Former home secretary Charles Clarke has said Labour is suffering from "debilitating" uncertainty about its policy direction.
In an article for the Labour magazine Progress, he said the party had wasted much of this Parliament and needed to show "a lucid sense of direction".
He told the BBC he was not blaming Gordon Brown as problems began in 2004.
But he said the PM needed to set out his approach to "tough problems" like Britain's role in the EU.
Mr Clarke said that once his close ally Tony Blair announced he would not contest another election in October 2004, questions about the party's leadership had dominated Labour.
'Inevitability of defeat'
He wrote that the party had wasted much of this Parliament and must show greater "clarity, decisiveness and a lucid sense of direction" and said the prime minister must do more than defend past achievements and launch more policy reviews.
And he said there was "absolutely no reason to surrender to the inevitability of defeat, as too many seem now to be doing".
Later he told BBC Radio 4's World at One programme it had not been an attack on Mr Brown, with whom he said he now had a "very cordial" relationship.
"I don't particularly criticise Gordon in this regard in fact most of the problems I am describing derive from the period where Tony Blair was leader," he said.
But he said many people who work with government - either business or public sector workers - needed to know what the government's policy approach was.
"Fundamentally people need to know where they stand and what our approach is going to be. I think that a general bottom-up review of everything after more than 10 years in office, is essentially not credible to people."
Mr Hain resigned from the cabinet to clear his name
He said difficult issues like reform of housing benefit or the relationship between local education authorities and trust schools had been "shied away from" because they were so difficult.
"Because there are conflicting views about these things, it's sometimes easier to push the decision away rather than take it. But I think we have to take those decisions."
Asked about other issues he said the decision not to pay the police and other public sector workers their pay award in full had been a "misjudgement" - as teachers had been treated differently.
And he said he was "absolutely astonished" when the news emerged that Labour had accepted £650,000 in proxy donations, and was "amazed" at other problems that arose out of the deputy leadership elections.
Peter Hain has resigned after it emerged he had not declared many donations to his campaign.
Mr Clarke said the prime minister was "more isolated" than Tony Blair was, as while Mr Blair had a separate deputy PM, party chairman and general secretary - Harriet Harman now held two of those roles and no general secretary had yet been appointed.
He said the party leadership team was not "as clear and strong as it needs to be", but may improve when a general secretary was appointed.
But he said he would back the government's controversial proposal to extend the period for which terrorism suspects could be held without charge and said the Conservatives, who oppose the plan, were being "very irresponsible".
The prime minister's spokesman said of Mr Clarke: "He has every right to make his comments.
"He is a distinguished former minister with much to offer public life."