The cases of child abuse exposed so far are only the “tip of the iceberg” of the extent of sexual exploitation of young people, the Home Secretary Theresa May has warned.

Ms May spoke of her dismay over the number of abusers who have been able to operate with impunity both in the past and today.

She said it was impossible to assess whether the activities of a paedophile ring involving senior figures in public life were covered up in the 1980s, but insisted an independent inquiry into historical sex abuse would establish the full facts.

“It’s not possible to say whether there was a cover-up, that is why I think it is so important we have the inquiry so we get at the truth,” she told the Andrew Marr Show.

“There is a real issue here about 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. Why was it these abuses were able to take place and nobody was brought to justice as a result of that?”

Who could lead the abuse inquiry? Show all 6 1 /6 Who could lead the abuse inquiry? Who could lead the abuse inquiry? Brian Moore, 52 A former England rugby player and qualified solicitor who was sexually abused as a child by a teacher. Once s staunch Labour supporter, he now holds both left- and right-wing views Getty Who could lead the abuse inquiry? Alexis Jay A professor who specialises in social work, she is the independent chair of the Centre for Excellence for Looked After Children in Scotland (Celcis) and a Rotherham sex abuse scandal expert. She was appointed expert adviser to the child abuse inquiry in September PA Who could lead the abuse inquiry? Baroness Kennedy of The Shaws, 64 A formidable British barrister, broadcaster and Labour member of the Lords who has experience in cases of domestic and child abuse Rex Who could lead the abuse inquiry? Sir Alan Ward, 76 Retired and accomplished Court of Appeal judge with experience in family disputes, he helped Ian McEwan with his recent book on the Children Act PA Who could lead the abuse inquiry? Lady Justice Hallett, 64 Respected Court of Appeal judge with extensive criminal experience who was coroner of the 7/7 inquests. There might be hesitancy over losing a serving judge to an inquiry with an indefinite duration PA Who could lead the abuse inquiry? Lord Carlile of Berriew, 66 A Liberal Democrat peer who is one of Britain’s top legal experts, acting as the independent reviewer of terrorism legislation from 2005-11. He is known for not being afraid to speak out against the authorities Rex

She added: “We must, as a society... get to the truth of that and because I think we we’ve already seen revealed is the tip of the iceberg on this issue.”

Sir Bernard Hogan-Howe, the Metropolitan Police commissioner, pledged that the full truth of sex abuse claims – as well as a new allegation that a boy was murdered by paedophiles in the 1980s – would be established by his officers.

He told the programme that it would be “silly to speculate whether there was a cover–up”. He added: “As an investigator you have to go with an open mind, if people make that allegation I will take it seriously. But I can assure you there will be no cover-up while I’m here.”

He said the 40 detectives looking into the fresh claims were often confronted by a huge mountain of paperwork involving thousands of boxes as well as the “real challenge” of filling in the gaps when files were missing.

“There are a series of claims over quite a long period of time and not all of them are linked, although in the public imagination they may be in that it is child abuse,” he said.

“You have got the extra complication of people in power and was there a cover-up? I’m determined we will get to the bottom of this so we are talking to the witnesses and all the people who have got information.”