Australia’s gun lobby spent more per capita on political donations in one year than America’s National Rifle Association did in 2018, a report has found.

In the wake of revelations that One Nation sought millions in donations from the NRA, the report from the Australia Institute has found Australia’s gun lobby spends just as much, and has as many members as the NRA, when adjusted for Australia’s smaller population.

On Tuesday the interim leader of the NSW Labor party, Penny Sharpe, said she would support a ban on donations from the firearms lobby in the state, which already bans political donations from the property development, alcohol and gambling industries.

In the 2015-16 financial year, the Shooting Industry Foundation of Australia donated $64,000 to political parties, which equates to $2.56 spent per thousand Australians.

This was more than the NRA spent in 2018, which was US$2.51 per thousand Americans (US$823,842 total).

Various Australian gun groups donated $1.7m to political parties since 2011, with Bob Katter’s Australia Party receiving the most ($808,000).

The Shooters’ Party received $699,000, the Liberal Party $46,000, the Liberal Democrats $37,000, the Nationals $36,000, the Labor party $33,000 and the Country Alliance $30,000 over the same period.

The report, commissioned by Gun Control Australia and Getup!, noted that this was based only on publicly-available records, and there could be more spending undisclosed. Australia’s gun groups also spent similar amounts to the NRA on campaign spending, which is distinct from direct political donations.

In 2017, Australian gun lobby groups spent more than $500,000 running a campaign in the Queensland state election.

Combined with a campaign during the 2017 Victorian state elections, the SIFA spent the equivalent of $30.12 per every thousand Australians, more than the NRA’s 2018 campaign spend of US$28.10 in 2018.

Another group, the Sporting Shooters’ Association of Australia, has 200,000 members, which is 0.8% of the Australian population. The report compared this to the NRA’s 4 million members, which is 1.2% of the American population.

The author, Bill Browne, wrote that “there is a real danger of our firearm laws being watered down” because Australian’s don’t realise the scale and power of our own gun lobbies.

“Australians are probably more familiar with the NRA than Australia’s equivalents,” he wrote. “[But] firearms interest groups have made a concerted effort to undermine these laws and loosen state-level gun controls.”

Sharpe, who took over as interim Labor leader in NSW after Michael Daley stood aside, told Guardian Australia she would support an extension of the existing bans on developers and the liquor and gaming industries to include gun groups.

“Gun laws in Australia cannot and must not be watered down,” she said. “Donations should play no role in any attempt to do so. I would support a ban.”

On Tuesday an al-Jazeera investigation revealed senior One Nation figures James Ashby and Steve Dickson had sought millions in donations from the NRA during a trip to the US last year in a bid to seize the balance of power and weaken Australia’s gun laws.

The report prompted an immediate backlash in Australia and placed increased pressure on the prime minister, Scott Morrison, to rule out preference deals with the far-right party at the May federal election.

In a text message on Tuesday, Ashby told Guardian Australia that “no money was ever received or offered” from either the NRA or Koch Industries.

At a news conference alongside Dickson later in the day, the two men said they had travelled to the US to learn about the NRA’s campaigning tactics and had only discussed donations in the context of a drinking session.

“I will be the first to admit, we’d arrived in America, we got on the sauce, we’d had a few drinks and that’s where those discussions took place,” Ashby said.

One Nation is one of several rightwing parties to have received thousands of dollars in donations from the Australian gun lobby in recent years as part of a push to pursue changes to firearm laws established after the Port Arthur massacre in 1996.

In the past decade, pro-gun groups have been able to use ballooning membership numbers – ironically won as an unintended consequence of John Howard’s changes after Port Arthur – to flex their political muscles.

In NSW, developers and the liquor and gaming industry are all banned from donating to political parties but pro-gun groups have continued to pour money into the state.

The Shooters Fishers and Farmers party received more than $35,000 in donations from gun groups before Saturday’s NSW state election, helping the party secure three seats in the state’s lower house, as well as its two upper-house members.

At Saturday’s state election, the Coalition managed to hold on to a wafer-thin majority but the premier, Gladys Berejiklian, has said she wants to work closely with the three independent crossbench MPs in the parliament.

One of those, Joe McGirr, said he would also support a ban on firearm lobbyists, saying he believed interest groups had too much sway in the political process.

“I think that having donations from these pressure groups is actually a problem,” he said. “It really does undermine democracy. I think Australians have a view that everyone should have a fair go and I think that when people with money can get unfair access it undermines that. That’s really what we’re talking about.”

The al-Jazeera investigation used hidden cameras and a journalist posing as a grassroots gun campaigner to expose the far-right party’s extraordinary efforts to secure funding in Washington DC in September.

The investigation also recorded a meeting between the One Nation officials and representatives from Koch Industries, which funds various conservative causes in the US.