THE Greens today told Prime Minister Malcolm Turnbull he could put them out of business by making “genuine changes” on issues such as climate change.

The offer came from Greens leader Richard Di Natale, who offered to quit politics if Mr Turnbull altered direction on climate policy, same-sex marriage and the treatment of refugees.

“If it represents a genuine change in direction and we finally get back on track when it comes to those issues, terrific,” Senator Di Natale told the National Press Club.

“I’ll go back and grow some vegies … But I’m not holding my breath.”

Senator Di Natale is the least scary to mainstream voters of the three most recent Greens leaders, but today he firmly stated a minimum price for Green support in the upper house.

And, as a warning, he outlined what might happen if the Greens did not see the changes they wanted.

Senator Di Natale told the Press Club that former Labor prime minister Julia Gillard did not deliver on the three policy areas, “and the Greens had their most successful (election) result ever”.

He pledged to co-operate where possible and indicated the Greens would give critical backing to measures ending the “gaming” and “preference harvesting” that results in independents reaching the Senate on minuscule primary votes.

The Coalition wants backing in its bid to reduce the leverage of senators not from major parties.

But Senator Di Natale warned the Greens would use their own leverage in the Senate as a check on government actions, saying voters wanted it.

“The best friend that Tony Abbott ever had was the Senate because if those measures in that first [2014] Budget were passed, he wouldn’t have made it past year one, let alone year two,” he said.

“So Malcolm Turnbull has an opportunity to work with this Senate, with us the Greens, if it means getting progress on some of those key issues.

“Where the ideas come from is much less important than whether they are good ideas and whether we can get the Parliament to support them.”

Senator Di Natale said he liked the diversity of the Senate provided by the eight crossbench senators, who sit alongside the Liberals, Nationals, Labor and the Greens.

“But I’m also a democrat and if you are in the Parliament you really should be elected there democratically. People should have to vote for you to be in there. Otherwise we might need to reinvent the whole business,” he said.

“The fact is that we have people elected on half a per cent of the [primary] vote, other people not elected on 10 per cent of the vote.

“Worse than that is your vote might be given to the anti-climate change party or candidate and it ends up with the pro-climate change party or candidate. That’s not democratic.”

Liberal Democrat David Leyonhjelm rejected pressure for major changes to the voting system and said the Greens themselves had been beneficiaries.

“The system has not been any different since 1985. It was the same system that led to [first Greens leader] Bob Brown being elected for the first time in Tasmania,” he told Sky News.

“He wouldn’t have been elected if we’d had the optional preferential voting above the line, which is what the Greens favour.”