LONDON (CNN) -- Celebrated "Harry Potter" author J.K. Rowling has said she feels "duped and angry" over British Prime Minister David Cameron's response to a major inquiry into phone hacking and other abuses by the press.

Rowling was one of hundreds of witnesses to testify to the Leveson Inquiry into media standards and ethics, set up in the wake of a phone-hacking scandal at Rupert Murdoch's News of the World tabloid.

The judge who led the inquiry, Lord Justice Leveson, released his long-awaited report Thursday, in which he recommended an independent regulator be set up by the press, which would be backed by new laws to make sure it meets certain standards.

Cameron, of the Conservative Party, supported Brian Leveson's call for an independent regulator -- but said he was not convinced that legislation is needed to underpin the new body.

Rowling expressed her disappointment in the prime minister's decision in a statement posted Friday on the website of Hacked Off, a group campaigning for media reform.

"Having taken David Cameron's assurances in good faith at the outset of the inquiry he set up, I am merely one among many who feel duped and angry in its wake," she wrote. 

"I thought long and hard about the possible consequences to my family of giving evidence and finally decided to do so because I have made every possible attempt to protect my children's privacy under the present system, and failed."

Rowling is concerned that members of the public who do not have the money to fight the press in the courts, over such abuses as invasion of privacy or libel, will continue to suffer.

"Those who have suffered the worst, most painful and least justifiable kinds of mistreatment at the hands of the press, people who have become newsworthy because of the press's own errors or through unspeakable private tragedy, are those least likely to be able to defend themselves or to seek proper redress," she said.

"Without statutory underpinning Leveson's recommendations will not work. We will be left with yet another voluntary system from which the press can walk away."

The author also questioned why millions of pounds had been spent on the inquiry if the prime minister did not intend to follow its recommendations -- and urged people to sign a petition set up by Hacked Off if they agreed.

The group has already collected more than 50,000 signatures from members of the public in support of the full implementation of Leveson's recommendations.

Cameron's decision caused immediate divisions within the country's coalition government.

Deputy Prime Minister Nick Clegg, who leads the Liberal Democrats in the coalition, said he believes new legislation is needed to ensure the regulator's long-term independence.

Ed Miliband, leader of the opposition Labour Party, also said he favors full implementation of Leveson's recommendations, including the new legislation.

In his report, Leveson said that he had no desire to jeopardize the freedom of the press, which he acknowledged plays a "vital" role in safeguarding the public interest, but that changes are needed to tackle abuses.

The British press has ignored its own code of conduct on "far too many occasions over the last decade," causing "real hardship" and sometimes wreaking "havoc with the lives of innocent people," Leveson said.

The independent inquiry was first announced by Cameron in July 2011 in response to public outrage over a newspaper phone-hacking scandal.

The trigger was the allegation that in 2002, the voice mail of a missing 13-year-old girl, Milly Dowler, had been hacked by an investigator working for the News of the World before she was found murdered. The furor led to the closure of the newspaper, run by News International, a subsidiary of the Murdoch-owned News Corp.

CNN's Per Nyberg contributed to this report.

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