In a blow to struggling Labour the ICM/Guardian survey showed 40% had confidence in the Tory Chancellor and Prime Minister on the key issue, up from just 28% in June amid signs of a growing economic recovery.
The dramatic stretching of the gap came despite continued public pessimism about the prospects for personal finances, with more people expecting their situation to worsen (29%) than improve (24%) over the next year.
Labour has made the rising cost of living a key theme of its attack on the coalition's handling of the economy.
Mr Miliband is under fire from some quarters within his own party for failing to set out sufficiently clear economic and other policies to attract voters and a "deafening silence" over the summer holiday period so far.
There was relatively better news for the Opposition in the overall voting intention figures, which showed it regaining its recent slim lead over the Tories, who drew level last month.
The latest poll put Labour down one point on 35% while the Conservatives shed four points to stand at 32%.
Most of those lost voters were picked up by the UK Independence Party which gained three points to 10%, with the Liberal Democrats gaining one point at 14%.
ICM Research interviewed a random sample of 1,001 adults by telephone on August 9-11.