One in 20 children in England and Wales may have been sexually abused, says a judge brought in from New Zealand to chair a British inquiry into accusations of institutional paedophilia during the 1980s.
Interior minister Theresa May announced the inquiry last summer in the wake of press revelations - confirmed by ministers - that files relating to 114 claims of sexual abuse against children between 1979 and 1999 had disappeared.
The probe will examine claims of sexual abuse among politicians and within public institutions.
The investigation was delayed by the resignation of two previous chairs, most notably Elizabeth Butler-Sloss.
Her brother Michael Havers, who was attorney general in the 1980s, is accused of trying to prevent a former lawmaker from going public with sexual abuse allegations.
Instead, May looked overseas to ensure there were no suggestions that the chair had links to British establishment figures and New Zealander Lowell Goddard was eventually given the role.
The judge said on Thursday that the probe "provides an opportunity to expose past failures of institutions to protect children".
"The task ahead of us is daunting," she added, saying there were suggestions that as many as five percent of children in England and Wales were victims of abuse.
"The sexual abuse of children over successive generations has left permanent scars, not only on the victims, but on society as a whole," she said.
British police opened their own investigation in March into complaints that police had covered up evidence of a high-level paedophile ring between 1970 and 2000.
Another police investigation is already underway to examine the actual claims of abuse during those years.
The inquiry follows the sensational revelations surrounding the late Jimmy Savile, a well-known BBC presenter who was exposed as one of the country's worst child-sex offenders after his death in 2011.