LONDON, England (CNN) -- A key aide to British Prime Minister Gordon Brown has resigned after e-mails reportedly smearing top political opponents were leaked, British media said Sunday.
Senior politicians such as UK opposition leader David Cameron were reportedly smeared in the e-mails.
The e-mails, which made a number of innuendo-laden suggestions about the private lives of politicians, including Conservative Party leader David Cameron, ended up in the hands of a well known political blogger, it was reported Saturday.
According to The Observer, Damian McBride, a special adviser to Brown, discussed setting up a Web site to publish "scurrilous allegations about opponents" with former Labour party adviser Derek Draper.
Stories proposed by McBride and Draper in their exchanges included false rumors that Cameron had an embarrassing medical condition and that shadow finance minister George Osbourne once took drugs with a prostitute -- an allegation he has flatly denied -- The Observer said.
In another embarrassing security leak for the British government the messages ended up with Paul Staines, who writes under the name "Guido Fawkes."
The opposition Conservative party urged the prime minister to explain how the allegations came to be sent from an official e-mail account, the BBC said. The British broadcaster quoted senior Conservative lawmaker Chris Grayling as saying "this is an exceptionally serious matter and he needs to explain immediately what happened."
On Saturday, a Downing Street spokesman said the messages were "juvenile and inappropriate," but added that "neither the prime minister nor anybody else in Downing Street, except the author, knew anything about any of these private e-mails."
McBride was removed from his post dealing with the media following the resignation of former Transport minister Ruth Kelly in September last year. He remained with the government in a different role.
The latest security breach follows the resignation last week of a senior anti-terror policeman, after he was photographed arriving at Downing Street holding a document revealing details of a secret terror raid.