Tony Abbott has challenged Labor leader Bill Shorten to prove he isn't a dual citizen by releasing documentary evidence from British authorities.
"I say to Bill Shorten show it or shut up," the former prime minister told reporters in Canberra on Monday as he brandished a letter from the British government showing he renounced UK citizenship in 1993.
"Because if you haven't got a letter, you are in exactly the same position that he is in and you should let him and you should let the Parliament get on with its job this week."
Barnaby Joyce is running unfazed into another parliamentary week insisting he has the right to be deputy prime minister while the High Court decides his fate.
Labor is expected to disrupt business in the lower house until the Nationals leader steps down from cabinet or the court makes its ruling.
But after a morning run around Parliament House on Monday, Mr Joyce argued the tactics aren't helping the opposition's standing with voters.
"(They) want us to get on with the main game," he told reporters.
"They're talking about power prices, they're talking about jobs."
Mr Joyce again asserted he would have stood down from his ministerial position if the government hadn't received strong advice from the solicitor-general.
"You hold office until such time as death or you resign or the High Court finds otherwise," he said.
"Now everyone says that. Nick Xenophon says that. I heard Pauline Hanson say that."
Asked whether he would be acting prime minister when Malcolm Turnbull heads to the Pacific Islands Forum in Samoa at the end of the week, Mr Joyce said: "That's how the game works. The PM always has that right."
Labor argues there's no way the Nationals leader should be acting prime minister while his eligibility is in doubt.
Cabinet minister Fiona Nash's eligibility to sit in parliament has been referred to the High Court because of her dual-citizenship.
It was revealed in August she held British citizenship which under the constitution disqualifies anyone from being elected to parliament.
Attorney-General George Brandis on Monday said the government's view was that Senator Nash was not ineligible to sit.
Crossbench senator Nick Xenophon has also been referred to the court following revelations he was a British citizen by descent.
