The allegations of child sex abuse at public institutions that have emerged so far are just the "tip of the iceberg", Theresa May has warned.
The Home Secretary said it was crucial for society to "get to the truth" of what happened in the 1970s and 1980s.
Meanwhile, Scotland Yard chief Sir Bernard Hogan-Howe insisted police are taking claims "seriously" and promised there will be no cover-up.
The Government is still seeking a chairman for its wide-ranging inquiry into the handling of paedophile activity by public bodies after two candidates quit over their links to senior figures from the period.
Among the latest allegations are that police may have helped cover up the murder of an eight-year-old boy by a Westminster paedophile ring.
But May told the BBC's Andrew Marr show she was determined that the issues would be fully investigated.
"How was it that in the past, but continuing today, the very institutions of the state that should be protecting children were not doing so?" she said.
"Why was it that these abuses were able to take place and that nobody was brought to justice as a result of that?
"We must as a society, I believe, get to the truth of that and because I think what we're seeing is frankly - what we've already seen revealed - is only the tip of the iceberg on this issue."
The Metropolitan Police commissioner said dozens of detectives were investigating historic Westminster child abuse allegations and there was no question of anything being covered up while he was in post.
"We have got 40 detectives looking into these relatively new claims," he said.
"There are a series of claims over a relatively long period of time and not all of them are linked, although in the public's imagination they may be.
"We have now had more recently this discussion or these claims about murder and, of course, that makes it even more serious."
Shadow home secretary Yvette Cooper said: "The latest revelations on historical child abuse are alarming and the Home Secretary is right that this is likely to be the tip of the iceberg.
"It is important the inquiry gets under way and that action is taken swiftly to make the system better now so we can protect our children and take what they say about anyone seriously.
"But the Home Secretary needs to also take action over the National Crime Agency who are only investigating the tip of the iceberg of current cases too."