Kinnock: Ed Miliband is not in danger as Labour leader
Ed Miliband's leadership of the Labour Party is "not in danger", one of his predecessors, Lord Kinnock, has said.
The former leader said the threat to Mr Miliband was "not substantial" and attacked the "cowardice" of anonymous critics after further reports of unhappy Labour MPs.
But shadow cabinet minister Caroline Flint admitted some of her colleagues were having "jitters".
Mr Miliband says claims of a challenge to his position are "nonsense".
Speaking on BBC Radio 4's The World This Weekend, Lord Kinnock acknowledged the headlines in the Sunday newspapers - including a report in the Observer that 20 shadow ministers are ready to call on him to quit - were "serious".
But he said: "The so-called threat is certainly not substantial - not only because the sources... of the threat are common in their anonymity and cowardice and, as far as I can see, tendency towards political suicide - but because there is not real substance in what they are saying."
Lord Kinnock praised Mr Miliband's "proven courage" and said he was "approachable".
He added: "The portrayal of him remote, cerebral, and weird, if you like - this word that's really doing the rounds - that's a total contrast to the man as he really is."
A YouGov poll in the Sunday Times has suggested only 34% of people who voted Labour at the last general election believed Mr Miliband was up to the job of prime minister, compared with 51% a month ago.
It follows earlier reports that some backbenchers wanted him to resign and that his leadership was questioned at a meeting of Labour MPs from north-west England.
However, no Labour MPs have publicly called for him to step down and a string of high-profile figures have given interviews defending him.
Ms Flint, the shadow energy secretary, told the BBC's Sunday Politics: "Look, some of my colleagues are having jitters and part of that is that we've always said that this is not a done deal, this election, this is going to be hard-fought, and we said that from 2010 and Ed has been saying it since he was elected our leader.
"We have to fight for the right to represent the country in Westminster."
Labour backbencher Simon Danczuk told BBC One's Sunday Politics Mr Miliband would lead the party into the election, but added: "The numbers show us he's not popular. That's the reality."
Speaking on Sky News, former Labour MP Andrew Mackinlay said Mr Miliband should step down. But former London Mayor Ken Livingstone predicted he would become "the most significant prime minister since Margaret Thatcher".
Former Home Secretary Alan Johnson, who has been talked of as a potential Labour leader, told the Sunday Express a leadership challenge would be "political suicide".
He said: "I ruled out a leadership bid in 2010 when there was a leadership election. There is no leadership election now.
"I am very supportive of Ed and I think he is doing a good job."
Labour is keen to move the focus away from debate about the leadership and Mr Miliband is expected to make a speech warning that threats of the UK leaving the European Union are a "clear and present danger".
He will tell the CBI on Monday that an EU exit would "close us off from the world" and risk jobs.
Mr Miliband is expected to tell business leaders the UK is "ever more isolated from its partners", urging closer working with other members to reform the EU budget.
"Leaving the single market and stepping away from a trading block that strengthens Britain's ability to work with the new economies, like Brazil, India and China, would be a disaster for our country," he is expected to say.