Key Points:

The venue was a chapel. The hosts were the peace-loving Green Party. But that did not stop Mayor Dick Hubbard and former mayor John Banks going hammer and tongs at the latest mayoral debate last night.

Mr Banks, who leads Mr Hubbard by 8.5 points in the latest Herald-DigiPoll survey, used the latest mayoral free-for-all to niggle the incumbent on vulnerable topics such as Queen St and water, and to dismiss the council's goal of making Auckland a carbon neutral city by 2020 as laughable.

"[Queen St] is the most expensive Chinese tiling job ever undertaken in a modern city in the world. It has a blowout of at least $20 million.

"It is a very, very bad joke and it is not going to be that good when it is finished," Mr Banks told the 60 or so mostly Green supporters at the Methodist Mission's Aotea Chapel in Queen St.

"Queen St is a shameful legacy of this particular council."

Mr Hubbard hit back, saying Mr Banks allowed cheap, nasty chicken coop apartments during his term.

"I'm building a high-quality Queen St and I'm proud of it. It's important we have a high-quality Queen St and what John is talking about, a project out of control, is complete and utter rubbish.

"We have the total endorsement of the Property Council and total endorsement of the retailers and they are paying for it voluntarily out of a targeted rate."

A question on having Queen St for pedestrians only drew a favourable response from many of the 11 mayoral candidates quizzed on how they might address environmental and social justice issues.

Mayoral candidate and Heart of the City chief executive Alex Swney favoured creating a mall in Queen St, but in stages, and spoke of his initiatives to provide free electric hybrid buses and cycle cabs in the central city.

Businessman Steve Crow wanted to close Queen St to all traffic, except electric trams running from Quay St and up Queen St to Karangahape Rd.

It would also improve inner-city security, he said.

John Hinchcliff and Coralie van Camp said the central city configuration would make it impractical to block Queen St off from traffic.

Lisa Prager said the $43.5 million upgrade was bureaucratic madness, while Raymond Presland said Queen St was a disgrace and the upgrade had taken too long.

Elaine West said the council needed to reclaim streets for pedestrians, not just Queen St, while Communist League candidate Felicity Coggan said working people appreciated improvements in public areas.

Scruff Ralph made the briefest speech of the night, saying he did not need the $158,000 mayoral salary and would give $100,000 to the City Mission and Women's Refuge.