WILLIE Rennie, the Scottish Lib Dem leader, has accused the Scottish Conservatives of aiding the rise of the SNP, as a furious row over tactical voting broke out between the two parties.

He claimed the Tories were putting "party before country" by campaigning hard in seats where the Lib Dems hope to hold off the challenge of the Nationalists.

In an outspoken attack, he accused David Cameron of "fuelling support" for the SNP by backing English Votes for English Laws and said George Osborne played a "bizarre tactical game" by talking up Nicola Sturgeon's performance in the first televised election debate.

He added: "Now the Conservatives in Scotland are getting in the way of our battles to stop the SNP in the 11 Westminster seats we hold in Scotland.

"The only result of their reckless actions would be to divide the non-SNP vote and let the SNP win."

Mr Rennie singled out North East Fife, the seat previously held by the retiring Sir Menzies Campbell, where he claimed the Conservatives were "also rans".

Another seat the Lib Dems hope tactical voting will help them defend is Gordon, which Alex Salmond hopes to take for the SNP.

"I don't doubt the Conservatives' loyalty to the United Kingdom but their actions show they are putting their party before their country.

"Thankfully, many traditional Conservatives are ignoring the overtures from the Conservative Party.

"In increasing numbers they are backing the local Liberal Democrats to stop the SNP."

Mr Rennie spoke out a day after Scottish Conservative leader Ruth Davidson issued an undisguised plea for Lib Dems supporters to vote Conservative "if you are looking for an anti-SNP candidate".

Yesterday she hit back angrily, accusing the Lib Dems of "peddling half-truths to try and save their own skins".

She said: "I have warned this week of the increasing desperation of the Lib Dems as they are set to lose their deposit all across Scotland.

"The pygmy politics of Willie Rennie to suggest that I should not be allowed to campaign on my home town patch with my mum and dad, in the area I grew up in, is utterly pathetic.

"Everybody is clear that the Scottish Conservatives are the most pro-union party and I stand by my record in the referendum."

Labour leader Ed Miliband has previously accused the Tories of forming an "unholy alliance" with the SNP in the hope the Nationalists will defeat Labour candidates across Scotland.

Peter Kellner, the president of pollsters YouGov, said tactical voting could prevent the SNP claiming a number of seats.

A YouGov found almost half of all Conservative and Lib Dem supporters were prepared to switch to Labour to keep out the SNP in a two-horse race between those parties.

In seats where the SNP and Tories were in a straight fight, one in three Labour and Lib Dem supporters would back the Tories.

Mr Kellner predicted tactical voting would help the Lib Dems save two seats, including Charles Kennedy in Ross Skye and Lochaber.