Former News of the World newspaper editor and Prime Minister David Cameron's director of communications, Andy Coulson, leaves number 10 Downing Street in London January 21, 2011. The British prime minister's media chief quit on Friday over allegations of phone hacking at the newspaper he used to edit, a move that could embarrass the prime minister and complicate News Corp's bid to buy BSkyB. REUTERS/Suzanne Plunkett (BRITAIN - Tags: POLITICS MEDIA CRIME LAW)