Gordon Brown has been accused of insulting the intelligence of British business by one of the country's top executives.
Sir Stuart Rose, executive chairman of Marks & Spencer and a member of the Prime Minister's business council, hit out after Mr Brown claimed business leaders had been "deceived" over Labour's planned rise in National Insurance.
The chiefs of more than 60 top companies have backed the Tories' opposition to the rise in an intense political row which has so far dominated the General Election debate.
Mr Brown suggested on Wednesday that business leaders had been "deceived" by the Tories.
Sir Stuart, who signed a letter criticising the National Insurance rise last week, told BBC Radio 4's Today programme "It's unfortunate that we have been dismissed. This is an important argument and to insult the collective intelligence of 60-plus chief executives is unhelpful.
"This is not a political point so much as a point about where tax should be levied. Everybody knows that the country needs to sort itself out and this was a serious attempt to have a voice on the subject."
Mr Brown claims Tory plans to scrap the bulk of the National Insurance rise pencilled in for next April would take £6 billion out of the economy.
Sir Stuart's comments come as Mr Brown was stepping up his attack on the Tories over National Insurance in the belief that Labour can benefit from the debate about tax and spending. But the M&S boss signalled a growing backlash against the Prime Minister among the business community. Another of the signatories of the letter, Risk Capital Partners founder Luke Johnson, has also described Mr Brown's remarks as "insulting".
Meanwhile, Gordon Brown insisted he was fighting for "five more years" as Prime Minister, after Business Secretary Lord Mandelson recently hinted that Mr Brown might not serve a full term, if re-elected.
Asked about Lord Mandelson's remarks, Mr Brown told BBC Radio 4's Today programme: "I will be standing for the next five years."