Tessa Jowell sought an assurance from Tony Blair that he had made no deal with Rupert Murdoch on media regulation when she was appointed culture secretary, the Leveson Inquiry heard on Monday.
Jowell said the then-prime minister promised her that there was "no prior agreement" with the media baron on his government's reforms to cross-media ownership rules.
Last week Blair's former chief spin-doctor Alastair Campbell revealed that Jowell had wanted to be sure she would not be constrained by a secret agreement between Blair and Murdoch.
"She wanted to be sure, as it were, she wasn't going into a policy area where a conclusion had been reached," he said. "Tony Blair was able to give her that assurance."
Jowell told the inquiry on Monday that Blair's instincts to deregulate were even stronger than hers, but insisted that was not driven by "any particular media company".
She said she spoke to the prime minister within days of her appointment as culture secretary in June 2001.
"I asked him whether any deal had been done with Rupert Murdoch on the reform of cross media ownership," she said.
"He gave me an absolute assurance, which I completely accepted, that there had been no prior agreement.
"So I had no constraint on the conclusion I might reach."
Jowell said she had urged Blair not to see the interested parties so that her decision-making would not be undermined by direct lobbying of Number 10.
"I wanted to make sure that the meetings I had, the proposals I developed, were not being undermined by representations being made directly to Number 10, and the prime minister understood the risks of that," she said.
She said that she "invited lobbying" on the reforms by a wide range of media companies and other interested parties, and said she had more than 150 meetings.
"I don't think there was more lobbying from News International than other media groups," she said.
The inquiry heard that Jowell had a number of meetings with News International chief Les Hinton over the following year, but insisted there was no "negotiation" with the company over possible media reforms.
"It wasn't a negotiation. They came to see me to tell me what their view was, as did scores of other media interests," she said.
On Blair's stance on the reforms, the former culture secretary said: "His instincts were probably not motivated by any particular media company. His instincts were more deregulatory than mine."
Asked whether there was any discussion about how the deregulation might affect Labour's relationship with Murdoch, she said: "No. There was no discussion of that."
Jowell was also asked whether her approach to policy was influenced by Blair's opinions. "Of course," she replied. "He was the prime minister".