President of the Senate, Senator Stephen Parry, during estimates. Credit:Alex Ellinghausen In his statement, Senator Parry said the British Home Office had confirmed his dual citizenship on Wednesday and that his departure was a "rapid and an unexpected event" after 12 years in Parliament and six and a half years as deputy president and president. "I will not have the usual opportunity to address you in the Senate one last time. I wish to thank all of you as colleagues, many of whom I regard as good friends – from all quarters of the chamber – for your support and confidence in me," he said. It's understood the Prime Minister's office was taken by surprise by the Senator's initial announcement on Tuesday. Well-regarded Nationals senator John "Wacka" Williams has emerged as an early candidate for the vacant job of Senate President.

President of the Senate Stephen Parry at Canberra Airport Credit:Alex Ellinghausen The Nationals have never held the post of Senate president and, amid tensions in the NSW branch of the Coalition, the Liberals will likely fight any move to take the post. As the citizenship crisis deepens, Mr Turnbull is now under growing pressure from within to agree to a full audit of not just all MPs elected at the last election but all candidates. Liberal senator Stephen Parry, pictured alongside Prime Minister Malcolm Turnbull. Credit:Alex Ellinghausen Liberals Eric Abetz, Craig Kelly and Llew O'Brien​ and former NSW premier Barry O'Farrell on Wednesday called for an audit of the citizenship status of all federal MPs after Senator Parry became the eighth MP caught up in the citizenship fiasco.

Senator Abetz said an audit was needed to ensure the integrity of the Parliament; Mr Kelly complained the government's "good work" was being "drowned out" by the citizenship fiasco. President of the Senate Stephen Parry shakes hands with Governor-General Sir Peter Cosgrove at the opening of the 45th Parliament. Credit:Alex Ellinghausen Mr Kelly argued Labor candidates were elected in July 2016 who had trailed Coalition candidates on the primary vote but had won with Greens preferences. "They basically leap-frogged a Liberal candidate based on Greens preferences. How many of those Greens candidates were actually eligible?" Greens leader Richard di Natale has already backed a full audit, but the acting leaders of the Liberal, Nationals and Labor parties – Julie Bishop, Nigel Scullion and Tanya Plibersek – all pushed back against an audit.

Meanwhile two Labor MPs – Tasmanian MP Justine Keay and Queensland MP Susan Lamb – could be under a cloud over their citizenship status, according to constitutional law experts. Ms Keay and Ms Lamb have released timelines of the steps they took to relinquish their dual citizenship; Ms Keay began the process on May 9, 2016 and Ms Lamb began on May 23, 2016. But neither MP will release letters from the British Home Office that would show the exact date their application to renounce was processed. This is despite Opposition Leader Bill Shorten releasing a similar letter detailing his British citizenship renunciation. Media advisers for both MPs refused to answer questions on Wednesday and referred all questions to Mr Shorten's office. The Opposition Leader's office would only refer to previous statements and refused to answer questions. If the two MPs' applications to renounce were processed after June 7, when nominations for the 2016 election closed, the pair may not have been validly elected according to Professor George Williams.

"If they received a letter saying their citizenship has been renounced by the date of their nominations they are safe. If that letter has not been received by that time of nomination then questions need to be asked about whether they have taken all reasonable steps," he said. Professor Anne Twomey said there was "certainly reasonable doubt" about the status of the Labor pair. It was possible, she said, the High Court could find they had taken "all reasonable steps" to renounce British citizenship and they would - if the matter was tested - be found to have been validly elected. "But alternatively the High Court could take a strict position and say it's the date of nomination [for renouncement that needs to be met], and that's it, you are out." Loading

The High Court's judgement on the so-called "citizenship seven" found "the temporal focus for the purposes of s 44(i) [which pertains to dual citizens] is upon the date of nomination [in this case, June 7, 2016] as the date on and after which s 44(i) applies until the completion of the electoral process." The Court also wrote that "a person who, at the time that he or she nominates for election, retains the status of subject or citizen of a foreign power will be disqualified by reason of s 44(i)", though it also allowed for a candidate to have taken "all steps that are reasonably required by the foreign law to renounce his or her citizenship".