Gordon Brown told yesterday how he and his wife Sarah were left "in tears" when The Sun discovered that their four-month-old son had cystic fibrosis.
But claims that the newspaper had obtained the information by accessing Fraser Brown's medical records were challenged by Rupert Murdoch's News International (NI) last night.
An NI 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. The story The Sun ran about their son originated from a member of the public whose family has also experienced cystic fibrosis.
"He came to The Sun with this information voluntarily because he wanted to highlight the cause of those afflicted by the disease. The individual has provided a written affidavit confirming this."
Charlotte Harris, a media lawyer with the solicitors Mishcon de Reya, said that even if the Sun had received the information from another parent, it had been "highly insensitive and callous" to contact the Brown family and demand confirmation of their son's condition in the manner in Mr Brown described, saying the newspaper "seeks to justify a gross breach of privacy by blaming the victim."
In an interview with the BBC yesterday, Mr Brown accused NI of conspiring with a criminal underworld to obtain stories and of repeated "abuses of power". He claimed the Sunday Times had obtained his bank details and said he had evidence that private investigators had blagged personal information from his lawyers and that people obtained details from his building society on six occasions by posing as him.
A spokesperson for The Sunday Times denied the newspaper had broken the law to obtain the information, and claimed it had "pursued this story in the public interest".
Mr Brown said he believed he was targeted because he "stood up to News International" and took decisions that went against their interests. In his emotional interview, the former Prime Minister told how he felt when The Sun approached him with the story about Fraser.
"Sarah and I were incredibly upset about it. I've not questioned how it appeared, I've not made any allegations about how it appeared, I've not made any claims about how it appeared, but the fact is it did appear and it did appear in The Sun."
The NHS is investigating how medical information about the Brown family was leaked.