Nick Xenophon's representative in the South Australian Parliament, MLC John Darley, has quit the party and has slammed its figurehead as a "complete dictator".

Mr Darley resigned a day before he was expected to be expelled for siding with the Labor Government against party policy.

Senator Xenophon called for Mr Darley to go one step further and resign from Parliament, suggesting the MLC had been elected under his brand.

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But Mr Darley has refused to quit.

"Absolute nonsense. Rubbish. There's no way I'm quitting the Parliament," Mr Darley said.

"I will endeavour to see out my term until 2022 and as a result of his actions I will make sure I'm still there in 2022.

"He [Senator Xenophon] adopts a dictatorial approach. A complete dictator. It's either Nick's way or the highway.

"He will not entertain any opposition at all. In fact, he runs away from opposition."

Conflict brewing for months

Mr Darley said his conflict with the Xenophon parties, Nick Xenophon Team (NXT) and SA Best, dated back to April.

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"One person in the party thought they had a deal with me that I would retire soon after the 2014 election. There was never ever such a deal," the 80-year-old said.

Connie Bonaros, Nick Xenophon and John Darley in 2014. ( ABC News )

Matters came to a head last week when Mr Darley voted with the Labor Government on electoral reform.

Mr Darley voted in favour of instructing voters to simply vote one above the line, rather than NXT policy to instruct voters to number six boxes above the line on the Legislative Council ballot paper.

Members of NXT fear that decision could harm the party's chances of winning voter influence in the Upper House.

"If I didn't vote that way, it risked us having the same voting procedure that we had in the past," he said.

"Nick said to me he'd rather have that than the Government position.

"No-one else in the chamber would accept that position and so I voted in favour of the Government's amendment."

Mr Darley acknowledged breaking party rules by shifting his vote.

"Absolutely I did and I tried to explain that to Nick, but every inch of the way I couldn't get to him."

Resignation averts expulsion

Senator Xenophon accepted Mr Darley's resignation and wished him well.

Senator Xenophon accused Mr Darley of breaching party rules. ( ABC News: Adam Kennedy )

"People need to know that he was due to be facing expulsion at a party meeting tomorrow morning in Adelaide, as a result of breaches to party rules," he said.

"Obviously his resignation has averted that expulsion.

"At a personal level I genuinely wish him well but politically he needs to do the right thing and resign from Parliament because he is no longer part of the group that helped get him elected."

Mr Darley first entered Parliament in 2007, replacing Nick Xenophon, who had resigned from the SA Legislative Council to run for a seat in the Senate.

It is not the first falling out Senator Xenophon has had with his partners in the SA Parliament.

In 2007, fellow MLC Ann Bressington quit a parliamentary partnership with him amid an extraordinary outburst in parliament in which she described him as a "chameleon" and a "typical politician".

Mr Xenophon said the party's candidate selection methods now were "very different from what happened well over 10 years ago".

He said the process was "very thorough". He also said "you also need to have discipline if somebody breaks the rules; there needs to be consequences".

Senator Xenophon said Mr Darley's resignation had cleared "the decks for the state election".

"We will have a new team of candidates chosen through a very thorough process and get on with things," he said.