Former prime minister Gordon Brown accused News International newspapers today of accessing private information about himself and his family.
He said he and his wife were "in tears" after being told by the Sun that it was going to publish a story about their son's cystic fibrosis.
And 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."
He went on: "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."
Mr Brown said he could not think of any legitimate means by which the Sun could have got hold of details of his four-month-old son Fraser's cystic fibrosis in 2006.
"They will have to explain themselves," he told the BBC. "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.
"I make no claims, but the fact of the matter is that I had my bank accounts broken into, I had my lawyers' files effectively blagged, my tax returns went missing at one point.
"I don't know how all this happened, but I do know one thing: that in two of those instances there is absolute proof that News International was involved in hiring people to get this information."
News International sources were quoted last night 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."
But Mr Brown's broadside ensured that the hacking story remained firmly in the spotlight.
He spoke out as one of Britain's top policemen, Metropolitan Police assistant commissioner John Yates, told the Commons Home Affairs Select Committee that the News of the World "failed to co-operate" with police inquiries into phone hacking until the start of this year.
Mr Yates, the Met's head of counter-terrorism, also expressed regret at his 2009 ruling that there was no need to reopen the phone-hacking investigation and he said he was "99% certain" his phone had been hacked.
Mr Brown said he tried to secure a judicial inquiry into the conduct of News International while he was in power, but faced resistance from the police, Home Office and Cabinet Office.
He accused the company of seeking to abuse its power for political gain over issues such as the future of the BBC and the "neutering" of broadcasting regulator Ofcom, but insisted that as prime minister he had resisted it.
And he added: "Of course, the abuse of their power for political gain is something that is going to have to be looked at. Any inquiry that is going to be set up is going to have to look at how News International attempted to abuse political power for political gain."
Speaking during a visit to Wales, Prime Minister David Cameron said Mr Brown's claims were "yet another example of an appalling invasion of privacy".
"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," Mr Cameron said.
He insisted that the police would "find the culprits and make sure they are punished", while the promised judge-led inquiry would find out "what was going on at these newspapers".
"This Government won't rest until we have got to the bottom of what is clearly an appalling mess," he said.
Mr Yates faced difficult questioning by MPs, insisting he had always told the truth to the Home Affairs Select Committee.
He said: "I can assure you all that I have never lied and all the information that I've provided to this committee has been given in good faith.
"It is a matter of great concern that, for whatever reason, the News of the World appears to have failed to co-operate in the way that we now know they should have with the relevant police inquiries up until January of this year.
"They have only recently supplied information and evidence that would clearly have had a significant impact on the decisions that I took in 2009 had it been provided to us."
Mr Yates also strongly denied allegations in the New York Times that he was put under pressure not to investigate phone hacking at the News of the World because of fears that the Sunday tabloid would publish details about his personal life.
"I categorically state that was not the case to each and every one of you. I think it's despicable, I think it's cowardly," he told the MPs.
Mr Yates said he had "never, ever, ever" received payment from journalists for information but admitted it was "highly probable" that some of his officers did.
Asked by committee chairman Keith Vaz whether he had offered to stand down from his job, the senior officer said: "No, I haven't offered to resign.
"And if you're suggesting that I should resign for what News of the World has done and my very small part in it, I think that's probably unfair."
Labour MP Mr Vaz told Mr Yates at the end of the session that the committee found his evidence "unconvincing".
He told him: "There are more questions to be asked about what happened when you conducted this review.
"So you may well be hearing from us again. Please do not regard this as an end of the matter."
