Labour Party MPs attacking Ed Miliband are having a "bout of political insanity", according to former Home Secretary David Blunkett.
The Sheffield MP, who is standing down at the 2015 General Election after 28 years in Parliament, criticised backbenchers who have reportedly cast doubts over Miliband's leadership.
"When you are standing on the edge of a cliff, it is unwise to believe that by jumping you will suddenly learn to fly," Blunkett told The Guardian.
"This bout of political insanity has to stop. If anyone thought that a leadership election concluding in January following a continuing bout of bloodletting would do anything to improve our prospects, I suggest they take an emergency course in citizenship politics."
The 67-year-old, who served under former Prime Minister Tony Blair in various ministerial roles, made the comments amid reports that Labour MPs are split over Miliband's leadership and backbenchers are circulating a letter calling on him to resign.
The Shadow Chancellor, Ed Balls, said the rumours were "nonsense" and claimed that Labour would "stay united" behind Miliband.
"I think this is all nonsense, to be honest. I've no idea about any of this," Balls told BBC News.
"All I know is that everybody in the Labour party, from Miliband down, is focused on tackling the cost of living crisis, building an economy which works for working people, reforming Europe but not walking away, getting tough and fair controls on immigration, saving our national health service – that's what Labour's for.
"It's the Conservative Party which are riven and divided and defecting, left, right and centre. Labour will stay united."
The latest YouGov poll for The Sun gives the party a one point leader over the Conservatives (33% vs 32%) ahead of the 2015 General Election next may.
A separate survey from YouGov for LBC Radio found that almost half (49%) of UK voters think that the Labour Party would be better off at the election if they ditched Miliband as leader.