Real Republic Australia's David Muir said the royal family had repeatedly acknowledged that the republic debate was one for Australians to have and make a decision about the future of the nation.

Support appears to be waning, with just one in three people responding to a Nine Entertainment poll in favour of replacing the monarchy with an Australian head of state.

Mr Muir said the royals would be open to a debate.

"Members of the royal family from the Queen down and certainly Prince Philip have taken the common-sense view that the republic debate is not a reflection on them," he said.

"They have on many occasions stated quite clearly that they view the issue as one for Australians to settle and that they will abide by our decision."

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Mr Muir said the late Duke of Edinburgh had been relaxed about the prospect of an Australian republic for decades.

"Even back in the 1980s he acknowledged that if Australians wanted to become a republic then the royal family would accept the decision," Mr Muir said.

"The Queen was also reportedly quite relaxed about a republic when former prime minister Paul Keating briefed her back in 1993 about his blueprint for the republic debate."

Mr Muir said it was not disrespectful to the British royal family if Australians conducted a republic debate.

"In fact we should already have started it long ago, but there has not been the political will or leadership since Keating for having the discussion," Mr Muir said.

"Even Malcolm Turnbull, a staunch republican, didn't lift a finger to initiate the debate. He preferred the cop-out of waiting until the Queen's reign ends.

"The debate should never be about criticising or belittling the royal family in any way. But by deferring debate Turnbull and others are laying the groundwork for a negative get Charles exercise and that's the last thing we want.

"Senior royals would be quite comfortable with a republic debate and, quite frankly, the sooner it starts the better."