Former minister Michael Meacher has said a poll demonstrates that Labour members feel ignored by the leadership.
Michael Meacher says the poll shows Labour members' dissatisfaction
His comments come as more than 1,000 Labour members and activists meet in London to discuss renewing the party.
Ministers, trade unionists and campaign leaders are addressing a conference, organised by left-wing group Compass.
Mr Meacher said: "We have lost half of our members and four million voters since 1997. This is a very serious problem."
The YouGov poll suggests 71% of current and former Labour members want Tony Blair to step down as prime minister before autumn 2007.
"They said the leadership did not trust its members sufficiently to involve them fully in party decisions and policy-making," Mr Meacher said.
"Even when the Government does consult, it gives no indication whatsoever that it listens to what is said or modifies its policies.
"It's that that gets up the noses of lots of members.
Compass has named its conference after the late Robin Cook.
The group is headed by former adviser to Gordon Brown, Neal Lawson, and recently pressed for a timetable for Mr Blair's departure from Downing Street.
That prompted cabinet minister John Reid to call Compass an "old Labour lobby group" while Mr Blair said its policies were the surest route to opposition.
But a range of ministers are addressing the conference, including Labour chairman Hazel Blears, International Development Secretary Hilary Benn and chief Brownite ally and minister Ed Balls.
Compass plans to issue a manifesto at the end of the year following a number of what it calls renewal roadshows - which its organisers say will try to assess the political moment and the political times.
But the conference also follows the frenzy of speculation over the Labour leadership, with Commons Leader Jack Straw predicting Mr Blair will leave "well before" the next election.
Mr Meacher, who heads the independent Labour Commission, was due to present the findings of the new YouGov opinion poll to the conference.
It suggests 71% of them want Mr Blair to go before next year's Labour conference and more than a third, 37%, want him to quit in the next three months.
But the poll suggests a majority do not think Deputy Prime Minister John Prescott should stand down until Mr Blair departs.
Mr Meacher will focus on poll findings which show a majority of those questioned want Labour's manifesto to be put to a vote of members before general elections.
And 64% of those questioned said they thought the party leadership did not trust members to get involved in drawing up policies.
Mr Meacher said: "The biggest single issue in Britain today is the lack of accountability of political power.
"The checks and balances requiring the prime minister to consult and listen have been all but eliminated."
He said the Labour Commission would now prepare proposals on how to meet the demands. Labour has highlighted its efforts to try to improve links with party members in recent years with a series of consultation events.
YouGov quizzed 670 Labour Party members and 704 lapsed members online between 1 June and 6 June.