Cameron answers questions over judgement regarding Coulson

In a letter written four years ago - and made public on Tuesday (August 16) - in an appeal against his dismissal from the tabloid, former royal reporter Clive Goodman said the practice of hacking was openly discussed until the then-editor Coulson banned any reference to it."This practice was widely discussed in the daily editorial conference, until explicit reference to it was banned by the Editor," the Goodman letter said, published as part of a parliamentary investigation into hacking.

Coulson, who has repeatedly denied all knowledge of the practice, went on to become the official spokesman for Cameron, a move which took the affair into the political arena and forced the government to turn on Rupert Murdoch after years of courting his favour.

"If I'd known then all the things I know now then obviously I would've taken different decisions," said Cameron.

Allegations of widespread hacking at News Corp's British newspaper arm, and in particular reports that journalists had used investigators to hack in to the voicemails of murder victims, sparked an uproar in Britain that dominated global headlines for almost the whole of July.

It forced the company to close the 168-year-old News of the World, drop its most important acquisition in decades -- the $12 billion purchase of BSkyB -- and accept the resignation of two of its most senior newspaper executives.

For Prime Minister Cameron, the damage is by association. He repeatedly defended Coulson after hiring him as his spokesman and denied accusations that the appointment was designed to secure Murdoch's support.

He has said he will apologise if it transpires that Coulson lied over what he knew about hacking.