We were not plotting to dump Blair, insists Brown’s close ally

The papers, obtained by the Daily Telegraph, show how Mr Balls and current Labour leader Ed Miliband were assigned roles by Mr Brown in an operation to ensure his succession as PM.

Whitehall officials were yesterday investigating whether the leak amounted to a breach of Government secrecy.

The papers – including hand-written memos from Mr Brown and letters from Mr Blair to his then chancellor – were last seen in Mr Balls’s office at the Department for Children. They appear to have gone missing from boxes of private possessions passed on to his House of Commons office following Labour’s election defeat in 2010.

Following a complaint from Mr Balls, the Cabinet Office said officials were 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 said: “The last time I saw them was when they were on my desk in the department. I don’t know how they were taken and got to the Telegraph.”

He dismissed as “false and mendacious” claims that the papers showed there had been a plot by Mr Brown’s supporters to unseat Mr Blair.

“The idea that there was a plot or a coup is untrue and not justified by these papers,” said Mr Balls.

His role had been to try to “hold things together” at a turbulent time. Acknowledging that the relationship between Labour’s most powerful figures “could have been better handled”, he insisted that the party had changed since the days of “tensions and rows” between Blairites and Brownites. “There are important lessons to learn, people want to know that the Labour Party has learned them,” said Mr Balls. “We have, 100 per cent.”

Meanwhile, Mr Miliband vowed the current generation of Labour chiefs would not repeat the “mistakes” of Mr Blair and Mr Brown.

“Everything wasn’t always perfect about their relationship,” said Mr Miliband.

“We are not going to make those mistakes. Frankly this is ancient history – that era is over and we are looking forward to the future.”

But Conservative Party deputy chairman Michael Fallon said that the papers showed that Mr Balls and Mr Miliband could not be trusted.

“While Britain’s debt doubled, welfare spending spiralled out of control and education standards fell, they were obsessing about getting rid of the elected prime minister and putting Gordon Brown into position,” said Mr Fallon.

“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.”

Cabinet minister Michael Gove, who took over from Mr Balls at the renamed Department for Education last May, appeared confident that his officials were not to blame for the leak.

A source close to the Education Secretary said: “Like with (former Haringey social services chief) Sharon Shoesmith, Ed Balls is pathetically trying to blame officials.

“He should ask his best friend Damian McBride how these things get leaked.”

The reference to Mr McBride, a former Brown aide thought to be behind negative briefings against rivals, suggests those around Mr Gove suspect the leak to be a result of internal Labour feuding.