Harman and Osborne at odds over 'tone' of election campaign
Senior Labour and Conservative figures have clashed over of the "tone" of the general election campaign.
Harriett Harman accused the Conservatives of "negative campaigning" which "undermines our democracy".
Chancellor George Osborne rejected the charge and said his party was setting out a "positive vision".
The comments came after Defence Secretary Michael Fallon said Ed Miliband would "stab the UK in the back" if he was prime minister.
Mr Fallon alleged that Labour could put the UK's nuclear weapons system at risk by doing a "grubby deal" with the SNP - which opposes nuclear weapons - to form a government.
The defence secretary said Mr Miliband had "stabbed his own brother in the back" to lead Labour and was now "willing to stab the UK in the back" by doing a deal on Trident with the SNP "to become PM".
Responding to the comments, Ed Miliband said the defence secretary had "demeaned himself and demeaned his office".
'Turns people off'
Labour deputy leader Harriet Harman told the BBC's Andrew Marr Show that she had encountered many people who did not intend to vote in the election on 7 May.
She argued: "To have accused Ed Miliband of being somebody who would stab the country in the back, I think that is negative campaigning - obviously they hope it's going to work - but actually it undermines our democracy, because it turns people off."
She claimed that her party's characterisation of David Cameron and George Osborne as "posh boys" was "quite different".
"We're saying they're standing up for people at the top and everybody else has been suffering and the recovery hasn't reached people, but that is quite different from saying that, as prime minister, Ed Miliband would stab this country in the back."
Conservative Chancellor Mr Osborne told the same programme: "Harriet and I went to the same school, so the 'posh boy' attack always sounds a bit thin when coming from her."
The chancellor said: "We've got a really positive vision for this country and, actually, I've found this campaign enormously energising and exciting.
"I go round the country and people are switched on, people do care about this country's future."
He added: "People can't sit this election out, you can't vote for a protest party. You've got to choose between Ed Miliband in Downing Street and David Cameron in Downing Street."