The Tory lead over Labour has grown to nine points according to the latest pre-election opinion poll but both main parties saw their vote share drop as the Liberal Democrats gained ground.
An ICM survey for The Guardian put David Cameron's opposition on 38 per cent - down one point on that pollster's last results - with Gordon Brown's governing party dropping two points to 29 per cent.
The Liberal Democrats - perhaps boosted by the popular showing of economics spokesman Vince Cable in this week's televised debate of would-be chancellors - gained four to stand at 23 per cent.
ICM surveyed 1,003 adults across the UK by telephone on March 30 and 31.
Meanwhile, the Daily Telegraph said another 14 senior business figures - including former McLaren Formula One team boss Ron Dennis and Simon Fox, the chief executive of HMV Group - had joined the public endorsement of Tory tax plans.
David Cameron and George Osborne have promised to halt the planned National Insurance rise if they win the election.
