A rogue Liberal MP has criticised the NSW government’s koala policy as “sheer madness” but the premier says the coalition has done “more to protect koalas than any government before us”.

Outgoing Liberal MLC Catherine Cusack told parliament’s upper house on Wednesday the government’s koala policy is accelerating the destruction of their habitat.

She also says the former environment minister and now Treasurer Matt Kean told her he was “one of the greatest—probably the greatest—environment ministers in Australian history”.

Ms Cusack posted a series of screenshots of text messages on Twitter this week showing former premier Gladys Berejiklian urging her to support the policy during the coalition’s “koala wars” in 2020.

Premier Dominic Perrottet defended Mr Kean’s record, saying the state was leading the country on the environment.

“In an area where the Liberals and Nationals are not seen to be leaders when it comes to the environment, I think … our state, is by far the best in the country,” he said on Thursday

“A lot of that is testament to these policies and of minister Kean. We’ve done more to protect koalas than any government before us.”

The government spent four years developing its koala State Environmental Planning Policy  (SEPP) and while trying to pass the legislation endured a bruising stoush that threatened to destroy the Liberal-National coalition.

The policy was defeated after Ms Cusack crossed the floor, saying the policy “has zero to do with protecting koalas”.

A deal had been done between the Liberals and Nationals to ensure the policy would pass, she told the upper house on Wednesday night.

“The NSW Koala Strategy is based on the idea that we can buy our way out of the problems created by private native forestry, native forest and native vegetation clearing — which is accelerating destruction by a factor of three,” Ms Cusack said.

“The plan sees volunteers and wildlife funds planting and revegetating areas for the future, while across the road established trees that are being used by koalas are being cut down—and it is subsidised by taxpayers.

“This is sheer madness.”

Ms Cusack made the comments while supporting the Greens Great Koala Protected Area Bill.

Greens MP Cate Faehrmann lamented the defeat of the bill on Wednesday night.

“Unfortunately Labor voted with the government to stop the creation of the Great Koala National Park,” she said.

Mr Kean says Ms Cusack’s claims of a deal are “absolutely untrue”.

“Everyone knows that I fought to protect koalas,” he said on Wednesday, citing the $193 million funding package for the endangered species he secured while environment minister.

“I think it’s a matter of public record that my relationship with (former NSW Nationals Leader) John Barilaro nearly broke the government over the stance I took to protect koalas.”