A leading centre for independent economic research has said the best evidence currently available suggests the 50p tax rate will raise "little revenue" and make a "marginal contribution" to reducing the budget deficit.
The Institute for Fiscal Studies said the best estimate, provided by HM Revenue & Customs (HMRC) in 2012, suggests that cutting the 50p rate to 45p could reduce revenues by about £3.5 billion in 2015-16 if there was no change in behaviour by affected individuals.
However, once one allows for a change in behaviour, HMRC's central estimate was a cost of just £100 million, a sum the IFS describes as "a very small amount of money".
Ed Miliband answered questions for the first time this afternoon about his plans to re-introduce the 50p rate of income tax.
Politicians at both ends of the political spectrum need to be more honest about the true motivations behind their tax policies.
Ed Balls has said Labour would restore the 50p tax rate for those earning over £150,000 if the party wins the next election.