The Liberal Democrats were accused of “deliberately” setting out to mislead voters “in the most cynical way possible”.
The charge was in response to election material in the form of a public letter in which an alleged former Conservative supporter Audrey Dunsmore said she was “switching” to the Lib Dems.
“As someone who voted Conservative for many years, I am glad the Liberal Democrats have been able to stop the extremes of David Cameron and co in government,” she said.
But it has emerged Ms Dunsmore stood has long term connections with the Lib Dems. She was their council candidate in Rosyth three years ago and was recently pictured with UK and Scottish leaders Nick Clegg and Willie Rennie.
Scottish Conservative deputy leader Jackson Carlaw has written to Scottish Lib Dem leader Willie Rennie demanding he withdraws the letter and apologises to voters for the deception.
In his letter, Mr Carlaw said elections should be conducted in a spirit of honesty and openness, but Mr Rennie was attempting to mislead voters by getting Ms Dunsmore to pose as a Conservative supporter “when, quite clearly, she is not”.
“There is no other way of putting this: your party is deliberately setting out to mislead voters in the most cynical way possible,” he said.
But the Lib Dems were unapologetic. A spokeswoman said: “We’re more than happy to confirm that Audrey Dunsmore used to vote Conservative and is now, like so many others, backing our Lib Dem candidates, as set out clearly in her letter.
“This is a silly attempt by the Conservatives to throw up dust where there isn’t any to throw.”