Brown told to clean up Downing Street or lose election

This comes after the departure of his aide, Damian McBride, who proposed a smear campaign against David Cameron, the Opposition Conservative leader.

As a furious Mr Cameron demanded a personal apology from the Prime Minister, a senior Labour figure warned the party had suffered "reputational damage".

Mr McBride, a senior Brown aide dating back to the Prime Minister's time as Chancellor of the Exchequer, resigned on Saturday after a political blogger, Guido Fawkes, uncovered a series of emails outlining plans for a smear campaign against senior Tories.

The Prime Minister's adviser proposed articles for a new Labour-supporting website, to be called Red Rag, to "destabilise" the Tories. Mr McBride's ideas, which he emailed to Derek Draper, the former adviser to Lord Mandelson who runs the LabourList website, suggested a series of innuendo-laden and unsubstantiated stories.

These ranged from spreading gossip that Mr Cameron had suffered an embarrassing medical condition to starting rumours that George Osborne, the shadow chancellor, who was once pictured with a prostitute, was haunted by further embarrassing pictures from his past which had yet to emerge.

Senior Labour figures are planning to tell Mr Brown this week that such behaviour cannot be repeated if Labour is to win the election, expected next year.

One key Labour figure said: "Damian McBride and his cohorts belong to Gordon's past and not his future. They are not fit to serve any prime minister and certainly not in the modern communications age. Labour has suffered reputational damage."

Mr Brown had no idea that Mr McBride, who initially worked for him as communications director at the Treasury before becoming a political media adviser, had written the emails.

"Gordon had no idea what Damian was up to," one minister said. "Gordon is appalled."

But Mr Cameron has rejected Downing Street's defence: that the emails were a "juvenile" prank by Mr McBride which signified nothing because the smear campaign - and the Red Rag website - were dropped.

A Tory spokeswoman said Mr Cameron was furious and said that Mr Brown was embroiled because he was familiar with Mr McBride's modus operandi.

William Hague, the Tory spokesman on foreign affairs, said: "Fair-minded people across politics, and people of no political persuasion at all, will see it as a deeply depressing sign of the priorities of Downing Street and of the British Government at the moment.

"That is why it is entirely fair to ask what we are asking for: an apology from the Prime Minister, a thorough investigation into what has happened, an assurance that these people will not work for the Government again."

A Downing Street spokesman added: "Neither the Prime Minister, nor anybody else in Downing Street, had knowledge of these emails."

Guardian News & Media