The Conservative party has demanded a personal apology from British prime minister Gordon Brown after details emerged of smear stories that forced one of his closest aides to quit.
Damian McBride resigned after admitting sending "juvenile and inappropriate" emails from his Downing Street account to former spin doctor Derek Draper.
In the private missives, the two men discussed setting up an "attack blog" called Red Rag that would have spread unfounded gossip about Conservative opponents.
According to the
Sunday Times, the mooted stories — which are all vehemently denied — included spreading rumours about the health of shadow chancellor George Osborne's wife, challenging David Cameron to reveal details of an "embarrassing illness", and accusing a Tory MP of promoting his partner's business interests in the Commons.
Shadow home secretary Chris Grayling branded the stories "blatant lies cooked up in Downing Street", and asked who else had been aware the talks were taking place.
"Mr Brown hasn't even had the decency to apologise. His statement this afternoon was unacceptable," he said
"This is an exceptionally serious matter and he needs to explain immediately what happened and how such defamatory comments came to be issued from Downing street."
Mid Bedfordshire MP Nadine Dorries confirmed she was among four Tories featured in the emails, and called for the prime minister to say sorry.
"I would also like to know how Gordon Brown would feel if CCHQ wrote such disgusting lies about his wife, Sarah Brown," she wrote on her blog.
Pressure had been growing on Mr McBride all day after the existence of the emails was confirmed. The discussions took place in January, and were somehow leaked to right-wing blogger Paul Staines.
Former home secretary Charles Clarke — one of Labour's "big beasts" waded in by accusing Mr McBride of "shaming" the party and urging his removal.
The special adviser's resignation was finally announced just before 5pm, with Mr Brown insisting there was "no place" in politics for such material.
Mr McBride, who has been with Mr Brown since his Treasury days, said in a statement that he was "shocked and appalled" at the way the emails had been used, and regretted any embarrassment caused to the government.
A Downing Street spokesman said: "Neither the prime minister, nor anybody else in Downing St, had knowledge of these emails.
"It is the prime minister's view that there is no place in politics for the dissemination or publication of material of this kind, which is why it is right that Mr McBride and Mr Draper took the decision not to publish this material and regrettable that others are choosing to do so."
Mr McBride added: "I have already apologised for the inappropriate and juvenile content of my emails, and the offence they have caused, but I did not want these stories in the public domain — it is because Paul Staines has put them there, and I am sickened that he has done so.
"However, we all know that when a backroom adviser becomes the story, their position becomes untenable, so I have willingly offered my resignation."
Mr McBride was the prime minister's political spokesman until last October, when he was shifted to become head of strategic planning at Number 10 amid criticism of his handling of Ruth Kelly's resignation.
Mr Staines — who has had a long-running spat with Mr McBride — welcomed the departure, and rejected criticism that he had caused the problem by obtaining and revealing the nature of the material.
"It raises questions about how Labour operates," he told Sky News. "This kind of smearing, pouring poison in journalists' ears. I think Damian was using it to destroy Labour politicians, never mind opponents.
"That (tactic) is gone now. That was the 1990s."
Mr Draper said Mr McBride was paying "a high price" for material that he had not chosen to publish.
"They were never published on a website," he said. "I do not think they would ever have been published on a website... that kind of thing is not right."
He went on: "You have to wonder just for having an idea, even though it was a silly idea, whether someone deserves to lose their job. It is a very heavy price to pay for something that never actually happened."
Cabinet Office minister Liam Byrne dismissed Mr McBride's smear suggestions as "scribble", and said he had now done the "honourable thing".
"Once Mr McBride had scribbled this stuff and exchanged it with (Derek Draper) I think he concluded that actually either Mr Draper's website and indeed the public at large didn't need this stuff, didn't deserve it, it was not something that should have been waved in the public's face, and indeed belonged in the bin.
"That was the decision that he took, so it is actually through the decisions of others who are determined that it should come into the public domain that we have heard about this news."
PA