Former Scottish Secretary Lord Michael Forsyth attacked Ms Davidson after she disavowed a speech made in the Lords by another former Tory Scottish Secretary Lord Lang as splits opened in the Conservative ranks on how to fight the referendum.
Lord Forsyth said the Scottish Tory leader “ought to have been more careful with her comments”, putting this down to the fact “she’s new and a little inexperienced.”
He then further criticised her intervention, saying: “it’s always unwise to comment on something if you haven’t heard it”.
But a source close to Ms Davidson hit back at the peer who was one of her backers in the leadership election and helped her defeat frontrunner Murdo Fraser.
The source said: “Ruth Davidson has now been Scottish Conservative leader for longer than Lord Forsyth was Scottish Secretary.”
The SNP said the row showed disarray in the Scottish Conservative ranks.
SNP MSP Annabelle Ewing said: “Lord Forsyth’s intervention is further proof if it was needed that the Tories – and the unelected House of Lords - are completely out of touch with the debate in Scotland.
“While Ruth Davidson’s attempts to distance herself from Lord Lang’s ill-judged and offensive remarks did not come quickly or go far enough, at least she acknowledged that the language used was not acceptable.”