cr Lee Vandervis did not respond to requests for comment yesterday, but Mr Cull put the mistaken process down to changes in standing orders, which meant "we're not all completely up to speed".

He predicted the same outcome, but, asked if he expected Cr Wilson to use her closure motion again, said: "I hope not."

Cr Wilson said she would not do so.

"I don't think it would work a second time. I think it worked last time because no-one knew about it."