Journalists from across Rupert Murdoch's stable of newspapers repeatedly tried to hack into the phone of Gordon Brown when he was British finance minister and prime minister, the Guardian and Independent newspapers reported on their websites on Monday.
The Independent said Brown would make a statement on the matter imminently. The Guardian said News International reporters had repeatedly targeted Brown, attempting to access his voicemail and obtaining information from his bank account, his legal file as well as his family's medical records.
Until now, allegations of illegal reporting practices have centered on the News of the World, Murdoch's mass-selling Sunday paper. The new reports alleged that there had been similar malpractice at sister papers in the News International stable.
Brown's office could not immediately be reached for comment despite repeated calls and emails.
News International, part of Murdoch's News Corp group, said in a statement that it noted the allegations made concerning Gordon Brown. So that we can investigate matters further we ask that all information concerning these allegations is provided to us, it said.
The Guardian said it had uncovered evidence that Brown had been targeted over a period of more than 10 years, both as finance minister and as prime minister.
It also reported that a building society had unearthed evidence suggesting that a blagger acting for the Sunday Times on six occasions posed as Brown and gained details from his account.
It also said Brown's London lawyers had been tricked into handing over details from his file by a conman who, the Guardian said, worked for the Sunday Times.
In addition, and perhaps most damaging, a Guardian investigation found that details from Brown's infant son's medical records may have been obtained by the mass-market Sun.
The paper revealed in 2006 that Brown's son Fraser has cystic fibrosis.
(Writing by Stefano Ambrogi; Editing by Kevin Liffey)