"In my years in office I often found that consultation with iwi was flawed – invariably rushed and superficial, often telling people what is going to happen rather than actually consult them."
The Kermadecs are about 1000km north of New Zealand.
In September 2015, Prime Minister John Key announced at the United Nations a plan to establish a 620,000km sq marine reserve covering the 200 nautical mile Exclusive Economic Zone.
The bill setting up the sanctuary extinguishes without compensation the fishing rights of Te Ohu Kaimoana (TOKM), the Māori fisheries commission, the body responsible for administering the assets of the 1992 Māori fisheries settlement.
It was put on ice after the Māori Party threatened to withdraw its support from the government and TOKM lodged action in the High Court.
Most of the preparatory work had been done by Environment Minister at the time Nick Smith in a truncated process, and officials' advice was used sparingly it is understood.
Finlayson does not directly criticise any colleagues in his speech but he said there was "inadequate consultation within government".
"Observing the very detailed cabinet process limits the opportunity for things to go wrong," he said.
"Interdepartmental discussion and discussion at officials' level followed by consideration by cabinet committee then cabinet will eliminate the issues to be highlighted and any red flags to be raised."
Finlayson retired from politics last year to return to the law, which gives him greater freedom to speak out against the actions of his own party in government.
He said in his speech that the integrity of the 1992 fisheries settlement had to safeguarded at all costs.
"We have done great work as a nation over the last 30 years to address the historic grievances of Māori.
"It was clearly understood that these settlements must be full and final and, not subject to change every generation or so.
"That means they must be honoured by all parties.
"It is the risk of settlement being undermined that greatly troubles me. I don't want this important intergenerational work to founder."
He said any solution to the Kermadecs had to be based on ecology not ideology.
"In today's world, there is an increasing danger of facts being less important than ideology. It is a very dangerous phenomenon and needs to be challenged whatever the issue."
The Quote Management System worked because it was founded on evidence based sustainability.
The best way of addressing stock depletion was to do something about the flotilla of tuna fishing boats, mainly based in America Samoa, which stayed around the northern end of the Kermadecs.
The United States needed to address that issue.
He also said if the sanctuary proposal went ahead, some fishing needed to be permitted.
"That is not an absurd proposition. It has been agreed to in Rapa Nui [Easter Island]."
Some fishing is also allowed in the Ross Sea Marine Protected Area.
He called for fresh discussions over the Kermadecs to begin, without anger or recrimination.
"Let's maintain the basic principles of the treaty relationship and the treaty-based agreements we have made. And this time, let's get it right."
Resolving the impasse around the Kermadec Sanctuary is mentioned in Labour's coalition agreement with New Zealand First and its confidence and supply agreement with the Greens.
