Alan Johnson will not run for 'onerous' Labour leadership role Branding the role "onerous," Mr Johnson confirmed he would not be returning to the front line of politics "regardless of circumstances," and said he was convinced Mr Miliband could become Prime Minister. His denial comes amid looming doubts over Mr Miliband's future as leader, as rumours abound that party members may soon attempt to unseat him. At yesterday's CBI conference in London, Mr Miliband distanced himself from reports and said"you shouldn't believe everything you read in the papers." Mr Johnson, the MP for West Hull who stood down as shadow chancellor nearly three years ago, accused Labour of naval gazing and warned it could lose "precious months"" ahead of the May 2015 general election by arguing about the leadership. At the beginning of this parliament the Labour party lost precious months conducting an overlong leadership campaign that allowed the coalition government to develop its big fat lie about the global recession, while we in Labour examined our collective navel. The question of the leadership was settled then. It must not be re-opened," he wrote in the Guardian. Miliband will lead us into an election that I am convinced we can win. It was my decision to walk away from frontline politics, not Ed's. Read more: Miliband's problem is that he's too neurotically in touch Chuka Umunna accidentally calls Ed Miliband Dave Chuka shines; hangovers; and American fears Labour supporters do not believe Miliband is fit to be PM Offering Mr Miliand his fill support in the coming months, Mr Johnson continued:"He knows that while I won't return, I will do everything I can from the backbenches to put Labour into government, and Ed Miliband into 10 Downing Street. The position of Labour leader has been vacated twice during my time as a member of parliament. Both times I chose not to stand. I happen to think that a better person took this onerous role on each occasion. I have never stood for the leadership of my party - and for the avoidance of doubt, regardless of the circumstances, I never will. Shadow home secretary Yvette Cooper also dismissed suggestions that she was preparing for a leadership bid as "complete nonsense." "There was stuff in the papers that people have put there for their own reasons, but it just damages the Labour Party but it's just made up, it's not true," she told the BBC. Meanwhile, a letter signed by 100 Labour candidates - including many in key marginal and target seats - called for an end to the "campaign of briefing to destabilise Ed and his leadership." Published by the LabourList website, it said that Mr Miliband had "led our party to within striking distance of government" and that they were "proud to be led by a man that we know to be honest, sincere and decent. "We have watched in disappointment over recent days as an anonymous few have attempted to orchestrate a campaign of briefing to destabilise Ed and his leadership," the would-be MPs said. "It is a distraction from the real issues, damaging for our party and it has to stop," they added. Additional reporting PA