"When there is a threat to unity, I’m prepared to stand up and squash it," Mr Weatherill told Fairfax Regional Media in Whyalla on Friday.

Mr Weatherill's comments followed an extraordinary morning of political twists and turns which threatened to derail his government less than 50 days out from the state election.

It began after Member for Napier Michael O'Brien announced that he was prepared to step aside from his electorate to make room for out-going federal Senator Don Farrell.

“Don and I go back 30 years. We’re extremely close friend and it was my view that he would be a great loss to public life so I rang him on the Sunday morning and put the offer to him,” Minister O'Brien said.

Mr O’Brien said he offered his seat the morning after the federal election in 2013 when it became clear Senator Farrell would lose his senate spot.

On hearing this, Mr Weatherill threatened to resign.

Within an hour, Senator Farrell backed down from the move, saying it was clear he was not welcomed by Mr Weatherill.

Mr Weatherill later said it was effectively a "try on" by Senator Farrell and others and the situation had been resolved.

“I want to make sure that the divisions and disunities that have plagued other political parties, whether it be the South Australian branch of Liberal party or our Labor colleagues, didn’t play itself out in the South Australian Labor party," he said in Whyalla.

“My senior colleagues stood up with me and stared down what was effectively a try-on. 

“What it tells people is that when there is a threat to unity, I’m prepared to stand up and squash it ... The thing that irritates people most is all the black backroom deals and discussions behind closed doors, all the faceless men, that’s over.”

The premier said a replacement for Minister Michael O’Brien would be allocated as quickly as possible.

“We’ll reallocate his portfolios in the six weeks that remains and we’ll choose a replacement for his seat,” Mr Weatherill said. 

Minister O’Brien told the ABC he had not been forced to make way for Senator Farrell.

Napier predominantly covers the working class suburbs of Davoren Park, Elizabeth West, Elizabeth North, Smithfield, Blakeview and Craigmore but also extends into One Tree Hill and Uleybury.

Mr Weatherill said he was concerned that the events that had unfolded since Senator Farrell’s announcement could reflect badly on the state Labor party.

“We’ve seen all of this nonsense at a federal level, the divisions and disunities, we don’t want that in South Australia,” Mr Weatherill said.

“We don’t want to import all of that division and disunity in South Australia, that’s why I’ve made the judgement that I’ve made about what should happen with future pre-selections.

“People have to make the right choice about backing unity and stability and the clear sense of purpose about South Australia’s future, or they can turn back to the nonsense we saw at a federal level.

“I think it would destabilise the party if we were to choose the other choice.

“We’ve got to present a convincing argument at the next state election, there needs to be clear unified leadership with a clear purpose.

“We’re laying out a very positive plan for South Australia’s future; I don’t want anything to get in the way of that.

“Anything that threatens that, it’s my responsibility to repel that threat, that that’s what I’m doing here.”

Liberal Member for Hammond Adrian Pederick said he was not surprised by Friday morning's "unbelievable" Labor party scuffle.

But he said internal Labor business was a matter for his opponents to worry about.

"From my perspective locally, I need to make sure I win the seat of Hammond," he said.

"We've got our strong policy program, we're rolling that out, and we're showing we can have a strong Liberal government in March.

"We're concentrating on what we need to do and they can concentrate on their own dysfunction."

Labor's Member for Light Tony Piccolo said he had no comment on the situation but Independent Member for Frome Geoff Brock described it as a "hell of a shock".

Mr Brock is based in Port Pirie, in the state's Mid North.

“Michael O’Brien is one of the best ministers I’ve dealt with,” he said.

“That’s the factions,” Brock said of Farrell being parachuted into the seat of Napier.
“It’s a hell of a shock.”

Liberal member for Stuart Dan van Holst Pellekaan said the situation was a mess.

 “This is a mess the Labor Party has to deal with and doesn’t change my focus on doing everything I can for Port Augusta and the rest of our electorate," he said.

“Everyone knows that I believe a Liberal government would be much better for our state than Labor – we just have more proof now.”