British Prime Minister David Cameron has begun looking for a new media chief to replace Andy Coulson after he quit over a tabloid phone-hacking row, in a test for the nine-month-old government. A senior Cameron aide told The Guardian in London today after Coulson quit , bowing to pressure over what he knew about hacking at the News of the World when he was its editor.The dramatic development also renewed questions about practises at the Sunday tabloid, commentators said, at a crucial time for its owner, Rupert Murdoch's News Corporation, which is trying to expand its media holdings in Britain.Coulson had been under growing pressure about what he knew about the activities of the NOTW's royal editor and a private investigator who were jailed in January 2007 for hacking voicemails of Princes William and Harry.