London: British Prime Minister David Cameron vowed on Monday to leave “no stone unturned” in investigating allegations of child abuse by politicians in the 1970s and 1980s, amid accusations of an establishment cover-up.

He was speaking ahead of the expected announcement by his government of a wide-ranging inquiry into the alleged abuse and whether the authorities ignored it.

“I am absolutely determined that we are going to get to the bottom of these allegations and we’re going to leave no stone unturned to find out the truth about what happened — that is vital,” the prime minister said.

Long-running rumours of an organised ring of paedophiles in Westminster have resurfaced following revelations of historic child abuse by celebrities such as the late BBC presenter Jimmy Savile.

The rumours focus on a dossier compiled by late lawmaker Geoffrey Dickens in 1983, which is thought to have contained allegations of child sex abuse against a number of members of parliament and other public figures.

It was passed to the Home Office, or interior ministry, but subsequently went missing.

Following a review last year, the ministry has now revealed that in total, 114 files relating to child abuse allegations it received between 1979 and 1999 were “presumed destroyed, missing or not found”.

It has also identified 13 “items of information” about alleged child abuse, four of which had not been reported to the police, although detectives have now been informed.

Norman Tebbit, who held a series of senior posts in Conservative prime minister Margaret Thatcher’s government in the 1980s, said on Sunday that there “may well” have been a cover-up.

“At that time I think most people would have thought that the establishment, the system, was to be protected and if a few things had gone wrong here and there that it was more important to protect the system than to delve too far into it,” he told the BBC.

By Monday lunchtime, more than 72,000 people had signed a public petition demanding an independent national inquiry, after the issue hit the front pages.

Meanwhile the minister who led the Home Office at the time the Dickens dossier went missing, Lord Leon Brittan, issued a statement on Monday insisting he had behaved appropriately.

He confirmed he had received a “bundle of papers containing allegations of serious sexual impropriety” and said he passed them onto the relevant ministry officials “as was the normal and correct practice”.

Brittan on Monday confirmed he had himself been interviewed by police over a “serious allegation” that media reports concerned a claim of rape, which he denied.

Theresa May is to set out the details of an “independent and authoritative” inquiry into how the Home Office handled allegations of child abuse against politicians in the 1980s, amid mounting calls for a full public inquiry to run parallel with a criminal investigation.

The home secretary is under pressure to explain how her department lost or destroyed more than 100 files related to alleged organised paedophilia, as the government confirmed that four previously undisclosed allegations were handed to the police only last year.

The chancellor, George Osborne, said on Monday that the government would find an “independent and authoritative way” to get to the truth about any child abuse at Westminster.

Speaking from India, where is currently touring with the foreign secretary, William Hague, Osborne said: “We need to get to the truth we need to get to the bottom of what happened in many of our institutions, including potentially at Westminster.”

A Home Office spokesman said an internal investigation by an independent expert last year found “13 items of information about alleged child abuse”.

He said: “The police already knew about nine of those items, and the remaining four were passed to the police immediately. It is important that we do not pre-empt or prejudice any related police investigations.”

The shadow home secretary, Yvette Cooper, has insisted there should be an independent review into how the Home Office handled the allegations at the same time as there being a criminal investigation into the claims.

“The priority has got to be the criminal investigations. At the same time you can have a full investigation into what happened within the Home Office,” Cooper told BBC Radio 4’s Today programme.

She said the internal review of how the Home Office handled the allegations had been inadequate.

Her comments come after Lord Tebbit said he believed there may have been a political cover-up of the child abuse allegations against politicians in the 1980s.