Cabinet ministers who want to become Labour's deputy leader should resign to enable a "genuine debate", a contender from outside the government says.
Mr Cruddas said rivals were playing "smoke and mirrors"
Dagenham MP Jon Cruddas accused rivals of playing "smoke and mirrors" and taking part in a "nodding-dog routine".
Instead, they "should all walk out", rather than staying in Cabinet while trying "to reinvent themselves as more radical", he told the New Statesman.
Several MPs have declared they want to succeed John Prescott as deputy leader.
Among them are Education Secretary Alan Johnson, Development Secretary Hilary Benn and Northern Ireland Secretary Peter Hain.
Constitutional Affairs Minister Harriet Harman has also declared, with Labour chairman Hazel Blears and Commons leader Jack Straw expected to do so.
Mr Prescott will leave his job later this year, when Tony Blair quits as prime minister.
Earlier this month, Mr Hain told the New Statesman that US President George W Bush's administration was the "most right-wing'' in living memory.
He added that it had "failed to provide a coherent international policy [and had] failed with the American electorate, who kicked it into touch".
The remarks were widely interpreted as an appeal to Labour's grassroots, many of whom are unhappy about the Iraq war.
Ms Harman, when interviewed by the magazine, commented on the row over whether Catholic adoption agencies should be able to opt out of gay discrimination rules.
She said: "You can either be against discrimination or you can allow for it. You can't be a little bit against discrimination."
Again, this was interpreted to be an appeal to party members angry that some ministers reportedly favoured a compromise.
However, Mr Cruddas said Labour needed an honest discussion on its future, which would not be possible if deputy leadership contenders stayed in government posts.
He added: "They should all walk out and we should all have a genuine debate, rather than all this briefing, leaking and playing both sides: in the Cabinet and simultaneously out of the Cabinet .
"They're playing smoke and mirrors to find themselves.
"After 10 years of doing the nodding-dog routine, they try to reinvent themselves as more radical."
Mr Cruddas has said the Labour deputy leadership should be separated from the deputy premiership.
The role should involve being "the voice of the party to the government", he added.
The former adviser to Mr Blair is thought to have strong support among trade unionists. He has been MP for Dagenham since 2001.