Labour MPs have no right to override the wishes of the party's membership on policy, a close ally of Jeremy Corbyn has said.
Former London mayor Ken Livingstone said Mr Corbyn had inherited a parliamentary party which was "well to the right" of the membership, and made clear his belief that MPs should bow to the wishes of activists on the direction taken by Labour.
This week's reshuffle had removed a "disaffected little group of old uber-Blairites" who had been engaged in a "wave of back-stabbing" designed to undermine the leader, he said.
Mr Livingstone's comments came as Mr Corbyn completed his shake-up of Labour's front bench by appointing a number of MPs to roles outside the shadow cabinet.
The much-heralded changes - dubbed a "revenge reshuffle" by critics - saw prominent MPs Pat McFadden and Michael Dugher sacked for alleged "disloyalty", while Kevan Jones, Jonathan Reynolds and Stephen Doughty resigned in response.
Pro-Trident Maria Eagle was replaced as shadow defence secretary by Emily Thornberry, who shares the leader's opposition to renewal of the UK's nuclear deterrent.
New Labour grandee Lord Mandelson was among a string of senior figures to warn that shifting the Opposition back to the policy of unilateral disarmament ditched in the 1980s would leave it "even further away from any prospect of winning a general election".
But shadow chancellor John McDonnell dismissed the trio who walked out as being from "a narrow right-wing clique" who refused to "respect" the strong mandate granted Mr Corbyn by members and supporters in September's leadership election.
And Corbyn loyalist Diane Abbott infuriated Mr Reynolds by referring to them as "former special advisers", sparking him to brand her a "total sell-out" for sending her child to a private school.
Mr Livingstone told BBC2's Daily Politics: "Diane was responding to this wave of back-stabbing by this disaffected little group of old uber-Blairites.
"What we have got to remember is Jeremy has inherited a Parliamentary Labour Party well to the right of the membership. That is because during the four general elections under Blair and Brown, local Labour parties weren't allowed to choose the candidate they wanted, they had to select from a list approved by the party bureaucracy.
"People who were critical of American foreign policy or wanted to crack down on the tax avoidance of big corporations never got onto the list.
"What these MPs can't now do is say `We have got a right to override the wishes of the party membership'."
Mr Livingstone said he agreed that former Europe spokesman Mr McFadden had been disloyal in a statement on the causes of Islamist terrorism.
"A lot of people like Pat McFadden who were central to Tony Blair's government have never come to terms with the fact that invading Iraq was a disaster," said Mr Livingstone. "It led to a million people - almost all of them innocent civilians, men, women and children - being killed.
"They can't ever come to terms with it when people like myself or Jeremy say having interventions and overthrowing governments and trying to control the oil in the Middle East is a big factor in fuelling terrorism."
Among the new appointments to the Labour frontbench are a trio of female MPs first elected to Parliament in last year's general election - Kate Hollern (Blackburn), Jo Stevens (Cardiff Central) and Angela Rayner (Ashton-under-Lyne).
Ms Hollern fills the vacancy left in the defence team by Mr Jones's departure, while Ms Rayner joins the work and pensions team following Emily Thornberry's promotion from employment spokeswoman to shadow defence secretary. Ms Stevens takes a post in Labour's justice team.
Middlesbrough MP Andy McDonald - elected in 2012 - takes a transport brief following the resignation of Mr Reynolds, and long-serving Leeds North East MP Fabian Hamilton, who has been in the Commons since 1997, goes to the foreign affairs team after Mr Doughty's departure.
Also appointed to the front bench as an education spokeswoman is Darlington MP Jenny Chapman, part of the 2010 intake.