South Australian Liberal MP Nick McBride has quit the party in a move his former leader says had a degree of inevitability.
Mr McBride, who holds the southeast seat of MacKillop, cited issues with the party's factions for his decision which will swell the crossbench ranks in parliament to five and cut the number of Liberals to 15.
"I understand some people may be disappointed with my decision, given I was elected as a Liberal member," he said.
"I hope those people can understand I have found it increasingly difficult to represent the party that I believe is trying to ostracise one of its own.
"Despite what the Liberal party may say, there are factional pressures at play which have resulted in disunity."
Leader David Speirs said he didn't believe there was anything he could have done to keep Mr McBride in the Liberal fold.
"There was an inevitability about this. Nick McBride has had a range of gripes with the Liberal Party for some years," Mr Speirs said.
"I've bent over backwards for Nick McBride. I've gone to his seat seven times since becoming leader of the party 16 months ago.
"There is very little I could have done to keep Nick McBride in the tent."
In relation to claims of factional pressures, Mr Speirs said he believed the Liberals had never been more united and didn't consider his leadership to be at risk.
He said Mr McBride was looking for a "trigger" to leave and while he was disappointed he was not surprised.
The opposition leader said he also suspected Mr McBride would have been defeated in a MacKillop pre-selection vote in coming months had he stayed a member of the Liberals.
"In some ways, there's a sense of relief we've got certainty now. The speculation has gone on for months and months," Mr Speirs said.
Leader of government business in the house Tom Koutsantonis said Mr McBride's decision was further evidence of the Liberal Party's shift to the right.
"It is clear this is no longer a party for traditional Liberals of the sensible centre-right," he said.
Mr McBride's move can only strengthen Labor's grip on power in SA with the party having 27 of the 47 seats in the House of Assembly.
However, the former grazier would be expected to support a Liberal government in the event of a hung parliament after the next election in 2026 and has ruled out taking any ministerial role in the current government.
Fellow independent Geoff Brock serves as the Minister for Regional Roads, Local Government and Veterans' Affairs in the Labor cabinet.
Another crossbencher, Dan Cregan, who left the Liberals before the last election, is the parliamentary speaker.
