Deputy prime minister Barnaby Joyce was a New Zealander and Queensland senator Matt Canavan is Italian, the federal government has conceded in its submission on dual citizenship going to the High Court.

The fate of the Turnbull government hangs in the balance, with Joyce part of its one seat majority in the lower house, with the court due to hold an initial directions hearing this Thursday, with Attorney-general George Brandis hoping the matter will be considered on September 13 and 14.

The court will look at five cases, including two former Greens senators, Scott Ludlam and Larissa Waters, who were born overseas and resigned, along with One Nation senator Malcolm Roberts, Joyce and Canavan.

Two more cases, Nationals senator and minister Fiona Nash, and South Australian independent Nick Xenophon, are also expected to go before the court, but parliament needs to meet to refer them.

In the government’s submission to the High Court, solicitor-general Stephen Donaghue says Canavan and Joyce “are, or were, citizens of Italy and New Zealand respectively”.

Joyce renounced his Kiwi citizenship – his father was born in New Zealand – within days of discovering it last week, but section 44 of the Australian Constitution, says a person is ineligible to stand for election they are “a subject or a citizen or entitled to the rights or privileges of a subject or a citizen of a foreign power”.

And the attorney-general’s plan to expedite proceedings also rests on whether anyone challenges the government’s legal opinions on each politician.

“In the event that any person who is the subject of a reference disputes the conclusion reached in any of the expert opinions anticipated above, the Attorney-General submits that that reference may need to be determined separately from the other references,” the government’s submission says

Senator Roberts has also yet to reveal the documentation he says he has supporting his claim that he was not a dual British-Australian national during last year’s election.

Fairfax Media has more of the government’s submission here.

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