A majority in both the lower and upper houses of federal parliament support Australia becoming a republic, the republican movement has claimed.

The Australian Republican Movement is backed by Malcolm Turnbull, and it claims the support of other senior government figures including deputy Liberal leader Julie Bishop, and moderates in cabinet Christopher Pyne, Marise Payne and Simon Birmingham.

Even leading younger conservative figures Josh Frydenberg and George Christensen support a republic, although the latter says his support is “subject to the right model being chosen” including a series of significant and ambitious constitutional changes.

In all, 81 members of the House of Representatives, and 40 members of the Senate have declared their support for an Australian republic, the movement says.

According to ARM the number may be even higher as 58 lower house MPs have not stated a position on the republic. Eleven lower house MPs are committed monarchists.

In the upper house, 21 senators were undeclared or undecided and 15 favour the monarchy.

ARM hopes the figures will help persuade Turnbull to take the lead on amending the constitution to install an Australian head of state.

Turnbull unsuccessfully led the “yes” campaign in the failed republic referendum in 1999. After becoming prime minister in September 2015, Turnbull said that there will be no move to become a republic until Queen Elizabeth is no longer on the throne.

Turnbull is due to speak at the republican movement’s 25th anniversary speech on Saturday.

Peter FitzSimons, chairman of the ARM, said Turnbull “has a unique chance to put the republican cause firmly back at the centre of the national agenda”.

“The majority of the public want it. Every premier and chief minister wants it. Now it turns out that our federal representatives agree as well.”

The Labor leader Bill Shorten has called for Turnbull to join him and work to make new progress to an Australian republic. Labor’s policy is for a republic.

According to ARM’s figures, the Greens are the most pro-republic, with 100% in support, followed by Labor (93%). Just 19 Coalition parliamentarians are openly in support of a republic (17%) although most, 65, are undecided or undeclared.

If Labor MPs are bound to support the republic, support climbs to 86 in the lower house and 42 in the Senate.

George Christensen, chief whip of the Nationals, said: “A renewed push for an Australian republic gives hope ... of having someone who is Australian and not subject to any foreign power as our head of state.”

He said it also gave hope that “we can reform government to make it more representative and responsive to the needs and desires of the Australian people”.

Echoing the debates around the 1999 referendum, Christensen would favour a directly elected head of state.

“I support a republic controlled by the people with a distinct separation of powers between the head of state and the legislative arm to provide the right checks and balances,” he said.

“That clear separation of powers might be achieved by doing away with the notion of a prime minister.

“Instead the head of government power currently held by the prime minister would go to the head of state, which we could either call President or retain the title Governor General.”

Christensen is also in favour of four-year fixed terms, similar some state governments.

