FORMER Nick Xenophon Team candidate Tim Storer, who missed out on a seat at the last federal election, has made a shock grab for Mr Xenophon’s Senate seat, leaving the party “surprised”.

The party has already picked former submariner Rex Patrick to take that spot. In a statement, the party said it was “shocked and disappointed” about Mr Storer’s move.

Mr Xenophon officially quit the Senate this week after the High Court cleared him of being a dual ­citizen.

If the High Court had not cleared him, he would have lost his seat and a vote countback would have delivered the powerful spot to Mr Storer, an Adelaide businessman who was fourth on the ticket.

But as it turned out, there was a casual vacancy and the party chose Mr Patrick, as is its right, to fill the party’s third Senate seat.

The situation is complicated because the South Australian Parliament has to rubberstamp that federal nomination.

Normally that would mean Mr Patrick would sail through. But in a surprise twist, Premier Jay Weatherill stood up in Question Time on Wednesday and announced he had received a “private and confidential” letter from Mr Storer’s lawyers.

“Mr Storer asserts rights in relation to the filling of the casual vacancy,” Mr Weatherill told Parliament.

“I have asked the Attorney-General to seek legal advice from the Crown Solicitor’s Office to allow him to inform the deliberations of the joint sitting.”

That means both houses will sit on November 14 to ­decide who will replace Mr Xenophon.

Mr Xenophon said that to choose anyone apart from the party’s pick would “absolutely fly in the face of the spirit and intent” of the Constitution.

“The changes to Section 15 of the Australian Constitution in the late 1970s were all about ensuring that it was a nominee of the party that filled a casual Senate vacancy,” he said.

NXT also announced this week that the federal party would be called SA Best (Federal) in line with the name of the state party.

The party has asked for Mr Storer’s lawyer’s letter to be made public and is seeking advice about Mr Storer’s membership of the party.

He must be a member to take the seat.

“NXT is particularly surprised by Mr Storer’s actions as, until recently, he had expressed a strong wish to run as an SA Best candidate in the upcoming SA state election,” the party said in a statement.

The Advertiser has contacted both Mr Storer and Mr ­Patrick for comment.

In a further shake-up, ­Senate President Stephen Parry will resign from the Senate on Thursday after becoming the first Liberal member to be embroiled in the dual citizenship scandal.

He said he had received advice from the UK Home Office confirming he was British.

Mr Parry, from Tasmania, sought advice after the High Court ruled on the eligibility of seven parliamentary colleagues last week.

Labor criticised Senator Parry for not addressing the issue sooner.

Former Liberal junior minister Richard Colbeck is expected to make a comeback and replace Senator Parry.

But tensions between the Liberals and Nationals have been further strained over the decision about who would be handed the lucrative role after NSW National John “Wacka” Williams put up his hand.

Acting Prime Minster Julie Bishop said she could not rule out more casualties of the dual citizenship sweep but did not support an audit on all MPs.