The Government is wading into the turgid waters of fluoridation, with an “authoritative report” being developed behind the scenes to counter increasingly aggressive anti-fluoride campaigners.

A panel of some of the country’s top scientific experts in the field has been quietly working for months on the report – to be made public in the next few weeks – after pleas from councils besieged by a torrent of opposition to adding fluoride to drinking water.

At least three councils have been embroiled in legal battles in the past year, including the Kapiti Coast District Council.

The report is being fronted by the prime minister’s chief science adviser, Sir Peter Gluckman, and the Royal Society of New Zealand.

Anti-fluoridation group New Health NZ Inc yesterday accused the society of convening a “secret panel” to support its pro-fluoride views. “We are chiefly concerned that there has been no transparency around this process,” chairman David Sloan said.

But Gluckman – a strong supporter of fluoridation – said there was nothing secret about the report and its findings would be released after it was internationally peer-reviewed, like any other scientific paper. “It will be based on science, not opinion and bias.”

The panel, which had Prime Minister John Key’s approval, was convened after councils approached the Royal Society seeking guidance about the science on fluoridation, he said. “Councils are confused, and it is important that they have an expert panel to summarise the science.”

In 2012, the Royal Society declined to conduct an inquiry, saying there would be “no value” in expending resources when the evidence was clearly in fluoride’s favour. But yesterday society president Sir David Skegg said that decision had been revised given recent “controversies”.

“There has been this campaign against fluoridation that has raised questions in some people’s mind,” he said. “So we are going back to square one to review the evidence.”

Fluoridation supporters – who include the Ministry of Health, the World Health Organisation and many major professional health associations – say it is a cheap, safe and proven way to improve dental health, particularly for children. But opponents claim it is forced “mass medication”, which causes more harm than good.

Water fluoridation remains patchy throughout New Zealand. Within the Wellington region, parts of the Kapiti Coast and Petone remain free of added fluoride.

Attempts by councils to introduce fluoridation are increasingly being met by intense lobbying from opponents, and sometimes legal action. Last year, the Hamilton City Council voted to drop fluoride from its water supply, claiming it could be harmful, only to reintroduce it last month after a public backlash.

Councils caught up in the long-running disputes are now trying to abdicate responsibility for fluoridation, with a meeting of local authorities last month agreeing to lobby the next government to hand over the decision-making to district health boards.

Local Government New Zealand president Lawrence Yule, who is also mayor of Hastings, said that, with anti-fluoridation groups raising the pressure, councillors were being forced to make decisions beyond their expertise.

“We are not health experts, we just own the water pipes.”