MELBOURNE (Reuters) – A crisis engulfing Australia’s parliament has widened after a key independent senator became the seventh parliamentarian referred to the High Court to determine if his dual citizenship makes him ineligible to sit in parliament.

Senator Nick Xenophon’s announcement on Saturday that he holds dual British citizenship comes as the future of Prime Minister Malcolm Turnbull’s government hangs in the balance, with question marks surrounding the eligibility of key members of his government and crossbenchers threatening supply should it be stripped of its one-seat majority.

That majority was placed in jeopardy earlier this week after Deputy Prime Minister Barnaby Joyce said he may be ineligible for parliament due to New Zealand citizenship by descent.

His father was born in New Zealand. Joyce has since relinquished New Zealand citizenship, but is awaiting the High Court ruling, along with several other politicians who believe they may have dual citizenship.

The citizenship crisis, based on a 116-year-old law which demands an elected lawmaker only have Australian citizenship, has rocked the Australian parliament, ensnaring three government members, three Green party MPs and Xenophon.

Xenophon said on Saturday he had received advice overnight from the UK Home Office that, due to a “rare peculiarity”, they considered him a British overseas citizen.

The senator, who was born in Adelaide, Australia, said his father, Theodoros Xenophou, was born in Cyprus and left there in 1951. Cyprus remained a British colony until 1960 when it gained independence.

“The great irony here is that my father left Cyprus in order to escape British colonial rule,” the senator said.

Xenophon had renounced Greek citizenship, which he received from his mother, but had not been aware he held possible British citizenship.

On Friday a member of Xenophon’s eponymous party in the lower house of parliament, Rebekha Sharkie, became the latest crossbencher to withdraw her support for the government on matters of confidence and supply, telling Fairfax Media the prime minister was showing “disrespect to the Australian community” by not standing down the ministers referred to the High Court from their cabinet positions.

While the government does not currently need the support of crossbenchers in the lower house to hold office, should the court rule Deputy Prime Minister Joyce ineligible, it could only survive with the support of at least one non-government MP.

Only one lower house crossbencher has not withdrawn their support.

Business leaders in the country have warned the dual citizenship chaos risks damaging the country’s standing among foreign investors.