Jeremy Corbyn leads in nominations, makes plea for unity after split warnings

However, the shadow health secretary was picked as the best leader by members of the public and Labour voters in an opinion poll.

As the contest to succeed Ed Miliband appeared to signal a shift to the left in Labour ranks, former shadow chancellor Ed Balls issued a warning that the party must not allow itself to appear "anti-business".

Revealing his reservations about Mr Miliband's flagship energy price freeze policy, Mr Balls said the former leader had given the impression power companies were "the bad guys".

"It was no secret that I thought from the very beginning that Ed needed to position himself better with business," Mr Balls told The Daily Telegraph. "If you allow yourself to be anti-business, or anti-bank or anti-energy company, people think, 'Hang on a second, you have to work with these people if you want to govern'."

Mr Burnham used an interview in The Guardian to sound an "alarm bell" about comments from Communication Workers Union deputy general secretary Dave Ward, who described Blairites in the party as a "virus" to which Mr Corbyn was the antidote.

"There is a factionalism that is bubbling under here which, to his credit, Jeremy has not (endorsed)," said the shadow health secretary "There is a risk, though, of a split if people talk in that provocative way."

Referring to the period of bitter divisions which led to the formation of the breakaway Social Democratic Party, Mr Burnham added: "There are dangers here, there are some echoes of the early 80s. Those should ring loud warnings, alarm bells ... Labour needs to reflect on this, and not go down that path."

In an apparent criticism of Mr Miliband, Mr Burnham said Labour was "hungry for something different" after being fed a "diet of thin, meagre gruel of gimmicky policies". His own election manifesto will next week set out "the most radical Labour vision since the post-war government", he said.

In a statement, Mr Corbyn called for a "debate embracing all members from all parts of the party" during the postal ballot, which opens on August 14 and leads to the election of a new leader on September 12.

"The leadership election should be conducted with one thought in mind: our objective is to be a united party focused on winning the general election and campaigning across the country, day in day out," said the Islington North MP, who has become the bookies' favourite in recent days after entering the contest as the rank outsider.

Warning against predictions of splits, Mr Corbyn said: "When the dust has settled, we will still all be Labour. Let's conduct our debate on the basis of comradeship and unity in action against the damaging agenda of the Tory Party."

Mr Corbyn had a clear lead in CLP nominations with 152 to Mr Burnham's 111, Ms Cooper's 106 and Ms Kendall's 18. Supporting nominations have no weight in the ballot and members are free to ignore their constituency party's choice, but they offer an insight into the preferences of the most active party members.

In the deputy leadership race, Tom Watson secured an overwhelming lead in CLP nominations with 174, more than twice second-placed Stella Creasy's 77, and well ahead of Caroline Flint on 64, Angela Eagle on 32 and Ben Bradshaw on 20.

Among 1,001 members of the public questioned by market research company Research Now, Mr Burnham was picked as best Labour leader by 30% of those who expressed an opinion, ahead of 24% for Mr Corbyn and Ms Cooper and 21% for Ms Kendall. Among those who backed Labour in May, Mr Burnham was on 36% to Mr Corbyn's 28%, with Ms Cooper (20%) and Ms Kendall (16%) trailing.

A spokesman for the Burnham campaign said: "Andy is clearly the candidate to win back lost voters to Labour and unite the party at the same time."

But a Cooper-supporting MP dismissed the polling as "fantasy figures".