Gordon Brown has launched an all-out attack on News International accusing it of using "disgusting" methods to gain access to personal information.
The former prime minister also alleged the newspaper giant had links to the "criminal underworld".
And he accused The Sunday Times of gaining access to his personal bank and legal files when he was chancellor.
News International said it would investigate Mr Brown' s allegations and wanted to see all the information.
Mr Brown remained silent about alleged abuses of media power during his time in office - but he has been prompted to speak out by fresh claims in The Guardian that he had been targeted by News International newspapers.
In an interview with BBC News, the Labour MP said he was "in tears" when he was told that the Sun had details of his son Fraser's medical condition - he has cystic fibrosis - as he had wanted the information to be kept private.
"Sarah and I were incredibly upset about it," he said.
He said he did not know how the newspaper had got access to the details: "The fact is, it did appear and it did appear in the Sun newspaper."
But News International said they had conducted an inquiry into that story and said the story had come from someone who had a relative with cystic fibrosis, who had volunteered the information to highlight the illness. That person had provided a written affidavit to confirm it, the company said.
A spokesman said: "We are able to assure the Brown family that we did not access the medical records of their son, nor did we commission anyone to do so." He added that the company was not aware of any complaints that Mr Brown had made about the story at the time.
In separate allegations, it is claimed personal details were obtained for a front-page Sunday Times report that Mr Brown had bought a flat owned by Robert Maxwell at a "knock-down price".
Mr Brown told the BBC the story had been "completely wrong" but the company had been "trying to prove a point" and had aimed to bring him down as chancellor.
He also alleged the newspaper had got access to his building society account and legal files: "I'm genuinely shocked to find this happened because of the links with known criminals who were undertaking this activity, hired by investigators who were working with the Sunday Times."
He added: "If I, with all the protection and all the defences and all the security that a chancellor of the exchequer or a prime minister has, is so vulnerable to unscrupulous tactics, unlawful tactics ... what about the ordinary citizen?
"What about the person - like the family of Milly Dowler - who were in the most desperate of circumstances ... and then they find that they are totally defenceless in this moment of greatest grief from people who are employing these ruthless tactics?"
He said he had complained to the Sunday Times at the time, through his lawyers - but had not complained to the police because he had only recently "found out about the links between the Sunday Times and what I would call elements of the criminal underworld ... to do work which, if you like, is the most disgusting of work".
The Guardian newspaper has reported that a conman working for the Sunday Times was used to get access to Mr Brown's files from his London lawyers - the conman was later jailed for fraud in relation to a different matter.
Mr Brown said he had got his information from investigations done by journalists "and not myself".
He dismissed claims that he had done little to tackle alleged abuses of press power, claiming that in his final months in office he had wanted a judicial inquiry but said at the time "very few people who accepted this was the right thing to do".
He also claimed that he had "stood up" to News International's commercial ambitions when he thought they were against the public interest.
A spokesman for News International said: "We note the allegations made concerning the reporting of matters relating to Gordon Brown. So that we can investigate these matters further, we ask that all information concerning these allegations is provided to us."
Prime Minister David Cameron said it appeared Mr Brown had been victim to an "appalling invasion of privacy" and pledged that the government would get "to the bottom of what is clearly an appalling mess", through a police investigation and a judge-led inquiry.
He said his heart "went out to Gordon and Sarah Brown" about the story that emerged about their son: "To have your children' privacy invaded in that way, and I know this myself, particularly when your child isn't well, is completely unacceptable and heart breaking for the family concerned."
Health officials in Scotland said they would examine any evidence that patient confidentiality may have been breached at the hospital where Fraser Brown was born - the Edinburgh Royal Infirmary.
NHS Lothian said it took the issue "very seriously" and it promised a full investigation if there was any evidence of wrongdoing by staff.
Another News International title, the News of the World, was last week accused of using a private investigator to listen to the mobile phone messages of murdered schoolgirl Milly Dowler.
Labour leader Ed Miliband met the Dowler family on Tuesday to discuss the allegations and the planned inquiry. He is due to meet Mr Cameron and Deputy PM Nick Clegg at 1830 BST to discuss the phone hacking inquiry.
Mr Miliband added: "I think it's terrible what happened to Gordon. I think it's disgusting, and I think it just adds to the long list of outrages that we've seen practised by certain newspapers and I think it reinforces the need for comprehensive action to be taken."