Mr Brown's leadership style was likened to porridge
A Labour peer has launched an attack on Gordon Brown's premiership saying it was like "porridge" compared with predecessor Tony Blair's "champagne".
Lord Desai said Mr Brown must "change his style" to be "more presentable".
He told the BBC recent opinion polls did not look good for Labour, ahead of local elections next month, but said it could "overcome these things."
Lord Desai, a leading economist, is not known to have spoken out against the party leadership before.
He told BBC News 24: "A lot of this is about perception. He [Mr Brown] doesn't seem to be able to tell people he's on their side and he can solve their problems.
"I really think somebody has to change his style and make him more presentable."
Lord Desai added: "He is a tremendous person in terms of thinking, policymaking, his seriousness, the question is going to convey to people that he feels their pain and that he is on their side?"
He said that as a Labour member for 37 years, his main concern was the party won the next election, but he believed voters were losing patience with Mr Brown's style of government.
"Blair was like champagne and caviar, Brown is more like porridge or Haggis. He is very solid, very nourishing but not exciting," he said.
The backbench peer denied he was stabbing the prime minister in the back, while he was out of the country on a tour of the US.
"I am not stabbing him at all, but if it was it would be in the front. I have said something openly, frankly," he told BBC News 24.
"Tony Blair had a style of communication and that's why, when you see Gordon Brown, you say 'Oh my God, how good Tony Blair was'," he added.
Earlier, he told the Evening Standard newspaper that the prime minister had appeared "indecisive" and "weak" and was "a worrier".
He said: "Gordon Brown was put on earth to remind people how good Tony Blair was."
Lord Desai, a professor of economics at the London School of Economics, is not known to have spoken out against the Labour leadership before
In his interview, he criticised Mr Brown's decision, while chancellor, to abolish the 10p starting rate of income tax - which opponents say will hit low-earners - calling it a "miscalculation".
Lord Desai said the 1 May elections for councils in England and Wales and the London Assembly and mayoralty were "going to be bad" for Labour.
He added: "If Labour loses in London there will be a real climate of fear... it would be absolutely traumatic for the party. At that point, backbenchers would look at the situation and say, 'How is all this going to work out for me?'. There would be real panic stations."
Lord Desai said Foreign Secretary David Miliband would be the best choice as next Labour leader and called Schools Secretary Ed Balls, a close ally of Mr Brown, a "repetition" of the prime minister.
On Wednesday, Chancellor Alistair Darling said the government had to "sharpen ourselves up" and deliver a "clear message of what we are about".
But Health Secretary Alan Johnson called Mr Brown "a serious man for serious times".