New Greens leader Richard di Natale has given the government cause for optimism on the eve of its second budget by opening the door to supporting the indexation of petrol excise.

He has given Labor cause for concern by declaring the Greens should be a party for the progressive mainstream and intended to lift its vote to 20 per cent nationally.

The 44-year-old Victorian senator, former doctor and accomplished AFL player who entered Parliament after the 2010 election, declared himself to be “no ideologue” after he emerged as the party’s third federal leader following the shock resignation of Christine Milne on Wednesday.

Senator Milne, 62, said after 25 years in state and federal politics she had decided to not contest the next federal election and it was appropriate she stand down to enable her Tasmanian branch to preselect a replacement.

Her resignation, which was as much of a shock as that of her predecessor Bob Brown three years ago, caught some of her colleagues unaware.

Deputy leader Adam Bandt, who had been tipped as a future leader, did not recontest his position and was replaced by a new joint deputy team of Larissa Waters and Scott Ludlam.

He is understood to be unhappy at what some in the party were claiming was an ambush.

Senator Milne has kept the Greens’ vote at about 12 per cent nationally since she took over as federal leader and, at the 2013 election, the party secured a record 10 Senate spots, giving it the balance of power in its own right.

Her critics claimed she was too ideological and was happy to confine the Greens to a protest party rather than use its balance of power.

The government had long been frustrated that she opposed the decision to reintroduce  fuel excise indexation in last year’s budget, despite it being Greens policy.

The measure, worth $2.2 billion over four years, but much more beyond that, has been enacted by regulation but must be enshrined by legislation by September or it will lapse.

Senator di Natale said the Greens under his leadership would look again at the petrol decision.

“We’ll look at everything, we’ll have a discussion,” he said.

He said his basic philosophy was decent government which looked after people, provided access to quality healthcare and education and looked after the environment.

“I’m not an ideologue,” he said.

“In some areas you might be surprised by what I’ve got to say, in other areas it’ll be entirely predictable.”

Senator di Natale threw down the challenge to Labor, which has already been eroded from the left by the Greens, by declaring he wanted to increase the party’s share of the national vote.

“We are the natural home of progressive, mainstream Australian voters,” he said.

Labor leader Bill Shorten shot back: “Labor believes in a strong economy that doesn’t leave people behind,” he said. “Labor’s priority is to protect living standards, jobs and a secure economic future. The Greens have other priorities.

“I’m proud to lead the only political party that gives its members their say in choosing their leader.”

When news broke of Senator Milne’s resignation, Treasurer Joe Hockey’s immediate reaction was to “hope the Greens see common sense” and reverse opposition to fuel excise indexation.

Government Senate leader Eric Abetz paid tribute to Senator Milne’s life of public service, wished her well and  noted she was the only woman to lead a party at state and federal level.

“Having said that, as leader of the government in the Senate, I hope that the Greens will take this opportunity with a new leader to reassess their continual opposition in the Senate to government legislation and economic reform,” he said.

Extracted in full from Australian Financial Review.