Cameron told to rein in special advisers over negative briefings

David Cameron has been officially reprimanded by the head of the civil service over the "unacceptable" behaviour of some of his special advisers.

Sir Gus O'Donnell wrote a strongly worded letter to the Prime Minister urging him to restrain Government aides accused of "smearing" the head of the Electoral Commission. He was said to have been furious after reading a newspaper report describing Jenny Watson, a former Audit Commission board member, as "incompetent"

The report, citing a Whitehall source, claimed Ms Watson was "milking the taxpayer" and predicted she would be sacked by Communities Secretary Eric Pickles in "a bonfire of the quangocrats".

Labour last night called for an inquiry to identify those responsible who, they said, should be sacked. The disclosure of the letter is damaging to Mr Cameron who had promised to draw a line under the anonymous – and often poisonous – briefings by Labour advisers during the previous government.

Gordon Brown's press spokesman Damian McBride was forced to resign after he was exposed plotting to smear senior Tories. Labour special adviser, Jo Moore, left Government after she sent an email suggesting that 11 September 2001 was a good day to "bury" bad news.

When the Conservatives came into power all their new special advisers – political aides to ministers – were warned by that if they leaked information to the press they would be fired.

But that diktat appears not to have extended to the Tories' enemies – much to the annoyance of the Cabinet Secretary. The letter from the Cabinet Secretary to the Prime Minister, which was leaked to the magazine PRWeek, is understood to have read: "You will have been aware of briefings to the media regarding Jenny Watson. This behaviour is unacceptable. I trust you will agree with me and take necessary action to make sure that people understand this will not be tolerated."

In response to a Freedom of Information request by PRWeek, the Cabinet Office confirmed that Sir Gus had written to the Prime Minister in late 2010 to discuss "the role, status or conduct of government special advisers". However, an official declined to provide the correspondence in question.

A spokesman for the Cabinet Office said: "We never comment on any advice the Cabinet Secretary might or might not have provided to the Prime Minister."

But a Downing Street insider who witnessed the episode unfolding told the magazine of mounting concern in Whitehall about the activities of some Tory special advisers. The source said: "The quotes about Jenny Watson were the final straw. [Sir] Gus was so concerned that he raised it with the PM a few days later, saying this is unacceptable behaviour and please reign in your spads [special advisers]."

Labour's Caroline Flint, shadow Communities and Local Government Secretary, said: "The head of the Civil Service would not have written to the Prime Minister without good cause. David Cameron and Eric Pickles must now come clean about whether or not advisers were responsible for these disgraceful negative briefings. If they were, then they should be sacked.

"Eric Pickles talks a lot about transparency, yet so far he has done all he can to avoid answering questions about the alleged conduct of his aides."

The quotes first appeared in The Times in September 2010. The newspaper reported that Mr Pickles was embarking on "a bonfire of the quangocrats", with Ms Watson top of his hit list. A Whitehall source told the paper: "She was begging Mr Pickles to stay on but we are not having someone who built their career on incompetence continuing to milk the taxpayer.

"She is not fit for the role. The Audit Commission has lost its way and the last thing we need is someone like her on board. She has no previous experience outside the public sector. We have had a bonfire of the quangos; now we are having a bonfire of the quangocrats."