Media playback is unsupported on your device Media caption David Cameron says the Home Office must "find answers"

David Cameron has asked a senior civil servant to "find answers" about a missing dossier on alleged paedophiles at Westminster in the 1980s.

The Home Office has faced calls to explain why the dossier was "not retained" by officials.

The document was passed by Tory MP Geoffrey Dickens to then Home Secretary Leon Brittan, who says he in turn handed it to officials.

Labour leader Ed Miliband says a "serious review" is needed.

While No 10 has rejected calls for a public inquiry into child sex abuse claims, Mr Cameron said it was "right" to make investigations.

Senior civil servant Mark Sedwill has been tasked with making inquiries into what happened to the dossier.

'Find answers'

We need to understand what happened to that information Ed Miliband, Labour leader

BBC political correspondent Vicki Young said Downing Street has rejected calls to set up an inquiry into the allegations along the lines of the investigation set up by the government in 2010 into the Hillsborough stadium disaster nearly 20 years earlier.

Mr Cameron said he understood people's concerns about the missing dossier and added: "That's why I've asked the permanent secretary at the Home Office to do everything he can to find answers to all of these questions and to make sure we can reassure people about these events.

Image caption Leon Brittan was home secretary between 1983 and 1985

"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 any information about criminal wrong-doing they should, of course, give it to the police."

Mr Miliband said: "The very least that needs to happen is the Home Office needs to have a serious review of what happened there, because obviously there was information passed to them.

"We need to understand what happened to that information. All of these kind of allegations must be taken very seriously."

'Powerful' dossier

Mr Dickens, who died in 1995, had believed the dossier would "blow the lid off" the lives of powerful and famous child abusers, his son has said.

The long-standing campaigner against child abuse passed the dossier to Lord Brittan, who has said he passed it on to his officials and raised concerns about some of the allegations with the director of public prosecutions.

Mr Dickens's son Barry has told the BBC his father would have been hugely angered that the allegations had not been properly investigated.

The Home Office held an independent review last year into how it handled the documents, after concerns were raised in Parliament.

A letter from Lord Brittan to Mr Dickens was found during the review, saying that the allegations had been acted on.

The review concluded that the "credible" elements of the dossier which had "realistic potential" for further investigation were passed to prosecutors and the police while other elements were either "not retained or destroyed".

Image caption Conservative MP Geoffrey Dickens, who died in 1995

The conclusions were published last summer, but shadow home secretary Yvette Cooper has now said the entire report should be made public.

She also wants Mr Cameron to set up an overarching review, led by child protection experts, to draw together the results from several different investigations and institutional inquiries.

"The prime minister is right to intervene to demand a proper investigation into the allegations of child abuse not being acted upon by the Home Office, because we have not had answers from the home secretary," she said.

"We also need assurance that the police have been given full information now and are investigating any abuse allegations or crimes that may have been committed."

The Metropolitan Police's Operation Fernbridge is investigating allegations of child sexual abuse in the late 1970s and 1980s at the former Elm Guest House in Barnes, south-west London, the scene of alleged parties involving MPs and other members of the establishment.

Greater Manchester Police are investigating allegations of abuse by ex-MP Sir Cyril Smith at Knowl View, a Rochdale children's home which closed in 1994. Officers are also looking at claims the authorities covered this up.

But calls are growing for an over-arching national inquiry, with hearings held in public.

More than 120 MPs have signed a letter to the home secretary calling for such an inquiry.