When Richard Di Natale embarks on one of his first overseas trips as leader of the Australian Greens, it will be for a cause that is close to his heart but has nothing to do with climate or the environment.

“I’m going to Portugal in July to look at what they are doing around the treatment of drugs,” he tells The Saturday Paper. “They have made a decision that, rather than prosecuting people who use drugs, they have mandated treatment, they have a whole lot of housing and social services directed at them.”

“I’m generally inclined to more transparency than less; that’s my default position.”

It is perhaps an unusual priority for a Greens leader, at a time when multiple international climate change events are taking place in the lead-up to global talks in December. It will be his first major overseas trip after visiting New Zealand in June for an international Greens conference.

But Di Natale is an unusual Greens leader. He’s only the third leader of the party since it formed in 1992. The others, Bob Brown and Christine Milne, were both environmentalists whose political beliefs were forged in wilderness crusades. Di Natale wants to broaden the party, claiming it is the natural home for “mainstream progressives”.

The change of leadership in the Greens to this little-known former GP, who insists he is more interested in outcomes than ideology, may have opened up opportunities for the government to negotiate senate passage of legislation. But it also presents challenges for Labor. With Di Natale in charge, the Greens will no doubt become more vocal on health policy, an area that Labor considers among its core strengths.

First, though, he has internal issues to resolve.

Within hours of assuming the leadership on May 6, Di Natale was under fire from some of his own members for how he won the top job. His swift ascent to replace Milne angered some within his party room, who suspected the outcome had been rigged and resented the lack of time for other possible candidates to canvass support.

Initially, he was dismissive. “Surprise, surprise, that’s politics,” he said in his first press conference. But now he admits to The Saturday Paper that the change could have been handled better and with greater transparency.

“One of the first things I did was talk about the leadership process,” he says. “We’re looking at the party room rules.”

It has always been one of the ironies of the Greens. As a party, they supposedly stand for transparency and accountability, challenging big business and established power structures, yet their own internal processes have been as open and transparent as a meeting of the Freemasons.

The switch from Brown to Milne in 2012 was even more secretive, occurring within one party room meeting and announced as a fait accompli. This time, it was over in a matter of hours.

“With Bob there was a precedent set, if you like,” says Di Natale. “We followed that precedent the second time. We’re now looking at whether we can do things a bit better, maybe allow more time.”

It’s not the only process he’s changing in the party. Significantly, Di Natale has decided to open a conversation with the press gallery about the Greens’ internal deliberations. He has decided it’s time for the party, with 10 senators and one MP, to be more open about how it works, to let some of the nuance of its internal debates be aired publicly.

Each week when parliament sits, the Coalition and Labor hold background briefings for reporters about issues that have been discussed in their respective party room meetings. Sometimes these sessions are informative, sometimes they are farcical in their creative spinning of events or omission of damaging detail, but they do provide an officially sanctioned version of the parties’ internal discussions. Reporters can then glean a fuller and more accurate account from their sources.

The Greens’ internal processes have been largely unknown and, to an extent, unknowable, as there was no official briefing process and a surprising level of party discipline. Under Brown and Milne, there was a façade of complete unity that verged on groupthink. Leaks occurred occasionally but were uncommon. The emphasis on unity is understandable in a party that wants to avoid at all costs the sort of public infighting that contributed to the disintegration of the Australian Democrats. Such discipline is easier to enforce in a small party room.

Now Di Natale has signalled a relaxation of this discipline, saying colleagues need not toe a party line but are welcome to voice their own opinions publicly. Party room briefings will also be held, in line with other established parties.

“I’m very relaxed about people expressing their views which occasionally might be different from where most people in the party room sit,” he says.

He also wants a discussion within the Greens National Council about whether more sessions of the party’s conferences should be open to the media. “I’m generally inclined to more transparency than less; that’s my default position,” he says, but adds that there are good arguments for keeping some conference sessions closed in the interests of allowing frank and open debate.

At the first Greens party room briefing on Monday, reporters learnt that the leadership change had resulted in a minor reshuffle of portfolios but a bigger rejig would be postponed until after the election. Key staffing appointments were also revealed, including that former NSW upper house member Cate Faehrmann would be Di Natale’s chief of staff and Colin Jacobs his chief policy adviser.

There were also insights into the party’s unique “consensus-based decision-making”.

Votes are rare within the Greens party room. Di Natale concedes it would sometimes be quicker to vote on an issue but says the consensus-based approach allows all views to be aired and for participants to then arrive at a decision they can all support.

One of the reasons he instigated the briefings was he felt that some of the party’s decisions had been misrepresented. For instance, there were reports last year of divisions and tensions over the decision to oppose the fuel tax increase after last year’s budget.

“It was a tough call,” he says, but he says the party room supported the fuel tax decision, which some external critics argued was inconsistent with the Greens’ support for a pollution tax.

Now he is again talking with the government about the fuel tax increase, which needs to be passed by October. Otherwise, tax collected thus far, since the government circumvented the senate and used administrative process to increase it, will need to be refunded to petrol companies.

Di Natale argues some of the funds raised would need to be spent on public transport, but says he is “realistic enough” to understand the government will want to pocket some of the revenue as savings. He met Tony Abbott in budget week to discuss fuel tax, among other things, and saw Treasurer Joe Hockey on Wednesday.

“We wouldn’t support it unless they were prepared to negotiate,” he says. “There appears to be an appetite to negotiate. Conversations were constructive.”

It’s still early days, but that’s a far cry from how Milne characterised her dealings with the Abbott government.

When asked if he trusts Abbott, the pause lasts almost three seconds. “That’s a good question,” he says eventually. “I mean, clearly he’s broken faith with the electorate … so that has to tell you something. My default position will be to give somebody an opportunity to demonstrate they can be trusted and the moment they break that trust, then you know the terms on which you will be operating.”

He struggles to name any Coalition frontbenchers he respects, eventually nominating Liberal senator and assistant minister for education and training Simon Birmingham as a “decent person”.

As leader, Di Natale has chosen to retain the health portfolio, as well as responsibility for two of his other passions, multiculturalism and sport.

Di Natale came to the party through his interest in public health policy, and his time as a doctor shaped his outlook. Working in a drug and alcohol clinic in Geelong, prescribing methadone to addicts, he saw things that led him to believe there should be no criminal penalties for possessing illegal drugs for personal use. “It’s not effective as a deterrent,” he says.

His visit to Portugal in July to observe drug medicalisation will be privately funded, at the end of a family trip to Britain. “I have seen the impact of substance abuse on people,” he says. “I don’t come at this from some libertarian perspective that everybody should be able to do what they want, when they want.”

He argues that the Greens’ drugs policy, which has occasionally been pilloried as radical, is in fact in tune with community views, as most parents would prefer that, if their offspring developed a drug problem, they were helped rather than imprisoned.

In this parliament, the Greens have outlined policies to slash the diesel fuel rebate to mining companies and to save $10 billion over four years by reducing superannuation tax concessions to those earning more than $100,000. Di Natale says he is also “actively looking at negative gearing”.

Yet there are still proposals in the Greens’ platform that seem more like fantasies than mainstream policies. For instance, offering free university education and living allowances for students would cost many billions of dollars.

Asked whether this is a responsible proposal, Di Natale says: “It’s a question of priorities ... Is it responsible to give $10 billion of rebates to miners? Is it responsible to have superannuation become a vehicle for high-income earners to minimise tax? Is it responsible to allow a tax break for people to buy properties when first-home owners can’t afford to buy? I think the goal is a good one.”

Labor frontbencher Anthony Albanese, whose federal seat of Grayndler in Sydney includes the Greens-held state seat of Newtown, is scathing about the Greens and Di Natale’s claims they are the party of “mainstream progressives”.

“When you look at the details of their policies, they are in many cases undergraduate, unsophisticated and have no resemblance to having a mainstream economic policy that is fundamental if you want to create the space to have good social and environmental policy,” says Albanese. “The Greens spend most of their energy targeting progressives in the Labor Party, rather than trying to convince people out there in a broader sense about progressive views. Their end objective, stated by themselves, is to win seats that are currently held by progressives, which will simply result in a more conservative Labor Party and an inability to change things.”

There is a view in some parts of the Labor Party that, if demographic changes continue in some inner-city seats such as Albanese’s or the seat of Melbourne, now held by the Greens’ Adam Bandt, then Labor will eventually have to abandon them as Greens enclaves.

Just as Albanese challenges the claim the Greens can be considered “mainstream”, Di Natale says some views represented within the Labor Party are hardly “progressive”.

“Hearing Labor senators get up and make speeches attacking gay marriage, abortion, dying with dignity – they’re not progressive views,” says Di Natale. “I’m talking about progressive mainstream, which is obviously a smaller group.”

Although in his first press conference as leader he bluntly stated his goal was to win more seats in both houses, he puts it more altruistically in our conversation.

“I want to give a voice to a whole lot of issues I care about … If that translates to a growing voter base for us, that’s great. If that comes off the Labor Party or the Coalition, so be it. If the Coalition or Labor are so threatened by it they change their policies and our vote shrinks, that’s still a good outcome.”

Needless to say, he’s not Bob Brown and nor does he speak on climate policy with the same authority or zeal as Milne. His challenge will be to raise his profile by the next election. It will help that he is a good communicator, speaking with a no-nonsense pragmatism and exuding the trustworthiness and patience of a good doctor: attributes that can count for a lot in an electoral contest.

He claims he doesn’t spend a lot of time thinking about the Labor Party, but the futures of the two parties are inextricably linked. Any electoral gains for the Greens are likely to come at the expense of Labor and could force it to again rely on support from the smaller party to govern.

Unlike his hesitation over whether he respects Abbott, Di Natale answers immediately, emphatically and in the affirmative when asked if the Greens would again support Labor to form government. “Of course,” he says. “Part of the business of being here is to do things and see change.”

For the moment, though, that’s still hypothetical.