Former prime minister Gordon Brown has accused the Sunday Times of using criminal activity to intrude into his private family life.
He spoke out after it emerged that "blaggers" had been used to access personal files, including his bank account.
Mr Brown said he and his wife were "in tears" after being told by the Sun that it was going to publish the story about his son's cystic fibrosis, gleaned from medical files.
He told the BBC: "I think that what happened pretty early on in government is that the Sunday Times appear to have got access to my building society account, they got access to my legal files, there is some question mark about what happened to other files - documentation, tax and everything else.
"I'm shocked, I'm genuinely shocked, to find that this happened because of their links with criminals, known criminals, who were undertaking this activity, hired by investigators with the Sunday Times."
News International sources were quoted as saying they were "comfortable" that stories reported by the Sun about Mr Brown's children were obtained via legitimate means. In a statement, News International said it noted the allegations about Mr Brown, adding: "So that we can investigate these matters further, we ask that all information concerning these allegations is provided to us."
Mr Brown added: "I just can't understand this - if I, with all the protection and all the defences and all the security that a chancellor of the Exchequer or a prime minister, am so vulnerable to unscrupulous tactics, to unlawful tactics, methods that have been used in the way we have found, what about the ordinary citizen?
"What about the person, like the family of Milly Dowler, who are in the most desperate of circumstances, the most difficult occasions in their lives, in huge grief and then they find that they are totally defenceless in this moment of greatest grief from people who are employing these ruthless tactics with links to known criminals."
The Prime Minister said Mr Brown's claims were "yet another example of an appalling invasion of privacy". "This Government won't rest until we have got to the bottom of what is clearly an appalling mess," David Cameron said.
"My heart goes out to Gordon and Sarah Brown because to have your children's privacy invaded in that way - and I know that myself particularly - when your child isn't well, is completely unacceptable and heart-breaking for the family concerned," he said.