Scottish Conservative voters are being urged to abandon the party after it elected Russell Findlay as its leader.
Liberal Democrat leader Alex Cole-Hamilton also criticised Mr Findlay for previously backing Liz Truss as prime minister.
He said many voters feel the Scottish Tories have “moved far away” from the leadership of Ruth Davidson.
He also accused the candidates in the UK Tory leadership contest of “lurching to extremes”.
Mr Cole-Hamilton said voters want a political party that is “caring and sensible” instead of those who “cheered on Truss’s economic chaos”.
He said his comments, made just before Mr Findlay leads the Tories for the first time at First Minister’s Questions on Thursday, will form the basis of a letter he is sending Conservative voters.
Mr Findlay won the leadership contest on Friday, beating former deputy leader Meghan Gallacher and veteran MSP Murdo Fraser.
He replaces Douglas Ross, who announced his intention to step down during the general election campaign after four years in the job.
The Lib Dems returned five Scottish MPs in July, one more than the Tories, and south of the border the party beat the Conservatives across huge swathes of England.
Mr Cole-Hamilton said many people feel “disenchanted with politics” and “politically homeless”.
He added: “Over the past days, I’ve spoken to many people who had previously voted for the Scottish Conservatives. They now feel that the party has moved so far away from that which was once led by Ruth Davidson.
“People want a politics that reflects our country: caring, sensible and sees the benefit in working together with our neighbours.
“That inclusive approach is now completely absent from the Conservative Party today.
“Now all that’s left is a party in decline. A party now led in Scotland by someone who cheered on Liz Truss’s economic chaos.”
Mr Findlay endorsed Ms Truss, whose premiership only lasted a couple of months, during her Tory leadership campaign in 2022.
He has since apologised for his support and said he made a mistake.
Former prime minister Rishi Sunak’s successor as UK Tory leader will be announced on November 2 following a lengthy leadership battle.
Kemi Badenoch, James Cleverly, Robert Jenrick and Tom Tugendhat have all put their hat in the ring.
Mr Tugendhat, considered to be on the more moderate side of the party, has won the backing of several Tory MSPs.
But Mr Cole-Hamilton said that even after Ms Truss, the Tories are “moving backwards and lurching to extremes”.
In his pitch to Conservative voters, he said his party can be the one to get the SNP out of power in Holyrood.
“We won more seats than the Scottish Conservatives at the last election and showed we can beat the SNP in huge swathes of Scotland,” he said.
“We can take down the acid yellow wall of the SNP in the 2026 Holyrood election.
“By backing the Scottish Liberal Democrats, you can guarantee hard working local champions who will put your priorities first.
“I love our country and want to see the best for it, that’s why I know we need to get the SNP out of power.
“The Scottish Liberal Democrats are ready to do just that.”
A Scottish Conservative spokesman said: “Alex Cole-Hamilton might be the poster boy for the cosy left-wing consensus at Holyrood and the Scottish political establishment that prioritises fringe obsessions over issues that affect families in the real world.
“The Lib Dems lined up with the SNP and Labour to support radical gender reforms that were completely at odds with the values of mainstream Scotland.
“Alex Cole-Hamilton then thoroughly embarrassed himself personally during the scandal where the double rapist Isla Bryson was sent to a women’s prison, which demonstrated how detached from the real world the Scottish Parliament has become.
“Under Russell Findlay’s leadership, the Scottish Conservatives will be different. He gets why people have lost trust in politics and we will stand up for everyone who just wants their politicians to show some common sense, for a change.”
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