Police are investigating an estimated 600 new allegations of phone hacking at Rupert Murdoch's now defunct News of the World, a British newspaper says.
Citing unnamed sources, the Guardian newspaper said new hacking information had been obtained from the phone records of an "insider" who is now being lined up as a prosecution witness.
The news comes at a sensitive time for the British media, with a divisive parliamentary vote on how to regulate Britain's famously aggressive newspapers due to be held on Monday, Reuters reports.
Prime Minister David Cameron is pushing for a form of self-regulation, while the opposition and his Liberal Democrat coalition partners want any new regulatory framework to be backed by new legislation.
Scores of celebrities, politicians, crime victims and others have sued or demanded compensation from News International - the British newspaper arm of Mr Murdoch's News Corp media empire - since hacking revelations emerged two years ago.
Britons were shocked to learn that News of the World journalists had hacked the phone of a murdered school girl, but the practice is now known to have been more extensive.
Allegations of phone hacking have since spread to another newspaper, the Sunday Mirror, and police arrested four former editors from the tabloid on Thursday.
The Guardian said the same insider behind new allegations of phone hacking at the News of the World also led to the arrests at the Sunday Mirror.
On Friday, British media reported that Richard Wallace, a former editor of the Daily Mirror, the Sunday Mirror's sister paper, was questioned by police but was not arrested.