Britain's tabloids are braced for more damaging celebrity testimony this week at a public inquiry that has turned the tables on Fleet Street and could lead to major changes in the regulation of the press. Singer Charlotte Church and Alastair Campbell, the former spin doctor of ex-prime minister Tony Blair, are among those due to give evidence during the second week of hearings at the Leveson inquiry into press ethics. But already the probe -- launched by Prime Minister David Cameron in July amid the furore over the phone-hacking scandal at the Rupert Murdoch-owned News of the World tabloid -- has sharply divided opinion. During the dramatic first week of testimony, "Harry Potter" author J.K. Rowling and actors Hugh Grant and Sienna Miller launched an onslaught against the newspapers they accused of ruining their lives. Perhaps the most poignant testimony came from ordinary crime victims, including the parents of murdered teen Milly Dowler who were given false hope that she was alive when the News of the World hacked her voicemails. Comedian Steve Coogan, who also testified to the inquiry, which is led by senior judge Brian Leveson, said it had been a "watershed" week. "The Leveson inquiry has acted in the same way as genuine public interest journalism," Coogan told the BBC on Saturday. But Graham Foulkes, whose phone was hacked after his son died in the July 7, 2005 bombings on London's transport system, said he would not be taking part in the inquiry because it had been "hijacked" by celebrities. "Leveson was set up around phone hacking but it has become a celebrity circus," Foulkes, whose son David died in the attacks, told The Times newspaper -- itself owned by Murdoch. And a leading lawyer, Paul McBride, also criticised the attention on the inquiry. It had heard little evidence of actual lawbreaking, he said. Police time would be better focused on unsolved murders, he added. "I watched the Leveson inquiry, with endless celebrities babbling away about how their lives have been ruined by media intrusion when often they have paid millions of pounds to PR consultants to get their names into the paper," he said. On Monday Church, a former child star who entertained Britain's Queen Elizabeth II, pope John Paul II and US president Bill Clinton, is due to give evidence about the alleged phone hacking of her family. Campbell appears on Wednesday and is expected to focus on links between the press and politicians -- which came under spotlight this summer as Cameron's former spokesman Andy Coulson was himself once an editor of the News of the World.Current and former journalists will also testify, including Nick Davies of the Guardian, the British newspaper that helped break the phone-hacking story. During the first week, a repeated complaint by witnesses was the inadequacy of the Press Complaints Commission, the current self-regulatory body for British newspapers. Several also complained that tabloids took a bitter revenge against people who stood up to them. But there has been little consensus from the British media on the inquiry, as different newspapers, broadcasters and bloggers all have their own axes to grind. Britain's "quality papers" such as the Guardian, Daily Telegraph, Times and Independent have jumped on the testimony of victims as proof that their tabloid cousins were out of control. Knowing that they are in the line of fire, the tabloids have generally taken a much quieter line, although the Daily Mail branded Grant "mendacious" for claiming that the Mail on Sunday newspaper had hacked his phone. The inquiry is expected to report in late 2012.