* Former Murdoch editors accused of phone-hacking offence
* Coulson quit PM Cameron media role over scandal
* Denies affair with Brooks meant they shared stories
By Michael Holden and Kate Holton
LONDON, April 14 (Reuters) - David Cameron's former media chief Andy Coulson told a London court on Monday he had not spoken to the British prime minister since his arrest, and admitted his affair with Rebekah Brooks when working for Rupert Murdoch tabloids was wrong.
Coulson and Brooks, the ex-boss of News Corp.'s British newspaper arm, are on trial accused of charges linked to phone-hacking. Prosecutors have suggested that their affair played a key role in their involvement in criminal offences.
Both edited the now defunct News of the World newspaper at the heart of a phone-hacking scandal which erupted in 2011 and sent shockwaves through Britain's political establishment, not least because of Coulson's close links to Cameron.
Prosecutors have told the jury at London's Old Bailey court that Brooks and Coulson shared details of stories obtained from phone-hacking when Coulson was editor of the News of the World and Brooks was editing its sister daily the Sun.
However, on his first day in the witness box during the 5 1/2 month trial, Coulson echoed Brooks's evidence that their affair, which began in 1998 and ran until 2004, had been intermittent and had not interfered with their work.
"What I want to say is that it was not by any means continual," said Coulson, who arrived at court holding hands with his wife, whom he married in 2000.
"I don't want to minimise it or excuse it, it was wrong, it shouldn't have happened and I take my full share of responsibility for the pain it has caused other people, not least my wife".
Asked if they had shared exclusive stories or sensitive information because of their relationship, he replied: "No that wouldn't happen."
Coulson left the mass-selling News of the World in 2007, when its royal editor and a private detective Glenn Mulcaire, who worked for the paper, were convicted of hacking the phones of royal aides.
He said at the time that he had not known about the hacking but felt he should stand down due to the seriousness of the offence.
Shortly afterwards Coulson, who left school at 18 to join his local paper, went on to work for Cameron when he was leader of the opposition Conservatives, and moved with him into Downing Street after the May 2010 election when he became prime minister.
Coulson, 46, quit the role in January 2011 when the phone-hacking scandal re-emerged as a major issue.
"Not long after, my family and I spent a weekend with him, I think that was in the Spring, it may have been in the April, after I left," said Coulson.
"I haven't spoken to him since," added Coulson, who was first arrested in July 2011, causing huge embarrassment for Cameron.
Looking composed and speaking confidently, he told the court he had not heard Mulcaire's name before his arrest. Nor had he played a part in the decision to reverse plans to cut Mulcaire's 105,000 pound ($175,700) annual contract in 2005.
"It's not an area of the News of the World I was particularly interested in," he said, adding he never used private detectives himself when building his career as a show business reporter.
Prosecutors have said he must have known what such a large amount of money was being spent on, but Coulson said in overall terms at the paper, the sum was not that great.
"I don't want to be dismissive of 105,000 pounds but the reality is it was not a lot of money. We paid double that to the astrologer," he said, adding they also spent 22,000 pounds on flowers and alcohol.
Coulson and Brooks deny conspiracy to illegally intercept voicemails on mobile phones and authorising illegal payments to public officials.
Brooks is also accused of conspiracy to pervert the course of justice. Five others are also on trial and they all deny the charges. The trial continues. (Editing by Angus MacSwan)