ED Balls, the Shadow Chancellor, yesterday denied he was involved in a plot to oust Tony Blair from office, after Whitehall officials launched an inquiry into the leaking of private papers that revealed new details of infighting in the previous Labour Government.

The typed and scrawled memos and lists, obtained by the Daily Telegraph, belonging to Mr Balls revealed how Gordon Brown assigned roles to Mr Balls and fellow Treasury aide at the time Ed Miliband, in a bid to ensure the then chancellor succeeded Tony Blair as prime minister. It was dubbed Project Volvo because Mr Brown was regarded as “dour” and “robust”, like the car.

The papers were last seen in Mr Balls’s office at the Department for Children and appear to have gone missing from boxes of private possessions passed to his Commons office after Labour’s election defeat last year.

Following a complaint from the Shadow Chancellor, the Cabinet Office said officials were now looking into whether the papers had been “in the possession of any Government department” and if so, whether there had been “any breaches of document security within Government”.

Mr Balls dismissed as “false and mendacious” claims the papers showed there had been a plot by Mr Brown’s supporters to unseat Mr Blair, saying: “The idea that there was a plot or a coup is untrue and not justified by these papers.”

However, he admitted discussions on the transition from Mr Blair to Mr Brown had begun before the 2005 General Election and, at times, were “fraught” and “difficult”. He said it was “deeply frustrating” to have to rebut the conspiracy claims once again, and was a distraction from the current economic crisis and an attempt to “take people back to those times”. He asked: “Obviously the question is: who thinks it is in their interests to take my papers and pass them to the Daily Telegraph?”

Mr Miliband has vowed not to return to the “mistakes” of the Blair/Brown era, adding: “Frankly, this is ancient history; that era is over and we are looking forward to the future.”

However, the leaking of the papers provided Conservative HQ with political ammunition.

Michael Fallon, the Tories’ deputy chairman, said: “Instead of owning up to their role in a dysfunctional government and coming up with a credible plan to deal with the problems facing Britain, they are starting to plot against each other. They can never be trusted with government again.”

A source close to Michael Gove, the Education Secretary, suggested the minister was confident his officials would not be blamed for the leak, but again used the incident to launch a political attack. “Ed Balls is pathetically trying to blame officials. He should ask his best friend Damian McBride how these things get leaked.”

Mr McBride, a former Brown aide, was thought to have been behind negative briefings against rivals in the so-called “smeargate” scandal.

The leaked papers show discussions about the Labour succession were under way within Mr Brown’s inner circle shortly after the party’s 2005 election victory. A lengthy memo from Mr Brown accuses Mr Blair of “self-promotion” and says the then PM was happy to see the media frame Labour’s internal wrangling as a battle between himself as a reformist and the then chancellor as a block on reform.

In response, Mr Brown wrote: “If we are to renew Labour, we must be as rigorous and as brutal as we were in the creation of New Labour.”

Memos gave Mr Balls the task of bringing together a “small group” of Brown loyalists, including Mr Miliband and Douglas Alexander, the Shadow Foreign Secretary, to prepare for a leadership election.

Yesterday, Mr Alexander, on the stump for the Inverclyde by-election, denied the leaked papers would damage Mr Miliband’s leadership.