A Labour MP has been accused of distributing an advertisement to thousands of homes stating: "Tories bite off babies' heads".
Glasgow South West MP Ian Davidson was said to have placed the ad in a free newspaper, The Govan & Glasgow South West Press, which is distributed to 20,000 homes in his constituency.
Scottish Conservative leader Annabel Goldie said she was sent a copy of the newspaper anonymously.
She said: "If that is what the Labour Party in Scotland is reduced to, that to me says it all about the complete vacuum at the heart of their policy, and the complete vacuum at the heart of their vision for Scotland."
Miss Goldie believes the advert will backfire on Labour on the eve of the Scottish Parliament election, claiming it has already convinced at least one family of voters to switch from Labour to the Tories.
She said: "A Labour voter phoned me a few nights ago to say that their family, who have been traditional Labour voters in Scotland for a long time, was thinking for the first time of voting Conservative and wanted to speak to me about it.
"I told them about the advert and this erstwhile Labour supporter said: 'I've heard enough. The Conservatives are getting my vote'."
The freesheet is edited by journalist John Maclean and published by his company The Glasgow Press.
Mr Maclean said the advert was contained in a section prepared by Mr Davidson for the newspaper giving a summary of his activities in the constituency. He said he had approved the ad prior to distribution.
Mr Maclean said: "I thought it was quite funny and I knew that no-one would take it seriously, so I left it in.
"I apologise if it has damaged the Tories' chances of winning a seat in the south of Glasgow, although I don't think they had much chance of doing that anyway."
Mr Davidson was not immediately available for comment.