Sun newspaper denies accessing medical records of Brown's son

In a dramatic intervention, Mr Brown said: "I can't think of any way that the medical condition of a child can be put into the public arena legitimately unless the doctor makes a statement or the family makes a statement."

However, News International - which publishes The Sun - said this evening: "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 this afternoon to a lawyer confirming this."

The statement went on: "On receipt of the information, The Sun approached Mr Brown and discussed with his colleagues how best to present it.

"Those colleagues provided quotes which were used in the published piece which indicated his consent to it. We believe that the article was written sensitively and appropriately.

"We are not aware of Mr Brown, nor any of his colleagues to whom we spoke, making any complaint about it at the time.

"The publication of the story and the further responsible, sympathetic and informative coverage The Sun continued to give to the disease resulted in renewed interest for those affected by it. Donations to the Cystic Fibrosis Trust nearly doubled over the next year.

"We continue to inquire into other allegations made by Mr Brown, and implore him to provide details to us so we can establish the facts."

In his interview today, Mr Brown described how when he was chancellor the newspaper's then editor Rebekah Brooks - now News International chief executive - rang to say she knew that four-month-old Fraser had cystic fibrosis.

"Sarah and I were incredibly upset about it," the former prime minister said.

"We are thinking about his long-term future, we are thinking about our family, but there is nothing that you can do about it - you are in public life and this story appears, you don't know how it's appeared.

"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 newspaper."

Mr Brown also made a series of other allegations about News International newspapers. He said there was evidence that private investigators "broke into" his own legal files by blagging personal information from his lawyers and that, on six occasions, people obtained details from his building society by posing as him.

"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," Mr Brown told the BBC.

"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.

"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."

He went on: "I find it quite incredible that a supposedly reputable organisation made its money, produced its commercial results, at the expense of ordinary people by using known criminals. That is now what has got to be investigated."

Mr Brown said News International had sought to abuse its power to pursue a political agenda on issues like the future of the BBC and the "neutering" of broadcasting regulator Ofcom.

He insisted that he resisted the company while he was prime minister and even sought to set up a judicial inquiry into its activities, but faced resistance from the police, British Home Office and Cabinet Office.

"When the record of my time as prime minister is looked at - and all the papers will be there for people to see - they will show that we stood up to News International, that we refused to support their commercial ambitions when we thought they were against the public interest," he said.

"It is partly because we stood up to News International and party because we refused to go along with some of their commercial proposals that were purely in the interests of their company that News International didn't find that they could support the Labour Party at the last election."

A spokeswoman for The Sunday Times denied it had broken any laws or used criminals when investigating the purchase of a flat by Mr Brown.

"We pursued this story in the public interest," the spokeswoman said. "We were told that Mr Brown had bought a flat cheaper than any normal valuation and that he obtained it through a company in which Geoffrey Robinson, a close ally, had been a director.

"We had reasonable grounds to investigate this matter and followed the Press Complaints Commission (PCC) code on using subterfuge.

"We believe no law was broken in the process of this investigation, and contrary to Mr Brown's assertion, no criminal was used and the story was published giving all sides a fair hearing.

"We also note that Allen & Overy, the law firm, have denied they handed over any details about the purchase of the property and had nothing to do with it."