Tory MSP Brian Monteith has described how he had no choice but to resign the whip after he admitted plotting against the party's former leader.
Brian Monteith said he had been guilty of misjudgement
He left the Tories' Holyrood group after it was revealed that he had briefed against David McLetchie.
It emerged that prior to Mr McLetchie's exit on Monday, Mr Monteith e-mailed a Sunday newspaper suggesting it run an editorial calling for his departure.
Mr Monteith said when that was made public, he had no option but to quit.
He told BBC Scotland: "I have to take the blame for briefing against my leader.
"I accept that fully. It was clearly a misjudgement, not just to do that, but to trust the editor of that particular paper.
"So I offered my resignation from the group. It was the proper thing to do."
The Mid Scotland and Fife MSP made the suggestion in an e-mail to Iain Martin, editor of the Scotland on Sunday newspaper, in mid-October.
That was almost two weeks before Mr McLetchie's departure amid continuing controversy over his taxi expenses.
Mr Monteith said: "I knew the Scotland on Sunday newspaper was going to reveal my e-mails saying that David McLetchie should resign.
"Because they were going to reveal them, I submitted them myself to the party chairman and he said he would have to withdraw the whip."
In six days, the 18-member Tory group at Holyrood has seen the loss of a leader and the exit of an MSP.
Annabel Goldie said disloyalty would not be tolerated
Annabel Goldie, who looks set to be elected as the new party leader without opposition, was unequivocal in her condemnation of the affair.
She said: "The matter was the subject of a very robust investigation.
"What ultimately emerged made it crystal clear that behaviour which was completely unacceptable to a member of the Conservative group had taken place and there was only one possible course of action to deal with that.
"We cannot and will not tolerate disloyalty of such a material nature. It's unacceptable."
Mr Monteith, who could be expelled from the party, said he expects to stay on as an MSP until 2007.
Responding to the latest development, a Scottish Labour spokesman said: "It will surprise nobody that the Tories are on the brink of imploding.
"As their leadership contest in the Scottish Parliament demonstrates, they are the party no-one wants to lead, on a downward spiral towards political obscurity and oblivion.
SNP deputy leader Nicola Sturgeon MSP said: "Friday's events are further proof that the anti-Scottish Tories simply can't be trusted.
"Rather than standing up for Scotland, they are fighting and briefing against each other, and that's why they are on course for electoral meltdown."
Mr Martin said his newspaper would comment on the matter in this weekend's edition.