Under pressure: Prime Minister Malcolm Turnbull. Credit:Fairfax Media Mr Shorten will be placing stringent conditions on Labor's support for the plan and will be seeking an undertaking from Mr Turnbull that Mr Alexander's case - should he be found to be a dual citizen - be dealt with immediately. The demand stems from Labor's claim the government is trying to "skate through" the crisis until the summer break, avoiding a scenario where it may have to face the final weeks of Parliament without both Mr Alexander and expelled National Barnaby Joyce. Citizenship experts agree Mr Alexander is likely to be a British citizen by descent after Fairfax Media revealed his father was born in England before moving to Australia as a young child. Mr Alexander has never renounced British citizenship and cannot say for sure whether his father did so in the two years between when the concept of Australian citizenship was introduced in 1949 and John's birth in 1951.

John Alexander campaigning in Bennelong in 2013. Credit:Mick Tsikas If he resigns or is found ineligible it would spark a byelection in his Sydney seat of Bennelong. There is speculation that the 67-year-old may not stand again, potentially making it harder for the government to retain the seat. The former tennis champion is a strong local member and has built his seat's margin by nearly 7 per cent since he first won it in 2010. But a new Liberal candidate could leave it vulnerable, putting Mr Turnbull's majority at risk. Demanding answers: Maxine McKew says voters are "unimpressed with the present shenanigans in Canberra". Credit:Joseph Feil The woman vanquished by Mr Alexander in 2010 – former TV star Maxine McKew – said the voters of Bennelong had a right to answers. She predicted a byelection could be a close-run thing, despite Mr Alexander's comfortable margin.

"Bennelong is full of informed voters who pay attention and I suspect they are unimpressed with the present shenanigans in Canberra," she said. "Labor can certainly mount an effective competitive campaign next time around." Liberal member for Bennelong John Alexander during his Maiden Speech at Parliament House. Credit:Ben Rushton Labor frontbencher Penny Wong said the opposition would be happy to fight to regain Bennelong, which Ms McKew won from prime minister John Howard and held for one term. Senator Wong said Mr Turnbull's proposal was "not good enough" and should not be used to cover up Mr Alexander's woes. "John Alexander needs to be referred to the High Court," she said. "Mr Turnbull should not allow the House of Representatives to turn into a protection racket for John Alexander and anyone else simply because Mr Turnbull doesn't want to risk his numbers on the floor of the House."

Mr Turnbull conceded there could be "consequences" for his grip on power if more lower house Coalition MPs were found to be ineligible, either as a result of being outed by the media or as a result of his new disclosure regime. But Mr Turnbull pushed back against a call from one of his own backbenchers for a constitutional change that would allow dual citizens to sit in Parliament, saying it was "questionable" if the Australian people would get behind such a move. Constitutional and immigration law experts say Mr Turnbull's plan is a step forward but contains too much subjectivity – meaning it places too much weight on an MP's beliefs about their status, rather than the legal facts. University of New South Wales constitutional law expert Sangeetha Pillai, said the proposed requirements were overly reliant on MPs' understanding. She proposed changes including shortening the 21-day declaration period, extending the specification of birthplace to cover grandparents, and more documentation of actions to sever foreign ties. Loading

Under the British Nationality Act 1948, people born to British fathers are automatically given UK citizenship by descent. This is the law that conferred British citizenship on former senator Nash and former One Nation senator Malcolm Roberts, who were kicked out of the Senate by the High Court last month. Former Senate president Stephen Parry resigned from Parliament last week after revealing he was a dual British citizen through the same law.