Gordon Brown has denied claims made by the former chief executive of News International, Rebekah Brooks, that he gave permission for The Sun to run a story about his infant son's illness.
Giving evidence to the inquiry on Monday morning under oath, the former prime minister said he and his wife had not been given a choice as to whether the tabloid revealed the information.
In November 2006 the tabloid made public the fact that Brown's four-month-old son Fraser had been diagnosed with cystic fibrosis.
In her evidence to the inquiry last month, Brooks said she only decided to run the story because she felt the Browns had given her permission.
Asked whether she had the "express permission" of the Brown's to publish the story she replied: "Absolutely".
"If the Brown's had asked me not to run it I wouldn't have done," she said. "Not only did they give me permission to run it it is the only way we would have put it in the public domain."
However asked by the inquiry today whether he or his wife had "absolutely" not given permission, Brown said there was "no question of implicit or explicit permission" given by him or his wife Sarah to the paper to run the story.
He told the inquiry that they wanted to "minimise the damage" done to his family and had initially wanted to put out a statement to all the press.
However this, he said, was deemed "unacceptable" by The Sun who told them unless they gave a statement exclusively to the paper it would in future not give him any warning about stories it planned to publish.
Brown also criticised The Sun for mounting personal attacks on him over his handling of the war in Afghanistan.
The former prime minister said the paper "descended into sensationalism" because it wanted to damage his premiership rather than engage in a serious debate about the conduct of the war.
In 2009 The Sun attacked Brown for misspelling a deceased soldier's name in a handwritten note sent to the family.
He said the paper made the story "not about an honest mistake, but about evil intentions".
Brown said the paper was wanted to simply "demonise" him and claimed that since Labour lost power in 2010 it has been "virtually silent" on the war in Afghanistan.
He also accused The Sun of "damaging our effort in Afghanistan" in the way it reported the war.
"Huge damange was done to the war effort by the suggestion we did not care about what was happening to the troops," he said.
Brown told Leveson that he did not believe The Sun had ever really supported the Labour Party and said it had tried to tried to "ruin" his first party conference as leader.
"They they ran a huge campaign on 'Broken Britain' that was simply an attack on the current government," he said.
And he said he was "not surprised at all" when the paper switched its formal support from Labour to the Conservatives in 2010.
"The act of deciding to go with the Conservatives had been planned over many many months," he said. "I never complained to The Sun about us losing their support."
Rupert Murdoch told the inquiry that Brown had declared "war" on News International after The Sun withdrew their support from the Labour party.
The News Corp boss said the then prime minister told him in a phone call: "well, your company has declared war on my government. And we have no alternative to make war on your company".
But Brown said the conversation did not happen and there was "no evidence" that it had.
"I did not call him, I had no reason to want to call him, and I would not have called him," he said.
Lord Mandelson told the Leveson inquiry during his evidence that Brown should should not have taken The Sun's switch of support from Labour to the Conservatives "so personally".
The former Labour business secretary said News International simply saw "greater commercial interest" in the election of a Conservative government than a Labour one.
"I'm afraid a Labour government coming to the end of 12 or 13 years of office had been buffeted by events and by changing electoral attitudes," he said.
Lord Mandelson added: "He [Brown] shouldn't have taken it so personally, this is politics.
"My view was shrug it off, don't dignify them with tears, crocodile or otherwise."
Brown also used his appearance infront of the Leveson inquiry to attack the Conservative Party for being too close to News International.
He said that while he and his wife had been friends with Rebekah Brooks this did not influence policy decisions made by his government.
"You can serve up dinner but you don't have to serve up BSkyB as part of the dinner," he said.
What The Other Witnesses Have SaidSuggest a correction
Jeremy Hunt: I Considered Quitting Over BSkyB Row
Rebekah Brooks: David Cameron Signed Off His Texts 'LOL'
DCMS Permanent Secretary Jonathan Stephens: Hunt Urged Cameron To Back News Corp Bid
Ken Clarke: The Press Is More Powerful Than Parliament
Michael Gove: Rupert Murdoch Is A 'Impressive And Significant' Man
Tony Blair: I Chose Not To Take On The Press