A row over "disgusting" e-mails containing unfounded claims about the personal lives of top Tories is convulsing Westminster.
Conservatives have called on Prime Minister Gordon Brown to publicly apologise, after one of his top advisers was found to have sent the e-mails - from Downing Street - to former spin doctor Derek Draper.
Mr Brown's close adviser, Damian McBride, has resigned and Mr Draper's proposed blog - on which the unfounded stories would have been published - never appeared.
The story broke after blogger Paul Staines revealed the existence of the e-mails on his Guido Fawkes site.
BBC News looks at the key figures involved:
DAMIAN MCBRIDE, EX-DOWNING STREET SPECIAL ADVISER
Mr McBride's decision to send Derek Draper scurrilous stories for his proposed Red Rag blog is not the first time he has been accused of risking all for a cheap headline.
A special adviser to Mr Brown since 2005, the Cambridge-educated civil servant, now 35, lost his job dealing with the media on a day-to-day basis last year after the resignation of former Transport Secretary Ruth Kelly was leaked to journalists.
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
Senior Labour figures felt the timing of the leak had detracted from the prime minister's party conference speech.
Mr McBride's special adviser status meant he had been allowed to give partisan - and sometimes strident - political briefings to journalists and he earned the nickname "McPoison".
He also gained a reputation for his tirades delivered via text message to reporters whose stories he disliked.
Unlike his predecessors in Downing Street, Mr McBride had never worked as a journalist, but is said to have first impressed Gordon Brown with his handling of the 2000 fuel protests while a Treasury official.
He was made the department's head of communications three years later and when Mr Brown moved into Number 10, he took Mr McBride with him.
Up until the smear scandal Mr McBride was responsible for the prime minister's strategy and planning - a key role with close access to the prime minister and other decision makers.
Now he has paid the ultimate political price - banishment from Downing Street itself - and few journalists are mourning his departure.
GORDON BROWN, PRIME MINISTER
Following his widely heralded success at uniting world leaders at the G20 summit, the e-mail smear row has provided Mr Brown with an unwelcome "back-to-earth" moment.
The row is said to have irreparably damaged the prime minister's contention that he operates via a "moral compass" and that he hates government "spin".
I am ready to take whatever action is necessary to improve our political system
This is because, although no-one seriously suggests that the prime minister knew about the specific content of the e-mails, critics say Mr Brown must have known about, and approved of, author Damian McBride's "style".
Journalists who have dealt with Mr McBride and other Gordon Brown advisers, like former spin-doctor Charlie Whelan, say the aborted smear strategy bore the hallmarks of the way Mr Brown's team has dealt with his enemies in the past.
They say Mr Brown's "attack dogs" are not afraid to brief against ministers or MPs seen as disloyal, and have bullied journalists who have written unsympathetic stories.
The prime minister, critics say, is not only damaged by guilt-by-association with Mr McBride, but must also answer for a long-standing practice of employing advisers known to use underhand tactics.
For his part, Mr Brown has written to the head of the civil service, Sir Gus O'Donnell to say "no minister and no political adviser other than the person involved" had knowledge of Mr McBride's emails."
He added: "Any activity such as this that affects the reputation of our politics is a matter of great regret to me.
"I am ready to take whatever action is necessary to improve our political system.
"I think you will agree that all of us in public life have a responsibility to ensure that those we employ and who are in involved in our parties observe the highest standards."
'E-MINISTER' TOM WATSON
The civil service minister, and key Gordon Brown ally in the Downing Street "war room", has kept his head down as the e-mail smear row erupted around him.
He has said the first he knew about the contents of the e-mails was when he read about them in the Sunday newspapers.
And apart from "categorically denying" weekend reports that he was copied in on the e-mails, a Cabinet Office spokesman said Mr Watson was unlikely to comment further.
DIGITAL ENGAGEMENT MINISTER
The first I was aware of the e-mail conversation that led to Damian McBride's resignation was when these were made known to Downing Street by national newspapers
Tom Watson MP
But the Conservatives continue to make much of reports that Mr Watson and e-mail author Damian McBride shared the same office in Downing Street.
The Cabinet Office spokesman confirmed that Mr Watson and Mr McBride did have desks in the same Downing Street war-room office, where strategy is planned.
"Whether they sit next to each other, or at the same time, I would not like to say," said the spokesman.
Conservatives also point to Mr Watson's own blog which tells of his special interest in "the digital world and social media".
They have called on Mr Brown's Minister for Digital Engagement to make it clear that while he may have been unaware of the content of the e-mails, he was also ignorant of plans to set up a new Labour-friendly blog site.
Before the current scandal erupted, Mr Watson was best known as the junior minister who resigned, before openly calling on Tony Blair to leave office.
Mr Watson's current post in Downing Street is widely seen as a reward for his loyalty to his friend and boss, Gordon Brown.
'SMEAR VICTIMS': GEORGE AND FRANCES OSBORNE, DAVID CAMERON, NADINE DORRIES MP
Mr Brown was forced into hand-writing regretful letters to the intended victims of the smear campaign.
The prime minister was prompted to act once the unfounded allegations - described as "disgusting" by one of his own ministers - became widely known.
Without going into detail, the stories that might have appeared on the proposed Labour-friendly blog are said to have included false rumours about the private lives of Conservative MPs, including Tory leader David Cameron.
David Cameron is furious about this... Gordon Brown owes an apology
Mr Cameron is said to be "furious" about the smear attempt and has called on Gordon Brown to apologise - something Mr Brown reportedly stopped short of in his letter.
But generating the most outrage, and not only among Tories, is an unfounded smear about the wife of shadow chancellor George Osborne.
Frances Osborne has now approached the Press Complaints Commission to report newspapers who repeated the false allegations in their Sunday editions.
The attempt to smear the relative of a political enemy is seen as a particularly underhand tactic - even by seasoned political observers.
Mrs Osborne's husband George is also the subject of a vicious and unfounded slur, as is Tory MP Nadine Dorries.
Ms Dorries, who previously attracted headlines for an unsuccessful attempt to reduce the time limit for abortions, condemned the attempt to smear her.
The Conservative MP for Mid Bedfordshire is now said to have consulted her lawyers about a possible libel action because, she says, the allegations about her are completely untrue.
She told the BBC that the e-mails were "a matter of great regret", and accused Mr Brown's office of attaining "a new moral low".
The e-mails also contained accusations that an unnamed Tory MP was promoting his partner's business interests in the Commons.
DEREK DRAPER, EDITOR OF LABOURLIST BLOG
A former aide to Lord Mandelson, ex-journalist and political lobbyist Derek Draper is no stranger to controversy.
The 41-year-old, who described himself as coming "from a loving but poor working-class background" but confessed to a love of champagne, was a key cog in the New Labour machine which propelled Tony Blair to power.
Are we really going to judge people for having silly ideas, even if they then put them in e-mails to mates?
He says his blog exists "purely to make mischief at the expense of politicians" and for his own "gratification", attacking politicians of all colours and in both Houses of Parliament.
When the site won an award from the Guardian newspaper, Mr Staines refused to accept the validity of its online poll and portrayed the paper as "trying to feed vampirically off the buzz and energy of the Blogosphere for whatever edgy cachet it has".
Since 2004, Guido's stock-in-trade is a mixture of tip-offs from Westminster insiders and humorous commentary.
In the wake of Mr McBride's departure, a gleeful post appeared on the blog. It read: "Mission Accomplished - McBride fired."
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