David Cameron has ordered a fresh investigation into what happened to a missing dossier of alleged paedophile activity involving high profile politicians in the 1980s.
The missing file, containing the explosive allegations, was handed to the then home secretary Leon Brittan, by the Conservative MP Geoffrey Dickens.
Lord Brittan admitted handling the dossier and turning it over to officials, but no subsequent action was taken. He insisted he dealt properly with the dossier handed to him in the 1980s.
The Prime Minister has now ordered the most senior official at the Home Office to conduct the internal inquiry, following pressure from former ministers and campaigners.
Cameron said he understands the concerns surrounding the dossier.
"That's why I've asked the permanent secretary at the Home Office (Mark Sedwill) to do everything he can to find answers to all of these questions and to make sure we can reassure people about these events," he said.
"So it's right that these investigations are made. We mustn't do anything, of course, that could prejudice or prevent proper action by the police. If anyone has information about criminal wrong-doing they should, of course, give it to the police."
The Daily Telegraph reported that the dossier included the name of a former Tory MP who was found in possession of child pornography videos.
The politician was allegedly stopped by Customs while driving back to the UK via Dover, and was found to have explicit videos of children "clearly under 12".
The newspaper reported that the politician was not arrested or charged following the incident in the 1980s, and the videos and paperwork have subsequently gone missing.
The Customs officer is said to have spoken to detectives on Operation Fernbridge, an investigation into allegations of sexual abuse by people including high-profile figures.
The report focused on the Elm Guest House in Barnes, southwest London, where there were allegations that senior members of the establishment abused children.
Former Lib Dem MP, Cyril Smith, about whom allegations of serial child abuse have emerged since his death in 2010, was believed to have gone to the Guest House.
Labour MP Tom Watson, who has lead calls for a comprehensive inquiry into historic child abuse, said he was writing to DPP Alison Saunders to ask her to examine the evidence relating to the unnamed Tory politician.
"It's a remarkable revelation," he said. "If true, it shows that a crime was not investigated but also is shocking because it's yet another example of intelligence going missing. I hope the DPP will share the concern of many MPs about this.
"It has got to be fully investigated and also shows why there are a growing number of calls from people for a wider overarching inquiry into historic allegations of abuse."
Simon Danczuk, the Labour MP who exposed the late Liberal MP Cyril Smith as a paedophile, criticised the PM's decision to conduct an internal inquiry, claiming it was not sufficient to win back the public's confidence.
"[Cameron's] statement today represents little more than a damage limitation exercise. It doesn't go far enough. The public has lost confidence in these kind of official reviews, which usually result in a whitewash. The only way to get to the bottom of this is a thorough public inquiry
The Metropolitan Police said: "We are not prepared to give a running commentary on Operation Fernbridge, which is an ongoing operation."
Meanwhile, it emerged that four more cases of historic sex abuse have been referred to the police by Home Office officials in recent months, following a review ordered last year covering the period 1979 and 1999.
A review of a database containing details of more than 746,000 files identified 13 items of information about alleged child abuse, including four cases involving Home Office staff.
Nine of these items of information, including all of the cases involving Home Office officials, were either already known to the police or were reported to them by the Home Office at the time.
The remaining four have now been passed to the police for a "proper assessment", although the investigator who carried out the review said the information was likely to be of "limited value".
Meanwhile, Home Affairs Select Committee chairman Keith Vaz has asked the department and the Home Office for further information. He said: "It would be inappropriate to comment further until we have responded to the chair's request."