Gordon Brown came under stinging attack from within his own party today when a leading Labour peer described him as weak and indecisive and said that his only purpose in life was "to remind people how good Tony Blair was".

The criticism from Lord Desai, an Indian-born economist, was the latest in a series of humiliations for the Prime Minister as he makes a three-day visit to the United States.

It was published as Mr Brown prepared to meet Barack Obama, Hillary Clinton and John McCain – the three presidential hopefuls – at the British Embassy in Washington.

Coming from a respected, if outspoken, party elder, it was also the most damaging.

In an interview with London's Evening Standard, Lord Desai said that the combination of an economic downturn and Mr Brown's presentational weaknesses now made it "very difficult" for Labour to win the next election. He said that many within the party were now turning their mind to who would succeed him as leader.

"Gordon Brown was put on earth to remind people how good Tony Blair was," Mr Brown told the newspaper. "It is a bit like William Hague who is a far better shadow foreign secretary than he was a leader of the Conservative party."

Lord Desai's comments followed the revelation earlier this week that his own trade minister, Lord Jones of Birmingham, was planning to bow out of frontline politics so as not to have to back him at the next election.

It also came the day after Alistair Darling, the Chancellor and one of Mr Brown's closest allies, admitted that the Government had to "sharpen up" its act.

Lord Desai, 67, has worked at the London School of Economics, where he is now an emeritus professor, since the early 1970s. He has also been a leading light in the Islington South and Finsbury Constituency Labour Party and was made a life peer in 1991 as Lord Desai of St Clement Danes, in Westminster.

In an outspoken interview, Lord Desai compared Mr Brown's style to "porridge, or maybe haggis: it is not very persuasive if you don't already agree with him".

He added: "He is a worrier with an academic approach to solving problems, but that does not always reassure people when they feel uncertain."

The interview was published as David Cameron, the Tory leader, launched his party's local election campaign with a speech in Dewsbury.

The peer said the outcome of those elections, especially in London, would largely determine the future of Mr Brown's leadership.

Asked who he would prefer to succeed Mr Brown, he said:"We are not there yet. It is very difficult to change a Labour leader before an election. When — or if — the time comes, I think it has to be David Miliband because he has shown maturity about the leadership and he withstood the pressure to stand last year against Gordon."

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