LONDON -- Britain has been stunned by revelations about child sexual abuse, a judge said Thursday, warning that the true scale of the crime has been underestimated and one in 20 children may have been a victim.

Justice Lowell Goddard opened a wide-ranging public inquiry into decades of abuse in Britain's schools, hospitals and other institutions, vowing that "no one, no matter how apparently powerful, will be allowed to obstruct our inquiries."

A dam of official silence around child abuse in Britain began to break after the 2011 death of entertainer Jimmy Savile, when dozens came forward to say he had abused them. Subsequent revelations have implicated taxi drivers, entertainers, clergy, senior politicians and others. There have also been claims that police failed to investigate allegations of abuse for decades.

Earlier this year Goddard, a judge from New Zealand, was appointed to investigate how public agencies -- including government bodies, police, hospitals, the army, churches and the BBC -- handled allegations.

Goddard said abuse has been systematically under-reported by police and "the true picture may be even worse than the current figures indicate." She said estimates from a childcare charity suggest one U.K. child in every 20 has been sexually abused; some academics believe the level is higher.

The inquiry plans to release its final report in 2020 but Goddard promised annual updates starting next year. Victims will be able to testify anonymously and former civil servants will not be charged if they disclose official wrongdoing.

Goddard has told police and other institutions not to destroy any records relating to child care.

The abuse claims reach so deeply into British society that finding someone to lead the inquiry was problematic. Two previous chairwomen were appointed and then rejected because of their connections to the establishment.

While the inquiry doesn't have the power to find people guilty of crimes, Goddard said it will not hesitate to name abusers, regardless of their positions in society.