The figures - which will be supplied exclusively to PRWeek by TNS Media Intelligence for the weeks up to polling day on 5 May - show that 41 per cent of coverage of Labour was negative in tone.
Nine per cent of coverage of the Conservatives was negative, and just five per cent for the Liberal Democrats, as the two main parties focused their ire on each other.
While the majority of coverage for all parties was neutral, Labour suffered from Tony Blair being perceived as a liability to the party.
In terms of the issues, tax and spending gained the most broadcast exposure, followed by immigration, health, education and crime.
The analysis monitored the tone of coverage on BBC1's News at 10, Newsnight, Question Time, ITV News, Channel 4 News, Breakfast with Frost, Jonathan Dimbleby and the Today programme on Radio 4 between Monday 4 and Sunday 10 April.