Scottish Tory leader David McLetchie has told two former MSPs that they have "betrayed" the Conservatives by defecting to "a piddling little party".
David McLetchie: "Error of judgement"
Mr McLetchie said former Tory MSPs Lyndsay McIntosh and Keith Harding had made "a serious error of judgement".
He accused the pair of switching sides in a last-ditch bid to get themselves re-elected.
The former Tory MSPs announced that they were quitting the party to join the new centre-right Scottish People's Alliance.
Both had been front bench spokespeople for the Conservatives in the Scottish Parliament, but were unlikely to be re-elected after sliding down the rankings in their respective regional lists.
Mr McLetchie said: "Everybody knows what their motivation is. It's nothing to do with politics or convictions.
"It's a plainly opportunistic decision they have made reflecting the fact that they were not ranked.
"Would they be in the Scottish People's Alliance today if they were ranked number one in their respective regions?"
Lyndsay McIntosh defected to the SPA
Mr McLetchie also revealed that neither Mr Harding nor Mrs McIntosh had told him personally of their decision and that he had not spoken to either of them since.
He said both had "betrayed" their former Conservative colleagues and said they were guilty of a serious breach of trust.
The Tory leader also launched a withering assault on the SPA, which he described as "a piddling little party" that would win hardly any votes on 1 May.
"The Scottish People's Alliance will be no more than a temporary blip," he said.
Served with distinction
Mrs McIntosh said it had become clear when the Tories selected their list candidates for the Central Scotland region that she could not be elected.
She said: "It was clear five months ago that I could not be elected as a Tory. Since then I have seen out my term of office and, in the words of one senior Tory, I have served with 'distinction' until the very last day."
Mrs McIntosh is to stand as both a first-past-the-post candidate and as a prospective list MSP for central Scotland.
Mr Harding, who was the Conservatives' local government spokesman at Holyrood, will contest the Stirling seat for the SPA.