A judge says Britain has been stunned by revelations about child sexual abuse, and the true scale of the crime may be worse than official estimates that one in 20 children has been a victim.

Justice Lowell Goddard opened a public inquiry into decades of abuse on Thursday, vowing that "no one, no matter how apparently powerful, will be allowed to obstruct our inquiries."

In the past few years revelations of abuse have implicated everyone from taxi drivers to entertainers, clergy and senior politicians. There have been claims that police failed to investigate allegations of abuse for decades.

Goddard, a New Zealand judge, was appointed earlier this year to head an inquiry into how public agencies — including government bodies, police, hospitals, churches and the BBC — handled child-abuse allegations.