Nick Clegg has accused the Conservatives of undermining Britain's economy by "stoking up fear" about a fall in the stock market.
The Liberal Democrat leader is set to claim David Cameron and George Osborne are deliberately trying to destabilise the pound and reduce the government's ability to borrow in what he will call "a crude form of blackmail".
It follows comments by shadow business secretary Ken Clarke that voters should be wary of backing the government for a fourth term because it would result in "financial crisis".
"There is nothing positive in the Conservatives' election strategy. It's built entirely on the hatred of Gordon Brown, stoking up fears of a broken society and now threatening economic meltdown," Mr Clegg will tell party workers later today.
"It's a strategy that is completely negative and without hope, and it's becoming increasingly obvious that people aren't going to fall for it."
The attack mirrors Labour criticisms of the opposition for "talking down the economy".
Mr Clarke told a City audience in Canary Wharf on Friday that he feared a fourth term of Labour would wreck Britain's recovery from the recession.
"Sixteen months on, as we watch the cost of borrowing soar, and the pound fall, we can see clearly that we are in a crisis still and cannot complacently assume that we are getting out of it," he said.
"This is not because of plain speaking from the opposition, but because the markets could take fright over the prospect of the irresponsible, profligate Gordon Brown government somehow hanging onto office for another five years."